THE VOLUMETEXC T i m T X O H S OF SIMPLE GXXG3HATED OBGANIC MOLECULES
WITH GESOTK (I?) IN GLACIAL ACETIC #CID
%
Orville H # Hinsvark
A THESIS
Submitted to the School of Graduate Studies of Michigan
State College of Agriculture and Applied Science
in partial fulfillment of the requirements
for the degree of
DOCTQH OF PHILOSOPHY
Department of Chemistry
19SL
ProQuest Number: 10008223
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AGKNOkXEBGIOTT
The author wishes to express bis sincere
appreciation to Dr. K. G* Stone for his expert-*
eneed counsel and guidance throughout the oourse
of this Investigation*
Grateful acknowledgment is mad© to the
National Science Foundation (NSF-G281) for the
financial assistance given throughout the work*
Acknowledgment is also made to Dr. G. F.
Smith for providing the iron (XX) perchlorate
and to my wife for her assistance in the
preparation of the manuscript*
11
v m
nam t
Orville N. Binsverk
Born*
June 16f 1921* in Sioux Falla, South Dakota
Academic Career*
Sioux Falls high School
Sioux Falla, South Dakota, (1938-191*2)
South Dakota School of Mines
fiapid City, South Dakota, (191*6-1950)
Michigan State College
Emt lancing, Michigan, (1950-1951*)
Degrees Held*
B. Bm South Dakota School of Mines (1950)
M, 3, Michigan State College (1952)
Thesis titles A Mechanism for Decomposition
of Potassium Ferrate (VI) in Aqueous Sodium
%droxide
$hilc investigating the fedibility of applying seetle acid sole*
tioas of cerium (Vf) to oxidimatric detera&nationa, the following
observations eere noted,
(1) Because of the higher concentration of oxidant obtainable
through ite use,
u
m
Li b hexsnitrstoeerate (It) ie employed in the
preparation of acetic sold solutions of cerium (ft),
(2) &n asperoiaetrie method esaploylng % m active electrodes provides
an e m e U e i d means for obtaining the end points of the titrations,
(3) Cerium (It) in acetic aoid Is reasonably stable in the absence
of light or mineral soldo,
(h) Sodium oxalate is m excellent reagent for us© in the standard*
iaation of the cerium (I?) solution*. loanee of the interference of
nitrate, iron (XI) perchlorate cannot he used for analysing cerium (X?)
solutions prepared from m m t & m hexanitratocerate (IV) j hut this re*
agent provides a moans fen* obtaining good results in the standard!*
cation of acetic sold solutions of sodium permanganate or chromium
trioside.
(5) Sodium oxalate and sodium mesomalats are determinable in the
presence of a olds variety of oxygenated molecules. Since m empirical
method malt he used in detecting the end point, the results ere less
satisfactory for the titration of malonlo add or citric acid} but
reproducible results can he obtained.
lv
(6) Carbon dioxide %»
oniy volatile product detected In tlm
o x ! 4 « 6 k w t An < w t e t atoichiometric reaction between the eolvent
«ad reduotant 1*
by the uee of l-carbon~lk eoetic aeid in
tbe oelveat, the retlno of total sole* of osita dioadde to mole* of
carbon diontd* derived from tbo advent wo*
s*dn» oxalate* 2«1|
eodiuai aeeoxelat©, lilj ©©Ionic acid, 2 i2j m d citric ©eld, 3*3*
(t) $t» vopldlmi of tbe redox potential of tbe ©eriun ayete®
under vsrioua condition* of acidity v^geit* 001uplox fematton in tbo
©eetic acid,
flioso ftoeos^pliohaexrts * * m to Illustrate partial fulfillment of
the broad objective* ©aifibliahed at tbe beginning of th® investigation*
v
table m Q c m m s
Page
XNTRGBUOT01I............ ........... .......... ..... .... .....
1
HISTQRX
3
*.....
SIPERM33TAL
8
A*
B. Apparatus,,...........
C. Preparation of Solutions...............................
1. Ammonium Hexenitratoceret© (
X
V
J
2. Sodium Fermanganate
..... *.....
3. Chromium T r i o x i d e . . ...........
L. Iron (XX) Perchlorate.
....
5. Load Tetra~acetat©
............. .........
0. Solubility of Cerium (X?) Salta in Glacial Aeetie Acid....
B. Detection of Equivalence P o i n t * ...........
....
1* PotenticraetriQ Titration.
2. Amperometrlo Technique with Two Active Electrodes....
F. Standardizatlon of Oxidants
..........
1. Arsanious Oxide.
.....
.......
2. Stannous Chloride
3. Sodium J&trite.....................
L. Hydroquincme
....
..........
5. Iron (XX) aalta*.
a. Standardlzation of Aeetie Aeid Solutions of
Chromium Trioxide or Sodium Permanganate by
Iron (XX) Ferohlorate.............
b, Detection of Iron (II) %$tem End Point...,....,
e . Determinations With Aeetie Acid Solutions of
Iron (XX),..
......
6. Sodium Oxalate.........
0, Stability of Aeetie Aeid Solutions of Ammonium Bexanltratoeerate (XV),..,..,....
1. Fbotosensitivity of Cerium (XV) Solutions..........
2. Stability of Aeetie Aeid Solutions of Cerium in the
Presence of Perchloric A d d ,
.......
3 . Rqploymeat of Back Titration Technique..
3
6
H. Comparison of the Cerium System Redox Potentials in Acetic
A d d Solutions of Perchloric Aeid tsid Sulfuric A c i d U
X, Determination of Carbon Dioxide Evolution.
........
J. Radioactivity Measurements on Evolved Carbon Dioxide......
vi
8
9
9
9
10
10
11
11
IP
15
15
16
1?
18
18
18
18
19
21
23
25
29
35
35
37
o
L6
h9
TABLE OF CONTENTS . Continued
Page
K, Indication of Peroxide Formation During Cerium (X?)
............
Oxidation...
...................
5k
OXXDATXOHS........... ......
A,
B,
C,
D.
E.
F.
%droquinon©....,.......
Sodium Oxalate,.........................................
Sodium M e a o x a l a t e
.....
Malonie A
e
i
d
,
W
Citric Acid..........
....
Miscellaneous Oxidation*.......
1. Derivative* of HaXonle Aeid,..,.,..,......
2. MetJcrlen* Diaceiate, Methyl Formate, Methyl Acetate,
and Ethyl Acetate.
......
3. Oxalacetle Acid and Pyruvic Aeid....,
...........
h, Tartaric Acid,,
.............
5. Saeeinie Aeid.
..............
6 . Aeotylfleetone..,
..................
7« Formaldehyde and Bene aldehyde
*
8, Glycolic Acid and Lactic Aeid,,.,.......... ..........
9. Ithyl Alcohol end Methyl Alcohol..............
10, Sucre**, <&yearol, mod Ethyl@m Glycol..
8
9
11, Cinnamic Acid, Kaleic A d d m i Cyclobsxene....... .....
12, 2,*Mfcliaethyl~3~H33yne~2,5-Biol... *....
13* 2-Mer©aptobea*thiacol
.....
Discussion cr r n r n m m ..........
A, Oxidation of Sodium Oxalate.......
B, Sodium Meaoxalaie*.
.....
C, Citric Acid and Malonlo Aeid.
....
OTOIARX.,.
52
......
5h
5?
61
76
81*
81*
8$
86
87
87
87
88
88
88
89
92
93
9k
95
97
98
100
L3TS3UTURB CITBD...............
103
JFFSWXOB&ft,
105
vii
tm m t/m
TABLE
Page
1 Saturated C© (17) Concentrations in Aeetie Acid.,*.,*****.**.
XX Stability of Iron (IX) Perchlorate Solution**,,,*.......
1X1 Sensitivity of A$*g>er©*a©irte End Point Fe(C10*)a Titrated
dthBfifc^4 .*******,*****..... ...... *.... ********.......
17 Cob$>arisen Between B&aCa04 and F©(C104)a Determination of
0«Mn04 **,*********....
V Comparison Between KX and F©(S104)a Determination of CrOa,*,,
VI Comparison of ۩{XV) Beterminationst
NaaCa04 vs* FeS04 ******
12$
23
25
27
28
30
VXX Beteiwdnation of B a ^ a04 with Known Purity (B^) aCe(NOa)€,*** 31
tm
Sensitivity of Anperonetrlc End Point ®arf!a04 Titrated With
Co (XV)****....... ***..**♦*.*•*.............
32
XX Reproducibility of Determinations of Acetic Acid Solutions
of Co (XV) with Ma^gOg*...******_,...****.*..*.**....*****
33
X Light Sensitivity of Acetic Acid Solution of Ce (XV),********
36
XX Stability of Acetic Acid Solutions of Ce (XV) Containing
BC104 ,**.......
*****..... ****..**.♦.
38
XXX Excess Technique for Determination of H a g C ^ .......*.....
XXIX Effect of Acid on th® Potential of the Ce XXX 0© XV Couple
in Aeetie A d d Media*****
*****......
39
1*3
XXV C0a Formation in th© Oxidation of Various B e d u c t a n t s h @
XV Degree of Solvent Participation Doing CHaC**OaH,,,*,**,....
51
XVX %drocdnone Titration with Ce (XV),**,..... *,***,*.*.•.***
55
XVXX Effect of Oxygenated X^urltiee on th© Oxtdimetric Titration
of Ma^Ca04 .................. *****......
will
59
l»m m
TABLES - Continued
XVXIX Stoichiometry of Sodium KesoxsXate Oxidations
......... 6j
XtX Bffeot of Oxygenated Impurities on the Oxidixaetric Titration
of Sodium Hesoxalate, *,,***,.....
65
XX Melonie Acid Determinations with Ce (IV) in Glacial Aeetie
Aeid,**,........ .....
TO
X U Fb(OAe)4 Oa&dation of Ce (IV) Oxidation Product of Halonic
....
Acid,*,
75
M X
Excess Technique for the Determination of Malonic Acid*,.*,.
77
M I X Citric Acid Determination by Acetic Acid Solution of Ce (XV)
80
XXXV Lead Tetra-acebai© Oxidation of Ce (XV) Oxidation Product of
Citric Acid..,**,**.*,....... *....
82
ix
him m F tamm
nm m
Page
1. Fotentiometric Curve Demonstrating Coincidence of
Equivalence Point and Diphonyl amine ColorCh©nge............
20
2, Typicel Aaperometric Titration Curvet 1*9,6 mg. Na^J304
tilth 0.0287 ti Co (IV) Solution.,.... ...................
3l*
3* Potentlowetrio Titration Curve tinder Various Conditions of
Acidity................
Ut
I*. Schematic Dreeing of Apparatus for Determining Evolved
Carbon Bioadde,...... ................. ..... .
1*7
5* Aa^erometric Titration Curve of %droquinone.. 56
6, Absorption Spectra of Cinnamic Acid end Its Cerium (XV)
Oxidation Product
.... .............
x
91
XKTBODUGTXOW
1
INTRODUCTION
Recently non-a*ru®oua solvents have been receiving ® great deal
of attention in their application to acid base titrations (21*,25),
acetic acid being the solvent studied most extensively in these
investigations. The acidic character of this solvent makes it
possible to titrate, directly, very weak bases dissolved In this
medium with acetic acid solutions of standardised perchloric acid.
Its physic si and chemical properties coupled with the availj&llity
makes this reagent particularly adaptable to studies of this type.
1^hlle non-aqueoua solvents have been investigated extensively
in their application to acidimstry, titrations Involving the use of
oxidants have been investigated only superficially (33,3k).
A variety of reasons may explain this lack of studys
(l) Insolu
bility of the usual inorganic oxidants in organic solvents,
(2) instability of the reagent in ordinary solvents, and (3) the
excessive cost of the solvent.
Glacial acetic acid because of its relative stability and sol
vent properties has served as a solvent for oxidation studies in
theoreticpX and preparative organic chemical studies (it,13,16,19,
26,31,32).
In many cases utilisation of acetic acid as a solvent
permits the use of an homogeneous solution of reactants and con
tributes to stability and selectivity of the oxidant.
By the
2
utilization of the proper oxidant, advantage may be taken of these
properties to extend the scope of direct organic determinations
using oxidimetry*
Cerium (17) has received a great deal of attention in organic
oxidimetry (17,27,28,29) and since it exhibits a reasonable degree
of selectivity in aqueous media, It seemed to be particularly well
suited for a study of organic oxidations in glacial aeetie aeid*
The ultimate objective of this work was to demonstrate the
application of cerium (IV) in glacial acetic acid to the direct
determination of simple organic molecules*
In addition, data were
to be eolleeted which would aid in the elluoidation of the mechan
ism by which oxidations take place in this medium with cerium (IV)
as the oxidant*
3
BISTORT
Th© concept of oxidation In orgsnic chemistry 1b rather dif
ficult to define,
It Is possible to lucre aee th® apparent
oxidation number of m organic molecule In a variety of ways*
(1) dehydrogenation, (2) direct addition of oxygen to the moleculef
or (3) substitution,
By careful examination of the oxidised mole*
cules, it i® possible to group all of these examples into the
oxidation concept employed In inorganic chemistry, the loss of
electrons. In general organic oxidations proceed with the ultimate
loss of m even number of electrons*
Since all of these definitions exist covering orgsnic oxidations,
one might expect that there would be at least an equal number of
oxidant classes which would cause th© diversified reactions.
In this
work only ionic oxidising agents, a classification used by Waters (13);
were employed. These oxidants m«y be regarded essentially as
electron abstractors as opposed to dehydro gensting agents.
Included
In this class of oxidants ere iron (HI), ferrieyanide, silver (II)
diamine, and eerium (I?)j all of these reagents undergo a single
electron change, It may be noted that these reagents attack only
molecules which contain elements such as nitrogen or oxygen on which
there is at least on® pair of unshared electrons. It has been pro
posed (6) that oxidation of such molecules with ionic oxidants
k
proceeds by th© Initial removal of a single electron resulting In
a free radical. The remaining unpaired electron is very labile
end is abstracted more easily, resulting in an Irreversible process.
Because of the irreversibility of the second step in the oxidation,
it is impossible to obtain an accurate measurement of the potential
necessary to produce an oxidation of the organic molecule.
Several reagents exhibit a reasonable degree of selectivity In
the oxidations they perform. When used in the oxidation of oxygen
ated organic molecules, cerium (XV) in aqueous media Is such m
oxidant.
A set of rules governing the quantitative oxidation of
organic molecules has been presented (28) and reference to them -will
indie ate, to some degree, the selectivity of cerium (IV) in organic
oxidations which are applicable to analytical determinations!
(1) Only those compound®, the electronic configuration of which
is capable of rearrangement to a stable form by the removal of two
electrons and two protons, are oxidised.
(j) Th® carbonyl group must hydrate to a glycol form before it
can be oxidised.
(h) Compounds containing m active methylene group are oxidised.
(5) Cowgjoumds yielding aldehydes or ketones, unsubstituted by
oxygen in the alpha position, as end products are not quantitatively
oxidised and give empiricsi results.
(6) Ibd products are fatty acids, ketones, aldehydes (other
than formaldehyde), and carbon dioxide.
5
(?) Formaldehyde 1* rapidly hydrated sand the hydrate la rapidly
oxidised to ferrate acid. This Is a specific property of cerate
oxidations as distinct front periodate oxidations*
These rules hold only for aqueous media end it might he expected
that different results would be obtained when the oxidations ere done
in another solvent * One would expect that the solvate formed in a
non-aqueous solvent would differ in reactivity from that of the
corresponding hydrate.
Glacial noetic acid has been employed extensively as a solvent
in preparative and theoretics! organic oxidations (li,13>16,19,26,31,
32), especially for those oxidations involving the per acids, lead
tetr©-acetate, and chromic acid*
Its utilization as a solvent in
direct volumetric oxidation has been limited to a series of papers
by Tomecek end co-workers (33,3b). These investigations concerned
themselves with the study of various ©xLdants which were soluble in
glacial acetic acid by using them in the titration of inorganic
reduotsnts and a few organic substances *
The progress of the reaction and detection of equivalence point
were determined potentiometrlc ally« The cell used in the potentiometric measurements was a saturated calomel electrode as the refer
ence electrode and platinum as the indicator electrode.
Bromine was the reagent receiving the most attention.
Chromic
acid, sodium permanganate, lend tetra-acetate, iodine, iodine monochloride , iodine monobromide, and hydrogen peroxide received less
attention * %drogen peroxide, iodine, and iodine monobromide showed
6
no promise * Since iodine monochloride underwent the ease reactions
so bromine, although less effectively, It received little study.
Bromine in acetic acid was the system which received the most con
sideration. By adding sodium acetate to the solution being titrated,
it was possible to titrate some molecules directly to a potentiometrlc end point, Among the substances which were found to be
determinable in this way weret
N-disaethylaniline, aniline, bexusyl-
meraaptan, bydroqulnon©, and ascorbic acid.
One immediate and
obvious difficulty involved in the ©Employment of bromine is that in
addition to oxidation, substitution and addition reactions must be
considered.
If possibilities exist for more than one of the re
actions to occur, the results may well be erratic«
By careful purification of the solvent, stable solutions of
sodium permanganate and chromic acid were reportedly obtained,
Among the oxidants studied, only those two ionic reagents were
investigated, the titrations conducted with these were principally
of inorganic reduet ants; however, a few organic oxidations were re
ported,
Diphenylamine, p-aminophenol, and hydroquinone were found
to be directly titrstable with acetic acid solutions of chromic acid
while sodium permanganate was used only in the titration of bydroquinone.
Solutions of lead tetrs-acetat© were found to be quite
stable; and although the equilibration of the potential was slow
throughout the titration, they reported that measurements of ascorbic
aeid, mandello sold, and benzyl mereaptan were satisfactory by a
direct titration with this reagent.
7
A H of the titrations were conducted on a serai-micro scale
with a volume of about two ml. being used in most titrations. The
data given by the authors concerning their work were too limited to
evaluate the applicability of the systems to quantitative organic
analysis.
JOTBRIHMTAL
8
EXPERIMENTAL
A,
Reagents
Merck “Be&gent Grade** and B@ker,s “Analyzed" Aeetie Acid ware
both used aa solvents,
In the titrations with G©(IV) further puri
fication of the aeetie aeid was found to be unnecessary; however,
in the studies concerning stability, precautions were taken to
eliminate oxidizable impurities.
Purification was accomplished by
one distillation from chromium trioxide followed by a second dis
tillation from potassium permanganate.
The iron (II) perchlorate, 70$ perchloric ©old, end cerium (IV)
salts were obtained from the 0, Frederick Smith Chemical Company.
Merck “Reagent*1 primary standard purity sodium oxalate, Baker*a
“Analysed0 chromium trioxide, and Fisher Scientific Company “CP Grade*1
sodium permanganate were used, Merck “Reagent Grade** citric acid
was employed,
Row Chemical Company m&lonle acid was further purified
by reeryst alliz ations from water followed by reeryst&Llisation from
ether. The final product was found to be 99,1% pure by titration
with standard sodium hydroxide,
Eastman Kodak Company “White Label0
acetic anhydride was used. The other reagents were prepared by
accepted procedures.
The studies involving carbon-ll* acetic acid were carried out
with 0,1 millicurie (©a, 8 mg,) sodium acetate with the carboxyl
9
group legged obtained from Ghem Had Division, Nuclear Instrument
and Chemical Company,
B * Apparatus
A Fisher Eleedropode (sons, * 0,025 micro m p per scale
division) ©quipped with 2 cm, 18 gauge platinum wire electrodes and
a Sargent Potentiometer ( It volt span) wore used for the detection
of equivalence points,
/ magnetic stirrer was used and provisions
were made for Introducing a stream of nitrogen into the solution
being titrated. In the radio-isotope studies a Nuclear Scaling
Unit Model 163 in conjunction with a Trseerlab Vindowleaa Flow
Counter, S C 16, fed with Matheson Geiger Flow Qas (Helium-isobutane)
was used for the counting.
The light sensitivity of the solution of Ce (IV) required the
use of amber burets for the titrations,
A Fisher Orsat Type gas
analyser was used in the attempt to detect combustible gases evolved
from the oxidation,
C,
Preparation of Solutions
1, Ammonium hexanttr&tocerete (IV)
Ammonium hexanitrstocerate (IV) hexahydrete was dried at 105°C,
powdered, and added in large excess to glacial aeetie aeid, The
occasionally stirred suspension was heated to 60°C and held at this
temperature for a minimum of four hours. The mixture was allowed
to cool slowly by standing in the dark overnight, and was filtered
10
through a sintered glass filter of M porosity,
The solution v m
standardised by titrating sodium oxalate dissolved in glacial acetic
acid made 1 K with respect to perchloric aeid.
The end point mas
detected axaperoroetrically with two active electrodes,
2. Sodium Permanganate
Sodium permanganate was used in preference to the corresponding
potassium salt because of Its much greater solubility in aeetie acid.
The permanganate solutions were prepared by dissolving the spproxl*
mate weight of sodium permanganate in enough purified acetic acid
to make the desired concentration. The actual concentration of the
permanganate solution prepared in this way was found by titrating
a weighed amount of primary standard sodium oxalate. The sodium
oxalate was dissolved and titrated in m aqueous medium made acid to
the extent of 2 ml, sulfuric acid per 2$ ml. water.
The end point
was taken at the point where the permanganate color persisted for US
seconds. The fading of the color at the end point made th© detection
of the equivalence point rather indefinitej however, fairly repro
ducible, and apparently reliable, results are obtained under these
circumstances.
3, Chromium Trioxide
These solutions were prepared by dissolving the approximate
weight of chromium trloxide in the desired volume of purified acetic
acid. The chromium trioxide solution was then standardized by adding
11
a measured volume to an excess of 1Q$ aqueous potassium iodide in
a glass stoppered flask* The reaction mixture was left in the dark
for thirty minutes,
At the end of this time, the liberated iodine
use titrated to a starch end point with aqueous standard sodium
thioaulfate (33).
h* Iron (It) Perchlorate
Acetic anhydride in slight excess over that necessary to react
with the water present in the reagent was added to the measured
amount of glacial acetic aeid. After flushing the acetic sold with
nitrogen, the approximate weight of iron (IX) perchlorate yto make
the desired concentration,was added. This solution was left under
a nitrogen atmosphere for a minimum of two hours, but frequently for
much longer* To determine the actual concentration, a measured
volume of the iron (XX) solution was added to a solution of 5 ml. B$%
phosphoric acid in 20 sd* water. The resultant solution was titrated
to a diphenylamine end point with s standard dichromate solution
prepared from primary standard potassium dichromate,
5, lead Tetra^aoetate
The reagent was prepared by adding dry red lead slowly with
efficient stirring to a solution of acetic acid and acetic anhydride
which was held at B0°C (11)* The lead tetraacetate separates as
a solid on cooling the solution. After recryst sllizing the solid
from acetic acid and drying under vacuum over sodium hydroxide, an
12
approximate weight was added to enough acetic acid to give the de
sired concentration. The eolation was standardized iodometrically
in the acme meaner as the chromium trioxlde solutions (33)•
The solution prepared according to there procedure® were used
In various places throughout the work.
B. Solubility of Cerium (I?) Salts in Glacial Acetic Acid
The limited solubility of most cerium (1?) salts in acetic acid
required m investigation to ascertain which salt of this oa&dsnt
could be employed to the greatest advantage in this medium. Before
determinations Involving the oxidising ability of this reagent
could be studied, reasonable solubility must be attained.
The Salts used were commercially available eerie sulfate, ammonium
tetrasulfato cerate (IV), and ammonium hexanitratocersi© (XT) obtained
from the 0. F. Smith Chemical GompabF*
Cerium (IT) hydroadd® was
prepared by the precipitation of cerium (XT) from an aqueous solution
of ammonium hexanltratocerste (XT) with aqueous ammonia. The precipi
tate was collected by filtrationj and after washing with water, it
was dried by washing with acetone and leaving it exposed to air.
For saturating the acetic acid with the cerium (IT) salt, the
salt was powdered and added In excess to acetic acid. The suspension
was heated to approximately 60°C and shaken occasionally. This heat
ing was maintained for a minimum of four hours.
After this time, the
suspension was placed in the dark and allowed to oool for at least
twelve hours, and then filtered through a sintered glass funnel of
13
medium porosity, A cerium (I?) determination was made by using a
suitable reduotant according to procedures given in later sections.
^ t h the exception of the nitr^tocerste solutions ell cerium (1?)
determinations sere made with standardized acetic acid solution of
iron (IX) perchlorate serving as the reducing agent.
In the absence
of the nitrate, iron (XX) solutions are more convenient to use since
the sfpproach to the end point is more apparent. This factor is of
particular importance in the determination of cerium (X?) when
present in very small concentration.
In the titration, a measured
volume of the standard iron (IX) solution eras added to the titration
vessel under a nitrogen atmosphere,
Two ml. of TOSS perchloric sold
mere added, end the titration conducted to an smperoraetric end point.
Xn this titration the current flow passes through a maximum, proceeds
to aero and then increases sharply with the first excess of cerium (XV).
Since nitrates interfere with determinations involving iron (XX)
perchlorate in acetic sold, the concentrations of cerium (I?) solution
were determined by the oxalate procedure when ssnmonium hexsmitratocerate (IV) was used, A complete description of this procedure is
given in the section entitled BStandardization11.
Table X lists the approximate cerium (XV) concentration when an
excess of the particular cerium (XV) salt is placed in contact with
the acetic acid using tha prescribed procedure.
These data show that the most favorable solubility Is obtained
through the use of ammonium hexanitr§t,ocerate (XV). The higher
Hi
TABLE X
Q k T m a m C© (XV) COHCiatTKOTOfiS m ACETIC ACID
Cerium (XT) Salt
Ce(S04)a
Approximate Normality
< O.OQ5
Om.)a Ce(S04),
0.005
Ce{OH)4
0.01
(HH4)a Ce(S03)a
> O.Oti
solubility obtained with this reagent indicates a elder range of
applicability*
For that reason, ammonium hexanitratec©rate (IV) was
used elrnoat exclusively in preparation of the oxidizing solutions
which were used in studying possible analytical applications to
which acetic acid solutions of cordon (X?) could bo applied.
When a mineral acid such as sulfuric, nitric, or perchloric acid
was used to wot the cerium hydroxide and the resultant product was
put in acetic acid, the color intensity of the solution indicated
much greater cerium (XV) solubility* this increase in solubility
was offset by the much greater rate of decomposition of the resulting
solution. Complete loss of color and simultaneous loss of oxidizing
power occurred in a few hours*
The information collected in these investigations indicated that
the most promising salt to study was ammonium tosxanitrotocerate (XV).
15
E* Detection of Equivalence Point
the high color developed In some of the oxidations end the
insolubility of the usual cerium (IV) indicators in acetic acid
solution* of perchloric sold mad© m electron©trie technique
necessary for following the progress of the titration.
1* Potantiometrie Titration
The use of a cell consisting of a saturated calomel reference
electrode and a platinum electrode was satisfactory for detecting
the end point| however, the magnitude of the observed potentials
varied*
The unreliability of the observed potential can be attrib
uted to the instability of the saturated calomel reference electrode,
Instability of the electrode might be expected since a large and
uncertain liquid junction potential would be developed at the inter
face of the two solutions, acetic acid and aqueous potassium
chloride. Tbs magnitude of this liquid-limiid junction potential
would very m diffusion takes place and the solvent characteristics
change*
In addition to the liquid junction potential, diffusion of
the acetic acid into the cslomel cell would probably cause a varia
tion in the activity of the potassium chloride and m a consequence
cause instability of the potential of the reference electrode *
To minimise these effects and Improve the reproducibility of
the observed potential, a silver-silver elloride reference electrode
was used in preference to the calomel electrode* The silver-silver
16
chloride reference electrode was prepared toy making a silver wire
the anode with a platinum cathode and pausing a current through an
hydrochloric acid solution {It).
Using silver-silver chloride and platinum electrodes the
potentials observed during a potentioroetrie titration in glacial
acetic acid were reproducible.
A reproducible change of about 500
mm yas observed at the end point of an iron (II) or sodium oxalate
titration with acetic acid solutions of cerium (If) in the presence
of perchloric acid.
While the change in potential is sharp and of large magnitude,
a certain amount of precaution is necessary to maintain the silver
chloride film when this reference electrode is used.
2. Amperometrio Technique with Two Active Electrodes
In order to circumvent the inherent difficulties of end point
detection by potantiometric means, an attempt was made to utilise
m smperometrio method with two active electrodes (30) for follow
ing the progress of the titration.
This method of end point detection proved to toe adaptable to
most of the systems considered in this work and was the principal
means of detection used throughout the determinations.
A Fisher Klecdropode was used as the source of potential applied
across the two platinum electrodes (18 gauge platinum wire 2 cm.
long). The exact potential applied varied with the system and the
particular potential is given in the individual determinations.
17
In general the potential which wee applied was determined In the
following manner,
A titration of the particular system under eon-
olderation woo carried out*
At the end point the epplied potential
was varied* and with each addition of titrant, the current flow at
a given potential was noted.
The minimum potential at which there
was a maximum change in galvanometer reading for each addition of
reagent was chosen as the value which would be used in ell determin
ations involving the particular reagent,
W m m this method of end point detection was applicable to the
determination, the values obtained for the titrations were reliable
mod reproducible as was demonstrated in subsequent work,
F«
Standardization of Oxidants
The choice of reagent suitable for use in the determination of
the concentration of a particular oxidant dissolved in acetic acid
is made complex by the instability or insolubility in this solvent
of the common redactunts ordinarily employed for this purpose. The
choice of redactant which would be suitable for standardisation of
the oxidant is governed by the following considerations*
(l) The
reduct ant whan dissolved in glacial acetic acid must react rapidly
and in a stoichiometric manner with a glacial acetic acid solution
of tbs oaddexst tinder consideration,
(2) The reductant must be
appreciably soluble in glacial acetic add,
in the acetic add,
(3) It must be stcbls
(k) Its concentration must be determinable by an
independent procedure»
18
Th the process of searching for reduct ©at® suitable for
atandardisatton procedures Several reagents were Investigated!
1. Arasuloug oxide
this primary standard proved to be too insoluble to be applic
able to st andsrdisation procedures. The same difficulty was
encountered in an attempt to use sodium arsenite.
2. Stannous Chloride
This common reduotaut was too insoluble, and cloudiness develop
ing in a saturated solution on atending, indicated instability in
this medium.
3* Sodium nitrite
This reagent is appreciably soluble and a glacial acetic acid
solution of it is oxidised rapidly by Co (I?) solution®.
The salt,
however, is too unstable in this medium to be feasibly employed.
It decomposes with a visible evolution of a colorless gas.
k, iiydroquinoaa
Ifydroqulnone was the principal standard employed by Toraeoek
(33,3k) in his work) and for that reason, deserves some attention.
This easily oxidised material la soluble and stable in acetic acid;
however, uncertainties regarding purity and indications leading to
the conclusion of non-stoicbiometric reactions forced the rejection
of i M s substance for standardisation purposes.
19
5* Iron <») salts
With orai exception, described in the following section, these
salts proved to b© too insoluble in acetic acid to set as reagents
for standardlsation. Investigated in this category were iron (II)
sulfate, ammonium iron (XX) sulfate, 0esperf3 salt (Ferrous etbylenedlamine sulfate tetr ©hydrate), iron (XI) chloride, and iron (IX)
perchlorate.
Only iron (XX) perchlorate exhibited any promise as a
possible reduot&nt in this medium.
Iron (XI) perchlorate conformed .to nearly all of the prescribed
qualifications necessary for the purpose of standardisation of
oxidants in Metis acid.
It possessed good solubility properties
sines 0*1 N solutions of iron (XX) perchlorate In acetic acid are
readily prepared* It reacts stoicl&ometricelly and rapidly with the
oxidants investigated. When stored under a nitrogen abaosphere,
glacial acetic acid solutions of iron (IX) perchlorate are quite
stable! and solutions of iron (XX) perchlorate are easily standardized
by titration with aqueous solutions of primary standard potassium
dlchromate to a diphenylerain© end point, to demonstrate the coinci
dence of the color change with the equivalence point, a potentlometric titration was mad© with the indicator present.
The result
of such a titration is shorn in Fig, 1 *
While solutions of thi© reagent reacted rapidly and quantitatively
with glacial acetic acid solutions of cerium (IF), nitrate was found
to offer a serious interference in this medium. The results obtained
20
800
700
600
COLOR
500
CHANGE
300
200
IOQ
FIG . I
2.0
4.0
ML.
— >
P O T E N T IO M E T R IC
C O IN C ID EN C E
DIPHENYLAM1NE
OF
CURVE
D E M O N S TR A TIN G
EQ UIVA LEN CE
COLOR
5.0
CHANGE.
PO IN T
AND
21
by titration of the iron (IX) solutions with acetic sold eolutions
of ammonium hexsnitratoeerate (XV) veried depending on the length
of tine taken to perform the titration* to substantiate the state*
msxtt regarding nitrate interference, acetic aeld solutions of calcium
nitrate were reduced by iron (IX), ^hen the iron (XX) perchlorate
was added to a solution of calcium nitrate in glacial acetic acid,
made 1 9 with respect to perchloric acid, oxidation took place st
an appreciable rate* This effect was noted by adding the iron (XX)
to the eelcium nitrate solution in which the electrodes, across
which 150 mv. were applied from the Ktoedropode, were dipping. On
addition of the iron (XX) solution, there was an immediate end large
increase in current flow. The galvanometer reading then dropped
off at an appreciable rate to tbs original reading of aero. This
falling off of current is attributable to the depletion of the iron
(II) so that the iron (II), iron (XXX) couple is no longer present.
This rate of oxidation of iron (XX) by nitrate is too slow to afford
a means for a direct nitrate determination! but it does serve to
show the incompatibility of iron (H) and nitrate in this medium.
Since ammonium hexsnitratocer&te (X?) was the cerium (X?)
salt fom d to have the best solubility properties in glacial scetic
acid, iron (XX) perchlorate was discarded as a reagent for the
standardieation of the cerium (XV) solutions,
a.
Standardisation of Acetic Acid Solutions of Chromium Tri
oxide or Sodium Permanganate by Iron (XX) Perchlorate 8 Even though
22
iron (II) perchlorate solutions cannot be employed in the eteadardiz ation of glacial acetic acid solutions of cerium (IV) from ammonium
hexanitratocerate (IV), it does possess certain quantise which
make
it desirable as a redactant to be used in acetic acid.
It
must be recognised that, with the exception of being susceptible
to oxidation by nitrate, this salt conforms to the
requirements prescribed for a reluctant which may be employed in
the standardisation of a particular oxidant dissolved in glacial
acetic acid.
In order to demonstrate the applicability of this
reagent as a reluctant, sodium permanganate and chromium trioxide
were determined by standard solutions of iron (IX) perchlorate.
Sodium permanganate Is quite soluble in acetic acid end seems
to offer some possibilities as m oxidant for organic molecules.
Chromium trioxide in this medium has been used for some time as an
oxidant in structural determinations and theoretical considerations
in organic chemistry (h,13,16,19,26,31,32) ♦ Iron (II) perchlorate
In acetic acid provides a solution suitable for the determination
of either oxidant without introducing aqueous reagents into the
oxidation reaction.
Acetic acid solutions of iron (II) perchlorate, sodium per*
msnganate, said chromium trioxide were prepared and standardised by
the methods described in a previous section.
If no precautions are taken, Iron (II) perchlorate solutions
are slowly oxidised by air.
Evidence for this instability toward
33
sir oaddetios of acetic sold solution of iron (XI) perchlorate is
presented In Table XI. Tit© data found in thin table wore collected
by titrating measured volumes of the iron (XX) solution with
aqueous standard potassium dlohroraat® at the listed tines.
TABLE XI
m m tm t or mm (11) fmcm/cam® soimims
Days
K Under Air
H Under »„
0
0,0265
0.0265
X
0.0256
0.026U
3
0 .02U0
0.0265
The values show that when the acetic sold Is flushed with
nitrogen prior to dissolving of the Iron (XX) perchlorates and If
the solution Is stored under nitrogen, no appreciable decomposition
takes place in three days. These values are compared to the values
obtained when no precautions are taken to exclude air from the solu
tion, here appreciable oxidation has occurred. By passing a stream
of nitrogen through the solution being titrated, air oxidation of
iron (XI) is minimised and sharp and reproducible end points are
obtained by the swperometric technique»
b.
Detection of Iron (XX) System End Pointi During the titration
of iron (XX) perchlorate, the solutions become too highly colored to
2h
permit the use of redox indicators, the color presumably being due
to the iron (XU) formed in the particular oxidation* Non-reproduc
ibility of potential measurements ©ploying a calomel reference
electrode, and the difficulties encountered in employing a silversilver chloride electrode mad# the use of a potentlometric method
impractical for detection of m ©
a: ^
lu
CL w
i—o
CD
CM
CM
u.
35
These results show the reproducibility thst is possible when
tedium oxalate is employed in the standardisation of ammonium
hexanitrelocerete (IV) dissolved in glacial acetic acid*
This reagent conforms to all of the requirements adapted as
being necessary in the si endardieation of this oxidant*
sttble.
(2) Simply through weighing, known concentrations of
redaotant ere obtained,
solvent,
dant,
(1) It is
(It)
(3) It has appreciable solubility in the
It resets rapidly and stoichiometric ally with the oxi
Since it does conform completely, sodium oxalate was adopted
as the reagent to be used In standerdilation of all cerium (IV)
solutions,
G, Stability of Acetic Acid Solutions of Ammonium
Bsxanitratocorat© (IV)
On the bases of the slow oxidation of acetic acid by cerium (IV)
in aqueous media (12,19,26) one might expeet that acetic acid solu
tions of cerium (XV) would be somewhat less stable than the corres
ponding aqueous solution.
Before this system could be investigated
for analytical applications, it was necessary to determine cerium
(IV) stability in an acetic acid medium.
1 , Photosensitivity of Cerium (IV) Solutions
By analogy to the light sensitivity of some cerium (IV) salts
In aqueous media (26) , it would be expected that light would have
some effect on the stability of cerium (IV) in acetic acid.
36
Te deaxmstrate the relative *rtability of acetic ®cid solutions
of eramcnlum hexanitratocerate
(XV) stored in light and dark, a
solution, prepared by the method previously described, was divided
into two portions. The acetic acid hoi been carefully purified by
distillation from chromium trioxide followed by a distillation away
trm potassium permanganate. The two portions of the cerium (IV)
solution were placed in glass stoppered flasks, one of which was
eleir and the other completely protected from light. The two flasks
were stored side by side on the desk top and exposed to the normal
laboratory radiation. At the time intervals listed, the respective
cerium (XV) solution was used to titrate a weighed sample of sodium
oxalate in the manner previously described. The concentrations of
tha two solutions are given in Table X.
TABLE I
light
smmxmx
or acjstxc acid solutiohs or c® (iv)
Time
(Bays)
Light
Bark
0
0.0260
0.0260
1
0 021*1
0.0255
2
0.0230
0.0253
3
0.0185
0 021*8
5
0 .0131*
0.0221
.
.
37
All titrations were made from an amber buret, and the results
Indicate the advisability of protecting the cerium (I?) solution
from light in order to minimize decomposition, When protooted from
light, the cerium (17) solutions are reasonably stable; and only
in veiy accurate work is it necessary to restaadardize the cerium
(1?) solution in a given work period*
^tab^Lit^of^Acetio Acid Solutions of Cerium in the Presence of
As has been indicated in previous sections, the rate of de~
composition of cerium (IV) is accelerated by the presence of per
chloric acid* The data in Table H serves m evidence to stg^port
these indications.
The values for the cerium (XV) concentration were obtained in
the following way*
to 5® ml* of a standardized cerium (1?) solution
enough perchloric acid was added to make the desired concentration.
Periodically 10 ml* of this solution was pipetted into an acetic acid
solution containing a weighed excess of sodium oxalate and made 1 H
with respect to perchloric acid*
The excess sodium oxalate was
determined by titration to an amperometrie end point with the
standard cerium (17) solution*
The decomposition took place in the
dark In amber flask* while the temperature was held at 27°C. The
results obtained from these determinations are listed in Table XI.
O m might expact results such as these by making an analogy to
aqueous solutions of Ce (IV).
la aqueous solutions of perchloric
acid, cerium (17) exhibits its greatest oxidizing power*
38
tm s
xi
m $ n m or acetic acid soujtxcm op c© (iv) cchtabhkc mxo4
Elapsed
Tims
(Kin.)
Hormality of Co (IV) Solution.
Homtfity
HC10.
0.5
1.0
0.7S
0
0 .01*05
0.0318
0.0306
20
0.0385
0.0272
0 .0251*
50
0.0360
0.021*1*
0.0186
110
0 .0301*
0.0190
0.011*6
of Back Titration Technique
The accelerated decomposition of cerium (X?) in acetic acid
solutions containing perchloric ©old would indicate that m excess
technique cannot be employed*
Since this technique, adding m excess
of oxidant to the solution being analysed m d back titrating the
excess oxidant after an ©lapsed period of time, Is employed extensive*
ly in cerium (I?) oxidations, further investigation was necessary.
If it could be assumed that a cerium (IP) blank, i.e., a solution
containing everything but the reductsnt to be determined, would
decompose at the same rate as the excess cerium (IP) in the sample,
then m excess technique cobid be ©sg&oyed.
To test the validity of this assumption, sodium oxalate was used.
To a weighed sample of sodium oxalate, dissolved in acetic a c i d in
the presence of enough perchloric acid to make the final solution
about 0.5 N, $0 si. of a standard cerium (IV) solution wus added.
39
the solution was then pissed in th© dark for 60 minutes.
After the
elapsed time, a neighed amount of sodium oxalate in excess over the
remaining cerium (19) was added to the solution. The excess sodium
oxalate was determined by titration with a standard cerium (19)
solution to m araperomstric end point. The asms procedure was
carried out on a blank, the decomposition of which was used to
calculate the decon^poaition of the excess cerium (19) in the simple,
the procedure was employed on two samples and two blanks and the
results are listed in fable HI.
fm m m i
KXB83S fBQMX'HB FOE DETFEMXKATOT £F ?*a3ca04
Mg. KaaC*04 Found
being Blank
Calculation
Mg. Na3C304 Found
Keglecting
Decomposition of
Excess C® (IV)
U8.6
1*S.S
1*8.9
39.3
36.9
hi .7
Mg.
taken
fhese values indicate the inability to apply 8 back titration
technique to cerium (19) oxidations, this imposes a serious limi
tation on th® applicability of cerium (19) solutions to organic
determinations, only reduct ants oaddizable by direct titration are
determinable with rail ability.
bo
8* Comparison of th© Cerium System Redox Potentials in Acetic
Acid Solutions of Perchloric Acid mid Sulfuric Acid
In aqueous media the oaddstion^redtictlon potential of the
cerium (HI), cerium (17) couple ie greatly effected toy (1) the acid
concentration end (2) the perticuler acid present in solution (28,29)„
Zh water the cerium (17) apparently forme a complex with the anion
of the acid; the different anionic complexes formed in this manner
differ considerably in their redox potentials*
In aqueous solution*
made 1 ft with respect to the various acids the cerium couple potent
tifcls vary in the following manners
perchloric acid, 1 ,70} nitric
sold, 1 .615 sulfuric acid, l.ltU} and hydrochloric acid, 1.28.
Considering only perchloric acid, the potentials wary depending on
the ©Old concentrations
1 ft, l«?Og 2 ft, 1,71} h ft, 1*7$} 6 ft, 1*82}
and 8 ft, 1 *87*
the variation of the cerium system potentials in aqueous solu
tions of the different acids and the effect of the acid concentration
suggests a comparison between th© two media, water mad acetic sold,
with perchloric acid and sulfuric acid present in the system toeing
oxidised*
ftitrle acid is not considered because of the difficulties
encountered in the presence of nitrates in acetic acid media,
hydrochloric acid was not considered since it undergoes reaction with
the cerium (17) in acetic acid to form chlorine} the formation of
chlorine is made evident by the distinct odor of chlorine from the
reaction mixture.
As has beast stated previously, the use of a calomel reference
electrode produces unreliable end non-raproducible results. Tbs
variability of results cen be attributed to the large end uncertain
liquid junction potential which exists at the Interface of the two
solutions, sad also with changes In the activity ratio of the
electrolyte os diffusion of the acetic acid occurs.
In recent years the silver-silver chloride electrode has been
employed extensively as a reference electrode, thereby eliminating
a liquid junction potential (Ik)« In an attempt to avoid the errors
of me inurement caused by having the two media, water and acetic sold,
in contact, a cell consisting of a silver-silver chloride reference
electrode and a platinum indicator electrode was used.
^hile the standard electrode potential of this reference else*
trode is known ve*y accurately in aqueous media, it is impossible to
compare this value to the one obtained in acetic acid for the follow
ing reason.
In order to assign a single electrode potential to a
particular half cell it is necessary to have a standard.
In aqueous
solutions the standard is the hydrogen electrode to which the value
of sero is arbitrarily assigned. This standard value in water may be
entirely different from that obtained in the non-aqueous solvent,
and at present there is no satisfactory method available for a direct
comparison between the two media. The potentials measured in each
medium are comparable with one another but a quantitative comparison
between the values obtained in the different solvents has no signifi
cance (Ik).
h2
*Mle It is impossible to assign a definite value to the
silver-silver eStoidio referones electrode in acetic cdd, the
values obtained through Its use clearly demonstrate the effect of
different acids and acid concentrations on the redox potential of
the cerium couple in this medium*
Since the actual position of the potential break at the equi
valence point was not of interest (only the magnitude of the po
tential of the cerium (XXX), cerium (1?) system was the measurement
involved in the study), iron (XX) perchlorate solutions were titrated
with the cerium (XV) solutions» Using this reductant on© would not
aspect the end point to be reproducible since the presence of nitrate
would present a serious interference *
In the actual measurements9 10 ml, 0.01*10 H iron (XX) perchlorate
is Introduced into a beaker containing $0 ml, of acetic acid mad©
to the desired concentration with the acid under consideration. The
iron (XX) solution is then titrated with the acetic acid solution
of cerium (XV) past the end point to the cerium (XV) concentration
where the observed potential becomes constant. This point of con
stancy is approximately, but greater than, two times the ®»mmt of
cerium (XV) necessary to reach the equivalence point of th© titration.
This constant value is taken as the redox potential of the cerium
couple in this medium,
The titration is clean cut when perchloric acid is us@d$
however, a precipitate la formed when sulfuric acid is employed.
h3
the formation of this precipitate, presumably consisting of iron (IX)
and Iron (XXX) sulfates, censes sluggishness of the reaction and an
oneatlsfactory titration*
The actual titration curves are illustrated in Fig. 3 while
f*&le XXXI liata the values observed ea the redox potentlala of the
cerium systems.
TABLE XXIX
EFFECT OF ACXD ON THE FCTMTXAl Of THE Ce (XXX), Ce (XV) GODFLE
IN ACETIC ACXD nm u
Aeid
Mid
Concentration
Potential**
4
«cJi
tmmfwr+
iHf
rt m
8310.*
0.25
988
8310.
0 .S0
999
8010.
1.0
1021*
H310.
1.5
1010.
{CIO.
2.5
1059
HgSO.
ts
806
# When sulfuric aeid ia added in excess after the potential
haa become established the observed vnLue drope to one
slightly above that observed with sulfuric acid done.
** deferred to a silver-silver chloride electrode.
As in aqueous solutions, the redox potential of the cerium system
in acetic acid varies with (l) the acid concentration and (2) the
particular acid present. While It Is impossible to cohere the
hh
n
1100 _
1. 0 . 2 5 N
HCLO4
4.
I.5 N
HCLO
4
2. 0 .5 0 N
HCLO4
5.
2 .5 N
HCLO
4
3.
HCL04
6
I.ON
- 2.5 N H 2 S 0 4
1000 —
9 00 —
80
Ll I
7 0 0 —
600 —
500
400.
12
F IG .
3
-------------------M L .
. P O T E N T IO M E T R IC
V A R IO U S
14
16
18
,2 0
C E (IV )
SOL N
T IT R A T IO N
CURVES
C O N D IT IO N S
OF
A C ID IT Y .
UNDER
1£
observed value© obtained in aqueous and acetic acid medis, it la
possible to compare the values in each medium. Whan this is done,
on© can observe that th© differences in redox potentials between
solutions of sulfuric and perchloric acids is in the same order of
magnitude regardless of whether the solvent is water or acetic acid.
Comparing the effect of varying acid concentrations on© c m see that
th© increase in potential accompanying an increase in acidity is
about the same regardless of the solvent employed.
It is possible to explain th© variation of redox potentials for
the cerium system in acetic acid solutions of different mineral
acids at various concentrations by drswing an analogy to the explana
tion offered for the same effect in aqueous media.
It seems probable
that, in the presence of different mineral acids, various anionic
complexes are formed. The particular complex present in solution
will detemta® th© potential which is observed.
By referring to tbs actual titration curves in Fig, 3, it is
possible to obtain additional evidence substantiating the statements
regarding nitrate interference* The same amount of iron (II) was
added to ©e**b solution, only th® ret© of titration varied. The
different rates of titration caused variations in the length of time
for th® nitrate and iron (II) to reset.
The large differences in
location of end points only help to illustrate the necessity of
excluding nitrate in titrations involving soetie acid solutions of
iron (H) perchlorate.
1*6
1.
Determination of Carbon Dioxide Evolution
Qualitative Detection of Carbon Dioxides Utilisation of an
Oreat type g m analyser for the analysis of the evolved gases from
the oxidation mixtures resulted only in the qualitative detection
of carbon dioxide*
In this experiment the reaction vessel containing the substance
to be oxidised was connected to the gas inlet tube of the analyser
with rubber tubing, to this solution a calculated slight excess of
cerium (If) was added while a slight vacuum was applied to the system.
After the addition of cerium (If) was complete the vacuum use in
creased by lowering the mercury level in the gas buret. When the
reaction was complete, there was a decrease in gas volume when the
gas was passed through the potassium hydroxide,
Subsequent attempted
combustion In m oxygen atmosphere resulted In the formation of no
gas which was taken out by potassium hydroxide, This Information
indicated that carbon dioxide was the only volatile substance which
was formed in the oxidative reaction.
Before conclusions could be drawn concerning earbon dioxide
evolution mod stoichiometry of the reactions, the actual msouat of
carbon dioxide evolution had to be determined, This measurement was
conducted with an apparatus schematically illustrated In Fig, h.
Acetic sold containing the reluctant in the reaction vessel
was first saturated with carbon dioxide, Nitrogen was then forced
through the system for two hours, or until no more carbon dioxide
)K
(
•
'i
i
•
i
CD
t
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i
i
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j
1
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11
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cr:
z>
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CD
UJ LU
D IO X ID E .
1
D E TE R M IN IN G
1
t
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<
APPARATUS
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CA RBON
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<3
*« ^
f>
to
5
O
to
8
8
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VA
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a
*3*3
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PA
PA
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*A
a
*3
a
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CM
CM
CM
on
^13
°.°.
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ua
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a ^
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H
3#
> *
iI
Acetone (2)
!
S
wH
's.*
Acetone (l)
*
(3)
Of
Bovaldftty'**
&
*
sO
0.2 s£L,
%
°>
*
«.
(2)
ft
VA
-3ft
o
VA
Os
vO
*
Bontaldfttydft
o
VA
Os
$3.6
-3
•
U8.3
fA
€K
•
$0.3
\0
3k.9
59
« CM
ps^
-a.
1
60
Other polyols, such as micros® or tart eric acid, present m inter**
ferenae whether acetic anhydride la present or absent*
In these cases
It is believed that insufficient acetylstion has occurred to slow the
oxidation enough to prevent the interference.
If an attempt is made
to increase the amount of scetylation by heating th© solution in th©
presence of acetic anhydride and letting the solution stand at m ele
vated temperature for en hour, there is still no end point.
Apparently
sterlc hinderenoe of th© molecules is sufficient to prevent adequate
acetylation which would make the determination practical.
In the light of the observations noted for polyols, it is diffi
cult to reconcile the effect caused by the action of ethanol in a
medium containing acetic anhydride,
it seems possible that in the
presence of acetic anhydride m ethyl ester of oxalic acid is formed.
The behavior of th© galvanometer during titration supports this specu
lation,
Oxidation proceeds rapidly at the beginning of the titrstlon
and slows to m almost negligible rate.
If the solution stands, how
ever, th® next addition of cerium (I?) is consumed repldly, indicating
trsnseaterific©iion, Possibly an equilibrium reaction of this type
wey be establishedt
E.C - C
v -<
C - OH
'o
0
*
i
0
c-oh
Cv
tt
se^oooa +
y
10
0
Either anhydride now could react with the ©tlyl alcohol to form an
ester.
An alternative suggestion might be the disproportionetion of
61
oxalic anhydride with the formation of csrbon isonoxlde and carbon
dioxide (10)* This suggestion Is discredited by the value obtained
for oxelste in the other determinations in the presence of acetic
ifflfydflds.
Fortunately, the reaction of cerium (IF) with ethyl alcohol pro*
coeds sufficiently slowly to permit a direct titration of ox state in
the presence of acetic acid without the necessity of acetyletion of
the alcohol* The results obtained in this titration are excellent*
In general the results obtained for the determination of sodium
oxalate in the presence of a wide variety of oxygenated substances are
good*
On the basis of the values, it would seem justifiable to state
that the selectivity of cerium (IF) oxidations are improved in the
acetic acid medium over those in aqueous media*
0*
Sodium Hasoxalsta
Sodium mesoxalate (Sodium dihydroxymalonat©) has received brief
consideration in the studies concerning carbon dioxide evolution; but
t M s section is devoted to a detailed discussion of the direct tlbre*
tloa of sodium mesoxalat© with acetic acid solutions of cerium (IF) *
Under the conditions employed in the titrations, this reagent Is one
Of the more satisfactory chemicals determinable by the osddimetrio
technique*
Sodium tnesoxalat© is easily prepared by alkaline hydrolysis of
dilu^m a«
vO•
in•
P~
CM
-3
CO
-3•
O
-3
in*
GO
-3
vO
•
m
-3
H
•
Os
-3
CM•
r-
in
vO
•
co
-3
CO
cn
CM
O
CO
•
5*
-3
cn
c*~•
VO
CM
H•
cn
-3
vO•
m
-3
in•
NO
cn
s
O
SS
p
5
O
P,
1
a
a
» c
T3
fS
©
0
o
ss
5a ^5
§
S3
Sss
3©
3 o
o
m3
~3
cn
CM
ss
©
M3
p—
CM
CO
p
in
U 0
•$ O
t
a
TJ
o a
3c;34s
S838©
P3
m
ON
m
|
a
*
£
i 1a
a
i
a
«H
83
o
H
m
0
0
o
S3
O
SB
©
«SI
o
M
6*
&o3
aB
5
£-«
O
Si
«W»
°£
•P T»
K
O
•
EO
€ B
O O o c o o o o• o•
in in • ED - G - OH
IE - OH
0 • C * OH
9
.
76
The acetic «cld solution of cerium (I?) contains another oxidant,
nitrate 9
»ay conceivably set as an interference under the con
ditions of the titration, Tide interferene©, if it were present, could
eaqplain the uneven number of electrons transferred per molecule of
malonie acid in the oxidation process.
In order to eliminate this point
from consideration, %m grams of lithium nitrate were added to the acetic
a d d solution of malonie acid made 1,5 N with respect to perchloric acid.
This solution stood for two hours and then was titrated in the usual way.
Ho difference was observed,
Tory little interpretation of the results is possible because of
the unreliability of the technique, Nevertheless an excess procedure
was attested in the determination of malonie acid. The procedure
adopted was the same as that used in the oxalate titrations. The malonie
acid solution containing the ©xeesa cerium (17) stood for one hour end
the excess cerium loylng the
excess technique and permit the reaction to go to completion; but on the
basis of the whole, even number of electrons transferred one might expect
* stoichiometric reaction.
Subsequent work does not support this essuaqp-
tion and inability to obtain reproducible values is attributed to side
reactions.
Only carbon dioxide is positively Identified as a product of the
oxidation with all of the carbon dioxide being derived from the solvent.
In addition to carbon dioxide there ®r© good indications that formic acid
is formed in a mol® to mole ratio; and inconclusive results indicate
th® presence of some aldehydes.
8JU
P. Miscellaneous Oxidations
This section Is devoted to the substances which received & super
ficial examination and which were found to be Indeterminable by a direct
titration with acetic acid solutions of cerium (IV) prepared from ammon
ium hexanitratocerate (IV) . In choosing the compounds which were sub
jected to a cerium (IV) oxidation two different approaches were employed*
(1) Those materials were selected which, when titrated with a cerium
(IV) solution,, might furnish an insight into the oxidation process
threw# which the materials which received detailed attention p*ss.
(2) A variety of substances were used so that a clearer picture of the
selective action of cerium (IV) oxidations in this medium could be ob
tained,
All of the compounds were subjected to cerium (IV) oxidation under
conditions identical with those employed for th© titration of malonie
acid, but none received as extensive m investigation.
1, Derivatives of Malonie /old
In the study covering malonie acid, it was considered essential that
eaters of malonie acid and substituted malonie acid should receive atten
tion for two reasons.
First, it might be possible to work out e determina
tion for these materials.
Second, it might furnish information covering
the cerium (IV) oxidation of malonie acid.
Potassium ethyl melon®!® (18) and methyl malonie acid (1) were pre
pared from redistilled diathylinalcmate according to accepted procedures.
85
Both diethyl and monoethyl malonste ere oxidised, but much nope
slowly then the ecld. There were mum indications that transestsrificatlon is taking place prior to oxidation. The mthylmelonic acid also
is oxidised slowly.
With th® eaters md th® substituted malonie scid, the reaction takes
place too slowly for a determination to be made by the direct titration
with the cerium (IV) solution. These observations suggest that both
carboxyl groups and the active methylene group must be free in order
for oxidation to proceed at a favorable rate,
2, Methylene Placetate* Methyl Formate. Methyl Acetate, and Ethyl Acetate
Any one of these eaters could conceivably bs formed in either th®
malonie sold or citric acid oxidation; md for th$t reason, an attempt
was made to determine each with cerium (IV), Th© methyl formate, methyl
acetate, and ethyl acetate were obtained commercially while methylene
diaeet&te was prepared by the action of poetic anhydride on paraformal
dehyde (20),
The methylene diecetgt© is oxidised much too slowly to be determined
by a direct titration, while methyl formate, methyl acetate, and ethyl
acetate appear to be stable in the medium.
In the Investigation of methyl formate an interesting observation
w®s made which is utilised later as a qualitative test for the identifi
cation of methyl formate. An acetic acid solution, 1 K with respect to
perchloric acid, containing 57.3 mg. methyl formate is permitted to
stand In a glass stoppered flask for 1.5 hours. At the end of this time
enough sodium acetate is added to furnish an excess of about 1 g, over
86
that necessary to neutralise the perchloric acid. An excess of lead
tatra~aeetate is then added to the solution and the mixture left in
the dark for 1 hour* After this reaction* the excess lead tetraacetate
is determined iodlmatrlcally as described previously. This me©eurement
showed that about £0$ of the methyl formate had reacted. Presumably the
load tetra-acetat© oxidation takes place on the formic acid produced in
the reaction*
H-S-OCHg
♦
HaC-C-0H
this reaction is offered here since it is used later. Ro claims &*e made
concerning quantitstive application but these observations are presented
to show a method for the qualitative detection of methyl formate which
is applicable in a medium of this type.
Th® attempts to use cerium (IV) in the oadd stive determination of
those esters resulted in failure. Using the results, however, these
materials c m be eliminated as possible intermediates or end products in
a stoichiometric reaction of the confounds studied previously in greater
detail*
3. Oxalacetic Acid and Pyruvic Acid
These reagents could conceivably b© formed in the oxidative reaction
of either malonic acid or sodium mesoxalata. In addition these materials
serve to illustrate the reactions of «<
co ^
CM
CM
oo r;
CD 1X1
< O
O
Lu
CJ
in
92
length m a lesser one of the oxidation system.
On this basis it nay
be said that the oxidation of citmxnie acid is incomplete with the
addition of four moo* cerium (IV) per millimole cinnamic acid. Attack
of the double bond is indicated by tfes appearance of what seems to be a
strong absorption band at about 2$h am. Below 252 mu the solutions
became opaque and the exact location of this lower absorption band la
unknown* If the oxidation process results in complete rupture of the
double bond a product which wight be expected is benzoic acld# It is
quite obvious that benzoic acid is not a product formed in appreeijfcle
quantities when reference Is made to the curve obtained with pure benzoic
acid dissolved in the same medium as the oxidized cinnamic acid.
In the hops of being able to obtain a procedure which could be
utilized in the direct oxidimetrie titration of cinnamic acid, the per*
chloric acid concentration of the solutions being titrated were varied.
Concentration ranges of from 1 to h H perchloric acid were employed but
in m case was It possible to obtain m and point,
Gyclohexsne and m&leic acid are oxidized but at a slower rate
throughout the titration than the corresponding oxLdstlon of cinnamic sold.
While b determination of these unsaturated molecules was not realized,
these observations show that double bond unsstursiien is attacked by
cerium (IV) at an appreciable rate in this medium,
12, 2.5^Dimethyl^3^Be3gm®>>2, 5~diol
this reagent, obtained commercially, appears to be quite stable in
the oxidizing medium, this helps to illustrate the indication of greater
93
stability of triple bond unsaturations toward cerium (17) oxidation then
a double bond wnsataration in the acetic sold medium,
13* 2-Mercaptobeirathiaaol
fids meresptan exhibited a eurpriolngly high degree of stability in
the oxidation medium.
Ho attempt is made in these examinations to el aim a thorough investi
gation of the oxidation possibilities of cerium (17) in acetic eeidj but
a nldo range of bond types received attention.
In these studies none of
the reagents ware found to be determinable by the oxidation tltrationj
but by the proeess of elimination some possible end products or inter
mediates are eliminated as possibilities in the oxidation scheme of the
four chemicals investigated in detail.
9b
DISCUSSION OP MECHANISM
The information collected in this mark provides a basis for Inter
esting speculation concerning the mechenism of cerium (IV) oxidations In
this medim,
For the mechanistic considerations a certain mount of
information is available which is applicable to all of the reactions
studied in detail.
(!) the use of 1-cerbon-lit acetic acid Indicates
extensive m d &toichlometrie participation of the solvent in the reac
tions,
(2) Qualitative tests suggest the presence of peroxyacetic acid
in the decomposing cerium (XU) solutions.
(3) Only a limited masher of
compounds undergo reaction at a sufficient!/ rapid rate to permit a
direct titration.
By reference to mechanistic studies in srster, it is possible to
derim infoxmtion which may be spiled to cerium (XU) oxidations in
acetic acid,
In aqueous media, It has been proposed that ionic oxidising
agents react in the following manner with oxygenated reductasits (6,13) *
Using iron (XXX) as
the oxidantacting on anorganic molecule containing
oxygen which has at
least on®pair
of unshared electrons*
. C • o;
+ Fo+**
-C - O'
♦
Fa*4
. C * O'
♦ fa***
-0-0
♦
Fa44
The oxidation is probably preceded by an Intermediate complex form
ation (7,8). The rata of oxidation Is a function than of the oxidizing
power of tbs oxidant and Its ability to fora tbs Initial complex.
95>
fto® evidence collected in this work is not sufficiently complete to
propose a definite Mechanism; but by referring to studies in aqueous
medic, it la possible to present a scheme which will explain the results
found in tiiis work*
A.
Oxidation of Sodium Oxalate
Under the conditions employed in the determination of this reagent,
the oxidation is essentially instantaneous * the reaction proceeds with
the consumption of two meq* of cerium (IT) accompanied by the evolution
of two millimoles of carbon dioxide per millimole oxalate.
Only cartoon
dioxide could be detected m a product of the oxidation, sod carbon-lit
studies indicate extensive and apparently stoichiometric participation
of the solvent*
A measurement of csrbon-lh dioxide indicates that the
reaction proceeds involving acetic acid m d oxalate in a mole for mol©
ratio*
In order to eex^&y with these observations It would appear necessary
that an unstable intermediate must be formed in the oxidation scheme which
involves the solvent and the oxalate in equal molar proportions*
Definite proof is lacking but a reasonable explanation might be the
formation of a mixed peroxide which would undergo further decomposition
accompanied by an intramolecular rearrangement, this might be depicted
in a scheme similar to the following*
0
* C0a + C 0-j
OH
96
Am intramolecular decomposition of this type would ccsaply not only
with the results obtained for cerium (IV) consumption and carbon dioxide
©volution, but would also explain the inability to detect © combustible
gee.
If tlie decomposition of the proposed intermediate would proceed
with the formation of a free methyl radical, methane would be expected
as a product ©f the oxidation (19,23,35,36)*
In addition to an intramolecular rearrangement of the type mentioned
it would be conceivable that a modified Baeyer~Villiger reaction might
explain the results (3)«
A generalined Baeyer-Villiger Rearrangement is:
* & * • ♦ R»C©aH
9
HC -OH1 4 R"CO*H
A Baeyer^VHliger Rearrangement modified to fit the oxalate systeir is:
If this type of a rearrangement were operative then methyl formate
would be a reaction product* Whom applying the test for methyl formate,
described previously, the results were negative. This indicates that
if this reaction does tefee piece, it is minor in extent.
wMlft the evidence is not conclusive it seems possible that the
proposed intermediate might be formed and that its decomposition proceeds
in the manner shown.
91
B«
Sodium Hosexalsfce
As in the titrations of oxalate, the oxidation of this reagent
takes place essentially ijurtaneously. The oxidation requires four milliequivalents cerltm (X?) and la accompanied by the evolution of three
mUltmoles of carbon dioxide, la the carbon dioxide evolution studies
utilising carbon-lb, extensive participation of the solvent is indieeied.
Apparently acetic sold eaters into the reaction in a stoichiom®trie
manner.
A molar ratio of one carbon dioxide derived from the solvent
per eno of mesoxalate oxidised is obtained through the use of this tech-*
niqae.
Again the evidence la too Inconclusive to propose a definite mechan
ismj however, it would seem possible that the initial step in the oxi
dation step involves oxidative decarboxylation. If this takes place,
the molecule remaining would be oxalic add which could be oxidised as
in the scheme mentioned previously.
Clear out evidence supporting this type of mechanism is lacking but
eajploying m eaq&snaiien such as this would coi^ly with the observations:
(l) Ho combustible gas is detected.
(2) The reaction is somewhat slower
than the corresponding oxalate oxidation.
(3> The studies employing the
csabof*»lh tracer technique show that, in the oxidation process, the sol
vent participates in a stoichiometric manner with one mole of acetic
acid being used per mole sodium mesoxal&te oxidised.
(b) The reproduci
bility and stoichiometry of the reaction are satisfied.
98
Citric Acid mud Kalemie A d d
The available date are not sufficient to offer a reasonable explana
tion for the oxidation of these materials. Apparently the re set!one are
Wit# conplex. The complexity might he ejected if the proposed staeohan**
lass in aqueous media mentioned praviously takes piece in the acetic acid
meditsn* Using raalonlc add m an example t
v
<«pr w a s
I
0 * C « OH
0'
*2
H *" 2
C
0 » C - OH
„
+ 2Ce(XV)
*-
COH o h
0 * C - OH
wr
♦ 2CeIII
* «♦
H
The resource possibilities of the free radical may stabilise the
r die el sufficiently to permit polymerisation. If this Is the esse one
could expect two types of bonds to he formed preferentially In the polymer
each of which has about the same bond energy!
These possibilities, if they exist, could e^lain the inability to
isolate clear cut products and the fast that m end point is reached
which corresponds to the transfer of m fractional number of equivalents.
It does not explain the evolution of two millimoles of carbon dioxide
both of which come from the solvent.
99
fhe lack of more information makes any more speculation pure guess
work.
T#iat hoe been said concerning malonlc acid could be repeated in the
explanation concemiiig the oxidation of citric acid. the increased com
plexity of the molecule # however, would lesd one to suspect an even
wider variety of reactions* Because sufficient data are not srfeil&le,
it is impossible to drew conclusions other than those which would be
exactly comparable to the speculation concerning malonic acid*
100
mmm
Initially ibis work was begun to investigate possible analytical
applications for which acetic acid solutions of cerium (17) could be
used and to collect data which would sid in the ellucidetion of the
oxidative Meehan!®® through which the reactions proceed in this medium,
in general, these objectives have been accomplished as Is evidenced by
the results produced in the investigation.
Acetic acid solutions of cerium (I?) were prepared from ammonium
hexanltratocerste (17) since investigation shewed that higher concentre-*
tions of oxidant were obtainable in acetic acid through its use then
with other salts. An antperometrlc technique employing two active
electrodes was used almost exclusively in following the course of the
titrations. This procedure for detecting the equivalence point was
adopted in preference to potantiometric methods because of certain in
herent difficulties encountered with the reference electrodes in this
non-aqueous medium.
The following observations were noted In the investigationt
(1)
Acetic acid solutions of cerium (17) prepared from ammonium
hexanitr©tocerate (17) ore reasonably stable if stored in the drrkj only
in very precise studies is it necessary to rest endsrdise the solutions
during a given work period.
If the solutions are stored in light or if
a mineral acid is present, the rate of decomposition of cerium (17) is
accelerated to m appreciable degree.
Id
(2) It is possible to standardise cerium (1?) solutions with
primary #fc«**d*rd grad© sodium oxalate, this reagent fulfill* the re
quirements necessary for e standard reductant in this medium.
In ad
dition to sodium oxalate, iron (n) perchlorate exhibits the prescribed
requirements for a standard reluctant tilth one exception, nitrate pre
sents a serious Interference,
Even though Iron (IX) perchlorate solu
tions can not be used for the determination of cerium (IV) in the pres
ence of nitrate, they c m be used to good advantage in the determination
of other oxidants In the absence of nitrate.
Evidence is offered de
monstrating the feasibility of employing this reagent in the analysis
of acetic a d d solutions of sodium permanganate and chromium trioxld©.
(3) ployi ng acetic acid solutions of cerium (I?), it is possible
to deterdoe sodium oxalate or sodium mesoxalate in the presence of ©
wide variety of oxygenated materials.
On the basis of these results,
It seems justifiable to claim increased selectivity ©f the oxidant in
this medium* Malonie acid end citric acid are determinable by a direct
oxidimetrlc titration, fhss® last oxidations ere not entirely satis
factory sines empirical m m s must be employed in detecting the end
point.
(h) In the oxidation process of these materials, carbon dioxide is
evolved in a stoichiometric manner,
^ploying acetic acid which is
tagged with csrbon^lU in the carboxyl group, extensive solvent partici
pation in the oxidation process is shown. Per mole of reluctant, the
values for total c arbon dioxide ©volution and amount cf c erbon dioxide
102
derived from the acetic a d d for the individual reductants are*
oxalate# two god ©nej malomlc acid, two and twoj sodium
sodium
m e a o x a l a t e
, three
and ©nej and citric sold, three and three,
(5) A* in aqueous media the redox potential of the cerium couple in
acetic sold Is dependent m the type of mineral acid present and con*
eonir&tlon of that sold* Perchloric acid provides the highest redox
potential. The variation of the potential in the presence of different
adds suggests that complexation takes place in this medium.
these accomplishments show partial fulfillment of the broad objec
tives established at the beginning of the Investigation! however, during
the course of the study, several other problems presented themselves i
(1) A more eezqplete investigation of iron (II) perchlorate to
realise its eventual possibilities in this medium,
(2) Farther study concerning the employment of sodium per
manganate in acetic acid,
(3) the extension of cerium (1?) oxidations to aubstmces other
than oxygenated materials.
(h) stills ation of other tagged mclocules to farther ellucidate
the oxidative machsniara.
103
irfERAft?R2 CITED
1* Adam©, R. and Johnson,
B, "Laboratory Experiments in Organic
Chemistry,n p. 147 # The Macmillan Company, How York, (19U9).
2, Allen^B^H. and Witaeaaan, B, «?.,
ion. Chan, So©., 6g, 1922-7
3. Baeyer, A. m d Villiger, V., Bar., J&, 3625 (1899).
it* Boesaken, J. and Jacobs,
5. Cano, W* S.,
Bee. tree. ©Mm., gg, 80L-1L (1936).
Am. Obam. So©., 6J, 1976-62 (19it6).
6. Oonent, J,
B „ Cham. Bov., j[, 1
(1927).
7. Coaant, #*
B.m d Aston, J, 0,,
J. An, dwn. So©., gQ,2785(1928).
6, Conani, J,
3.,Aston,
it# &>7 (1930).
0,, m d Tongbary, C. 0., J.Am.Cham. So©.,
9* Conrad, S., Bar., g£, 1819 (1902).
10. Englmd, w* B, laid Maekanaie, H. A. s., J. S. African Cham, mat.,
I, 1U7-59 (19it9).
11. Fieser, L. F. "Sbgjeriments in Organic Chemistry,* pp. l*36-k0, D. C.
Eastb m d Cospany, Bow Tork, (l9hl) •
12. Foeiar, L. M.
and Payne, J. I., J. Am. Cham, So©., 223-5 (I9ltl)•
13. Oilman, Stay. »€rgml© Chemistry An Advanced Treatise Vol, IF."
pp. 1120-12)5, John Wiley mad Sons, Inc., Hew Tork, (1953).
lh* CEsaatone, Samel, *An mtrodnction to Klactrochemiatry,11 p. 2hh,
B. Fan Hoatrand Goagiany, Inc., Haw Tork, (I9i*2).
35, Qroenspan, f.P. and I t e M U r , P. 0., Anal. Che®.,
20, 1061 (19l8).
16. Qraeimood, F.h „ J. Qrg, Cham., 10, i&fc~l8 (191*5),
17. Guardi*, 0, C,, Afinldad, J&, 289-S& (1950).
18* f&slm&etfcOB, V* J „ "Reactions of Organic Compound©,« p. U18,
Longaans, Green and Co., Haw Tork, (19U8).
10k
19. Kharasch, H. SFriedlander, H. N. and Urey, W. H., J.Qrg.
16* 533-42 (1951) and Receding papers,
’
Chem.,
80. Khoevenegel, von E., Ann., 1*02, 127 (19lU).
21. Mosher, V, A. and Kehr, G. L,, J, Am. Chera. Soc., j£, 3172(1953).
22. Perlin, A. S., Anal. Chera., 20, 1053 (195U.
83. Haley, , 1-52 (19li9)*
32. Thompson, R, B. and Chenicek, J, A., J. Am. Chero, Soc., 69 . 2563
(19H7).
33. fomecek, 0, and Efeyrovsky, A,, Collection Czech. Chero. Comroon*, 1£,
997-1020 (1950)*
3I4, fomecek, 0, and Faleha, J., Collection Czech. Chera. Coromun., 16 - 1£,
113 (1951-52).
35. Waters, W, A,, f,fh© Chemistry of Free Radioals,w pp. 2U5-7,
Clarendon Press, Oxford, (191*8).
36. Waters, W, A*, "he Mecanisroe de L*oxydation," pp. 101-9, R. Stoops,
Id., Ruitieme ConseH International de Chlroie Solvey, Brussels
(1950).
J7 . Willard, H, H., and Xoung, P., J. Am. Chero. Soc., |2, 132 (193°)*
105
APP^OH 1
Summary ot Oagrganated Substance® Subjected to Cerium (IV) Oxidations
Determinable by Direct Titration
%dro<2uinon@
Sodium Oxalate
Sodium Mesosjdate
Malonie Acid*
Citric Acid*
Enactions Proceeding Baldly at First but Slowing Down During Titrations
Tartaric Acid
Ethylene C&yeol
C&ycerol
Acetyl acetoncte
Sucrose
OjesBlscetic Acid
Pyruvic Acid
factions Proceeding Slowly Throughout the Titrations
Methylene Dtscetat©
Fomaldebyde
Bensaldelyde
Btjyl Alcohol
MetliyX Alcohol
Cinnamic Add**
Halle Acid
Cycloh®3B*na
2 , 5-Dimethyl-3-Hbsyne-a^-Di^
2 Marc ^tobensthls&ol
P-aminofoenssolc acid and fluorene
Stable Materials
Methyl Formate
Methyl Acetate
Ethyl Acetate
Succinic Acid
Formic Acid
Benaoic Acid
■-J1u"ir¥'_jfei'rr% r 3r saMsfectory
*» Reacts at « rate approximating a Favorable titration.
106
mmxix 2
Calculation Used for intimating
Kinimura Amount of CHgC14^!? Hooded
jjfgdyfgjgifrl& In order to be statistic &Lly accurate the final count
m m % be at least six time# background or at least 21*0 counts per
minute or k*Q counts per second.
i^aumotlorai (1) flow counter is 10* efficient.
(2) The acetic sold
and reductent react in a mole to mole ratio.
One mlllimsrie (fey definition) » 3,1 x 107 Disintegrations per
second.
work.
/t least U.O counts per second are necessary for accurate
Assuming IQ* efficiency of the counter, kO disintegrstions
per second are necessary.
ho
_
jTTaTIB^ isillicuries are needed in each sample,
Saw$Le eisss are in the order of 0.2 millimoles of redactant which
are dissolved in $0 ml. or 875 millimoles of acetic acid.
Using the original assumption of a reaction involving mole to mol©
ratio of acetic a d d to reductmt this expression can be set vpt
f y '
xlgr
a®
X ^
• 0 ,1 ,7 3 x 10~ a ■“/•“ P1®
Since 20 sables ere to be collected the minimum amount of material
is shout 0.1 me.
107
mmsxx 3
Sajfiple Calculation for Determining
ilm Itxmlvmm% of Acetic A d d Doing Carben~l2i Dioxide
Initial ut, sodium exiXgte
52*6 ag, • 0*392 nllll&oXee
Total ift* 'precipitated laOO^
XSh*0 ag*
Wi* SaC03 taken for counting
50*0 sag*
Set counts per nitrate on sample
£73*5
Hot counts per a&mte per ssillimole sodlvm oxelat©
2150 counts per d m t e
Going through the mm® procedure nith the acetic aeld solvent after
combusting m d collecting the carbon dioxide efc SaCI3
« 1*06 mUlimclee CO* from acetic mid
«&Sm 3