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HTHS

“SHE ABSORPTEON 03“ THE
ALPHA. CEL’E‘A AND GAMMA
ESOMERS OF
HEXACEQLCROCYCLGHEXANB
B? ACNV‘ATED fixLUMENA

“{‘imgix for 1113 Dsgroa of M. S;

MICHIGAN 3?.ATB. COLLEGE
Lewis grederéck Gfibcrt

W49

This is to certify that the

thesis entitled

"The Adsorption of the Alpha. Gama and Delta Iso‘ners
of Emchlorocycohexane by Activated Alumina'i.

presented by

Lewis 1'. Gilbert

has been accepted towards fulfillment
of the requirements for

ILS. degree in 2111316111 Chemistry

AT '
Major professo

Date MM

 

THE ABSORPTION OF THE ALPHA, DELTA AND GAMMA ISOMERS

OF HEXACHLOROCYCLOHEXANE BY ACTIVATED ALUMINA

By

Lewis Frederick Gilbert

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

MASTER OF SCIENCE
Department of Chemistry

1949

GMTRY DEPT.

Tam
e 465

ACKNOWLEDGFENT

The author wishes to thank Doctor D. T. Eling
for his aid and guidance, without which this work
would not have been possible.

****$*****
#**##***
******
##1##

*1!

t

TABLE OF CONTENTS

Page
IntrOduCti-OnOOOOOOOOOO0.0.00.0...OOOOOOOOOOOOOOOOOOOOOOOO 1

Experimental

ChomjncaJ-SOOOOOOOO0.0.0.0...OOOOOOOOOOOOOOOOOOOOOOOO

ApmmtuBOOOOOOOOOOOOOODID...OCOOOOOOOOOOOOOOOOC...

(ANN

ProcedurOOOCCOOCOOO00.0.0000...00.0.0.0...000......

Results
Adsorption Data. TabIOS.........o..................o 6
Adsorption Isothems..................O............ '

Discussion
Pure Isomer Adsorption............................. 11
Mixed Isomer Adsorption..;......................... 13
Correlation to Chromatographic Data................ 13
Gamma Isomer Conversion............................ 14
Experimental Precautions........................... 16

CODClusioDSOOOOOOOOO0.0...00.0.00...OOOOOOOOOOOOOOOOOOO.. 19

ReferenOGSOOUOOOOOOOOOOOOO.0.00.0.0...OOOOOOOOOOOOOOOOOOO 20

INT RODU CT ION

The complex molecule of hexachlorocyclohexane was first prepared-
by Faraday in 1825 (7) but few investigations were carried out on the
compound until 1943, when Thomas discovered the insecticidal property
of this chlorine substituted benzene. (3) Through this lack of in-
veetigation very little was known about the chemical and physical
properties of the molecule. Since 1943, however, considerable effort
has been directed toward investigating a number of these properties,
not only for its insecticidal use but also as a study of the chemistry
of a complex molecule.

Hexachlorocyclohexane is prepared by the chlorination of benzene
in the presence of light. 'It is carried out by passing chlorine gas
through benzene that is illuminated with ultra-violet light. (2) (6)
There has been much speculation and many investigations concerning
the structures of the six isomers of this compound. (3) .As yet only
the structure of the beta isomer has been determined. (1) (4) However,
it has been concluded that this compound has the same isomers and struc-
tures that are possessed by inositol, which is hexahydroxycyclohexane.
(3) (5)

The purpose of this work is to investigate and determine the
adsorption isotherms of some of the individual isomers, singly or
added in mixtures. From.these we can gain not only physical data for
the compound but also can reach some conclusions about the individual
isomers. At the same time this data can be correlated to chromato-
graphic data of these isomers from previous work by Saur (6) and a

better understanding of chromatography can be attained.

-1-

EXPE l 1“!qu AL

Chemicals

Acetone - J. T. Baker or Merck and Co. - was used without further
purification.

Alumina - .Aluminum Co. of America, E-20 grade, 80-200 mesh - was
activated at 2500 C. for four hours and was cooled in a
dessicator using calcumn chloride as drying agent.

Carbon Disulfide - Baker's Analyzed or Mhllinckrodt Chemical'works
- was used without further purification.

Hexachlorocyclohexane Isomers (Alpha, Delta and Gamma) - were sup-
plied by Niagara Chemical Division, Food machinery and
Chemical Corp., Middleport, N. Y.

Hexane ~- Eastman Kodak Co. - commercial grade of hexane used
'without further purification.

Skelleysolve "B" - Skelley Oil Co.

Apparatus
Becknln Infrared Spectrophotometer, Mbdel IRr2. The instrument was
cooled to 25°20.4° C. by water. The cell was the sodium.chloride

type. Cell thickness was approximately 0.28 mm.

Procedure

In general a known amount of the isomer in solution is placed
in contact with a known amount of adsorbent. After a given period of
time the solution is analyzed to find what amount of isomer is still
in solution. The difference represents the amount which has been
adsorbed. Due to the high volatility of the solvent, hexane or
Skelleysolve "B", closed systems were used for the adsorption process.

The isomer or mixture of isomers, as the case may be, was dis-
solved in the solvent, hexane or Skelleysolve "B". A saturated solu-
tion was prepared and was then diluted by adding 50 ml. of the solvent
to 200 ml. of the solution. This prevented any precipitation of the
solute due to small amounts of evaporation during the preliminary work.
Small amounts (5 to 7 ml.) of the solution were placed in 10 m1. glass
ampules which had been weighed and contained weighed amounts of acti-
vated alumina. As each ampule was loaded with solution a sample of
the same solution was placed in a weighed 10 m1. volumetric flask for
analytical purposes. Immediately after the ampule was filled it was
sealed by an oxygen torch. The filled ampule was then weighed to de-
termine the weight of solution. The weight was also taken of the 10
m1. volumetric flask to determine the weight of the sample taken for
analysis.

The ampule was then placed in the stirring apparatus for a period
of 72 hours, the time necessary to reach equilibrium in this system.
The equilibrium was attained in a constant temperature room which also

maintained a constant humidity. The ampule was then broken and the

solution was filtered through No. l ashless filter paper. The fil-
trate was caught in a weighed 10 m1. volumetric flask. This flask
with the filtrate was again weighed to find the weight of the fil-
trate.

The two 10 m1. flasks, one containing a sample of the original
solution andone a sample of the solution after adsorption, were then
placed under vaccum and evaporated to dryness. The residue was redis-
solved in 10 m1. of carbon disulphide for analysis. The analysis was
made by means of the infrared spectrophotometer by a method devised
by Daasch (7) and modified by Saur (6). ,

Using the following mathematical procedure adsorption values

(x/m) were obtained. The x/m was evaluated as:

x/m = weight of isomer adsorbed
weight ofadsortent

 

1. To find the weight of the isomer adsorbed (x):

x 8 original weight of isomer in solution - the final weight
of isomer in solution

a) Original weight of isomer in solution in contact with
E g. of adsorbent (wg)

W6 3 '1 x wz/Ws
where:

"l _ weight of solution in contact with the
alumina

weight of sample of original solution
(in 10 m1. flask)

e?
I!

w weight of isomer in sample (w5) by

infrared analys is .

b) Final weight of isomer in solution at equilibrium (w7):

 

w7 = ("l-We)! 1"5
'4

where:

weight of solvent in the sample of equilib-
rium solution

'4

weight of isomer in sample of equilibrium
solution (of solvent weight w4)

1'5

weight of isomers in the solution in con-
tact with the alumina (this is the weight
of solvent in the original solution in
contact with the alumina)

of
u

c) Weight of isomer adsorbed (x):

‘

X I We - W7
2. Concentration of equilibrium solution (in gravimetric terms):

conc. : ws

"4
3. Weight of adsorbent (m) is found by direct weighing.

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- “L I .0 .fi «L
2" ° ' /”
0.005 0.010 0.015 0.020

Equilibrium cone . -g . lower/8 . solvent

F1 . 1 Adsorption isotherms 0
ch orocyclohexano. (1) Delta,

1‘ e ismers of Hexa-

 

 

 

 

O
O
0‘

 

x/m -g. adsorbed/S. adsorbent

 

(2)
'0»

 

 

 

 

 

 

 

 

 

 

 

10/0
Dal-0—
0.002 0.004 0.006 0.008

Equilibrium conc.-g. isomer/g. solvent

Fig. 2 Adsor tion isotherms of isomers in isomer
mixtures. (1 Delta, (2) Alpha.

DISCUSSION

In Figure 1, even though all of the points do not give the desired
smooth curve for an adsorption isotherm, there is a definite tendency
of a decided trend. Mbst of the difficulties can be attributed to the
low solubility of the isomers in hexane, which caused a considerable
portion of the work to be with low concentrations. This 10W'solubility
is a characteristic property of the isomers in most solvents as shown

in the work of Slade. (s)

Solubility of Isomers at 20°C (3)

Solubility g./1OO g. solution

Solvent Alpha Gamma Delta
Acetone 15.9 43.5 71.1
Benzene 9.9 28.9 41.1
Carbon Tetrachloride 1.8 6.7 3.6
Cyclohexane 1.4 4.6 2.7
Ethyl alcohol 1.8 6.4 24.2
methyl alcohol 2.3 7.4 27.3
Pentane 0.9 2.2 1.6

The isotherms of alpha and delta isomers represent the tnue adsorp-
tion of each by activated alumina, while the isotherm for the gamma iso-
mer represents not only the adsorption of the gamma isomer but also the
conversion of this isomer to the delta isomer. Due to this conversion
the isotherm is higher than.the true adsorption isotherm would be for
this isomer. However, the isotherm.represents the removal of gamma

from solution by alumina and'will be useful in correlating this data

-11-

to chromatographic data. The subject of the gamma isomer conversion
to the delta isomer while in contact with alumina will be treated
later in this paper.

It should be noted that the alpha isomer isotherm passes through a
maximum and at higher concentrations the x/m value decreases. This
action can possibly be accounted for by negative adsorption. This type
of adsorption is not uncommon and takes place with many compounds and
adsorbents. (8) The theory for negative adsorption is that the solvent
is adsorbed more than the solute in high concentration of the solute,
and the Langmir and Freundlich adsorption equations hold only for low
concentrations.

From the isotherms of the three isomers it can be seen that the
delta isomer is adsorbed the most strongly, the gamma isomer next and
the alpha isomer the least strongly. It was surprising to find that
the gamma isomer increased at high equilibrium concentrations to an
adsorption value equal to that of the delta isomer. But it should be
noted that this concentration far surpasses the highest concentration
that could be obtained for delta. The upper limit of each isotherm is
necessarily fixed by the solubility of that isomer. As the solubility
of delta is moh lower than that of gamma it was impossible to extend
the delta isotherm to the higher concentrations. Therefore only the
strength of adsorption at comparable equilibrium concentrations can be
correlated. When this is done the order of adsorption is then as first
stated.

The discussion to this point has pertained only to the adsorption

of pure isomers on alumina with the exception of the gamma isomer which

contained about 5% alpha by weight. It was of interest to see hmw
these pure isomer adsorption isotherms would be effected by having
another isomer present. For’this study a mixture of alpha and delta
isomers was selected. The ratio of delta to alpha ranged from.l:1

to 1.531. As can be seen in Figure 2, the delta isomer still was ad-
sorbed to the greatest extent although it did not reach its maximum
x/m.value until a higher concentration than when by its self. 0n.the
other hand, the alpha isotherm was lowered almost 50% from.its pure
isomer isotherm. This was entirely as expected and even.though simi-
lar experiments using the gamma isomer have not been carried out as
yet, it can be expected that the adsorption.will be lowered just as
alpha was but not to such a large extent. Further it can be expected
that gamma would lower the isotherm.for alpha while alpha would not
have too much effect on the isotherm for gamma.

It was thought that the ratio of isomers in.a mixture would have
an influence on the x/m value but it was found that in the limited
range of ratios used in.the alpha-delta mixture that the ratio had no
effect on this value. However, because the ratios were so limited no
definite conclusions can be drawn. Further work is necessary over a
much wider range before definite conclusions can be reached.

The correlation of this adsorption data with the chromatographic
data of Saur (6) is very good. One might predict from.the adsorption
isotherms that the order of the isomers on the chromatographic column
would be delta in the top zone, gamma in the middle and alpha in the
bottom.zone. Saur found this to be exactly the case when he used an

alumina column to separate the isomers of commercial hexachlorocyclohexane.

His order of elution was alpha first, overlapping slightly with game
which was eluted next. He found it almost impossible to elute the
delta isomer due to its strong adsorption by alumina. If the correla-
tion is correct and taking into consideration the overlapping of gamma
and alpha on elution the isotherm of gamma is too high. As was pre-
viously noted it was believed that the isotherm was high due to conver-
sion of gems to delta. It was found impossible to correct this iso-
therm for the conversion.

The conversion was first noted in the determination of the isotherm
for the gamma isomer. It was noted that the original solution of gamma
contained 95% gamma and 5% alpha. At the maximum there was less than
1% of delta. However in some of the equilibrium solutions as high as
8% of delta would appear. For example in one run the original solu-
tion contained: 0.082 g. of gamma, 0.005 g. of alpha and 0.000 g. of
delta. After 72 hours, in the equilibrium solution was found: 0.034
g. of gamma, 0.002 g. of alpha and 0.009 g. of delta. Here it can be
seen that at least 0.009 g. of the 0.048 g. of gamma that was removed
from solution was due to conversion to delta. Exactly how much gamma
converted to delta is difficult to ascertain as it met be assumed that
some of the delta itself was adsorbed.

The existence of a factor for the conversion of the gamma isomer
to the delta isomer was carefully investigated. Having a factor would
have made it possible to correct the adsorption isotherm of the game.
isomer to true adsorption values. No factor of time of contact with

the alumina or mass of the isomer present was found to exist but a

-14-

slight correlation was found to exist between the amount of conversion
and the amount of alumina that was in contact with isomer. The amount
of conversion increases as the amount of alumina increases. This
correlation proved of little value in correcting the gamma isomer iso-
therm and work along this line was discontinued.

Interpretation of the above data leads to an interesting theory.
If the conversion takes place not only during adsorption by alumina but
also during any adsorption process then the use of hexachlorocyclohexane
as an insecticide would be very limited even if the pure isomer of
gamma was used for this purpose. The reason is that while gamma is
tasteless and. odorless, the delta isomer has a very displeasing odor
and taste which is ever present in vegetation that it has been used on
as an insecticide. It is known that the insecticide is strongly
adsorbed by vegetation. Therefore if conversion takes place even the
pure gamma would give traces of the displeasing delta isomer, making
its use on vegetation that is used for food out of the question.

To be certain that the data being recorded was true adsorption
data, some of the factors were varied. Factors such as the ratio be-
tween weight of solution and weight of adsorbent were varied over a
considerable range. It was found that ratio could be varied over a
considerable range, except when the amount of alumina became too small.
Here it is believed that the adsorption still progresses the same as
with larger amounts of alumina but the amount of isomer that is adsorbed
is so small that slight errors in the analysis would appear very large

in the final x/m value. The lower limit of the amount of alumina that

-15-

could be used was placed at 0.1000 g. Even at this amount it is evident
that any error in the amount of isomer adsorbed is magnified ten times
in the x/m value.

Other factors that were varied are as follows: Some series were
run by varying the concentration of the original solution and holding
the amount of alumina constant. These were followed by a series with
a constant solution and varying the weight of the alumina. To check
the accuracy of the adsorption values found 'for the isomers in the
small amounts that could be used in the 10 m1. ampules, a few series
were run inspecial large glass tubes. Also the method of analysis was
changed on two alpha series. In general the method of analysis was
with the infrared spectrophotometer. In these two alpha series the con-
centrations were determined by accurate weighings. With all of these
variations the values for x/m still were such that they fell on the same
adsorption isotherm. From the above the method can be concluded to be
correct.

The separation of the equilibrium solution from the adsorbent was
made by filtering through ashless filter paper. The possibility that
this procedure would introduce an error in the results due to adsorp-
tion of the isomers by the filter paper or due to loss of solvent by
evaporation during the filtering process was carefully investigated.

A number of solutions of the isomers were filtered under parallel con-
ditions to those encountered in the filtering of the solutions in con-
tact with the alumina. All filtering was carried out in a constant
temperature room that also maintained a constant humidity. The tempera-

ture of the room was 23° 1 0.5° C. and the humidity was 53-55%.

These blank runs determined that if there was adsorption of the isomers
by the filter paper and loss of the solvent due to evaporation that
they balanced each other in such a manner that the concentration of the
solution being filtered remained unchanged during the process. As only
the concentration of the filtrate is necessary in the calculation of
x/m this method of separation was used throughout the work.

Another precaution was the checking of whether alumina contained
any material that would effect the extinction readings of the infra-
red spectrophotometer. Hexane was placed in contact with alumina for
a period of 72 hours and was then analysed with hexane that had not
come in contact with alumina. Both of these samples were evaporated
to dryness and any residue was dissolved in carbon disulphide and ana-
lysed in the spectrophotometer. Both gave the same extinction values
at the wavelengths used for the isomer analysis.

More extensive work was done on the alpha and delta isomers than
on the gamma isomer. There were several reasons for limiting the work
done on the gamma isomer. First, the characteristic wavelength for
gamma analysis by infrared analysis is 14.53 microns. This is a very
low energy wavelength and requires a high amplification to observe the
effects of adsorption. Slight variations in the current make it impos-
sible to obtain steady extinction values. Readings in this range are
therefore subjected to considerable error. As an alternative method of
analysis direct weighing of the isomer was attempted as with the alpha
isomer. Immediately the difficulty of drying the sample arose. Not

only does gamma have a low melting point but as it precipitates from

-17-

hexane it occludes the solvent. At no time was it possible to get con-
stant weights as was possible with the alpha isomer. This method of
analysis was discarded for the gamma isomer. As no satisfactory method
of analysis was obtained for gamma and knowing that conversion of the
gama isomer to the delta isomer was taking place, only enough work
was done on the gamma isomer to obtain a trend of how it was removed

from solution.

-13-

2.

3.

4.

CONCLUSIONS

The order of adsorption by activated alumdna of the three prin-
cipal isomers of hexachlorocyclohexane is; delta the most
strongly adsorbed, gamma next and alpha the least strongly.‘

The order of adsorption by alumina is the same order as observed
on a chromatographic column of alumina. That is, the delta iso-
mer forms the top band on the column, gamma in.the middle and
alpha in the bottom.band.

The gamma isomer is converted in part while in contact with the
alumina, into the delta isomer.

In mixtures of the isomers the most strongly adsorbed isomer is
not influenced too greatly by the other isomers except at low
concentrations. At these low concentrations its isotherm is

lowered but still remains above those of the other isomers present.

-19..

1.

2.

3.

4.

REFERENCE

Dickinson, R. G. and Bilicke, G., J. Am. Chem. Soc., fig, 764 (1928)

Smith, H. P., Noyes, W. A. Jr. and Hart, E. J., J. Am. Chem. Soc.,
§_5_, 4444-59 (1933)

Slade, R. E., Chem. and Ind., _l__9_4_§_, 314-9

Hendricks, S. B. and Bilicke, C., J. Am. Chem. Soc., 48, 3007
(1926)

Gilman, E., Organic Chemistry, An Advanced Treatise, John Wiley
and Sons, New York, 1947, Vol. 1, 2nd Ed., p. 336-7

Saur, R. L., Michigan State College, Ph. D. Thesis (1949)

Daasch, L. 77., Anal. Chem., .1-2' 779-85 (1947)

Lewis, W. K., Squires, L. and Broughton, G., Industrial Chemistry
of Colloidal and Amorphous Materials, Macmillan Co., New York,

1948, p. 90-1

-2 0-

 

 

 

{ T541 222748
J G465 Gilbert

T541 222748
G465 Gilbert
The adsorption of the
alpha, delta and gamma
isomers of hexachlorocyb
clohexane by activated

 

 

 

 

 

 

 

 

 

 

 

 

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