SPECTROPHOTOMETRIC MEASUREMENTS
OF SQLUTIGNS OF SODEUM METAL
EN ETHYLENEDIAMiNE

T3125 5 {or the Degree of M. 5.
312813;“ STATE UNLE‘EBEETY

Myron Stafford
1963

THESIS

LIBRARY

Michigan State
University

 

ABSTRACT

SPECTROPHOTOMETRIC MEASUREMENTS
OF SOLUTIONS OF SODIUM METAL
IN ETHXLENEDIAMINE

by Myron Stafford

Qualitative Spectra obtained for solutions of sodium
in ethylenediamine indicated the existence of a single
peak at 657 mp4. In order to substantiate the theoreti-
cal explanation of this peak with quantitative experimen-
tal data, and to obtain a value for the molar absorptiv-
ity of such solutions, spectrophotometric measurements
were carried out on solutions of sodium in ethylenediamine.

The Beckman DK-2 spectrOphotometer was used in all
the measurements along with specially constructed appar-
atus for transferring and handling the reactive solutions.
From the first step in the purification of the ethylene-
diamine to the final step before actual measurements were
taken, extreme care was exercised to avoid the admission
of any impurities to any system involved. Out of such pre-
cautions has developed a valuable technique which may be
extended to further work upon other alkali metal—ethylene—
diamine solutions.

The results of the quantitative studies upon sodium—
ethylenediamine solutions indicate that the molar absorp-

4

tivity value lies between 2.5 x 10“ and h.0 x 10 and

l

Myron Stafford

that the oscillator strength is about 0.5. This result
is in accord with the model of Dye and Dewald which pos—
tulates a solvated molecule-ion, Naé, and a de-localized

I"optical" electron.

SPECTROPHOTOMETRIC MEASUREMENTS
OF SOLUTIONS OF SODIUM METAL
IN ETHILENEDIAMINE

By

Myron Stafford

A.THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Chemistry
1963

ACKNOHLEDGEHENTS

The author wishes to express his very deepest gra-
titude to Dr. James.L. Dye for always being so consider-
ate and understanding throughout the author's associa-
tion with him as a student and advisee. It could not
have come at a more appreciated time in the author's
life.

The Atomic Energy Commission is also due recogni-
tion for the source of income supplied while this work
was in progress.

Finally, the author wishes to recognize the sacre-
fices realized by his immediate family during these ed-
ucational years.

And not least of all, the author will always be
able to recall those “friendly comments” and Idestruc-
tive threatsI so eloquently delivered by 'The Boys in
Romm 109' while the writer attempted to teach them an

appreciation for ethylenediamine vapors.

ii

TABLE OF CONTENTS

Page
Introduction........................................ 1
Experimental........................................ 3

I Purification of Ethylenediamine............ 3
II Second Make-up Vessel...................... 5
III Make-up Vessel with Spectral Cell.......... 8
IV Calibration of the Instrument.............. 13

V Procedure for De-gassing the Make-up
Vessel and Cell............................ 13

VI Purification Of metalSOC00......0000000000. lu
VII Cleaning of Glassware...................... 14

VIII Conductivity Measurements of Water
in EthylenediaminBOOOOOOOOOOOOOOOOOOOOOOOOO l6

Results.0...0.0.0....OOOOOOOOOOOOO...00.00.00.000... 18

I Results of Spectrophotometric
Measurements................................ 18

II Results of Conductance Measurements......... 25
III Mass Spectrometer Results................... 26
DiscuSSj-OIIOOOOOOOOOO0.00.0.0....0...‘............... 27

ReferenceSOOOOOOO00.0.00...OOOOOOOOOOOOOO0.0.0.0.... 28

iii

LIST OF TABLES

TABLE Page

1 Data Used to Calculate Molar Absorptivity
valueI...0.0.0....OOOOOOOOCOOOOOOOIO0000...... 18

2 Data Used to Calculate Molar Absorptivity
value IIIOOOOOI0.000.000.0000.OOOOOOOOOOOOOOOO. 19

3 Data Used to Calculate Molar Absorptivity
value IVOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO 21

4 Data Used to Calculate Molar Absorptivity

Value VOOOOOOOOOOOOOOOOOOOOCCIOOOOOOOOOIOOOOOOC 21

5 Data Used to Calculate Molar Absorptivity
value VIOOIIOOOOOOOOOOOOOOOOOOOOOOO.0.0.0.0.... 22

6 Data Used to Calculate the Oscillator Strength. 2h

7 Calculated Oscillator Strengths for Solutions
of Sodium in Ethylenediamine.................. 23

8 Data Obtained from Conductance Measurements of
Solutions of Water in Ethylenediamine.......... 25

iv

 

 

 

   

 

LIST OF FIGURES

FIGURE Page
1 Purification System, Part I................... 6
2 Purification System, Part II.................. 7
3 Diagram of Two-Vessel System.................. 9
u Photographs of Make-up Vessel with Spectral

cellOOOOOOOOOOOI.0.0.0.0.0000...OOOOOOOOOOOOOO ll

LIST OF FIGURES

FIGURE Page
1 Purification syStem, Part I O O O O O O O O O O O I O O O O O O O 6
Purification System, Part II.................. 7

Diagram of Two-Vessel System.................. 9

C'b) N

Photographs of Make-up Vessel with Spectral

C6110...0.0.00...OOOOOOOCOOOOOOOOOOOOOOIOOOOOO ll

INTRODUCTION

Many papers have been authored dealing with the chem-
ical and physical properties of solutions of alkali metals
in liquid ammonia and more recently these studies have
been extended to include the solutions of alkali metals
in amines and ethers. Such an extension is the reason for
this thesis.

The data obtained from the liquid ammonia-alkali me-
tal solutions are in the main presently interpreted on the
basis of two models: the cavity model and the Becker,
Lindquist, and Alder model (1). The name of the former
model epitomizes the theory that supports it; namely, that
in a sodium-ammonia solution, solvated electrons are pre-
sent and the solvated electron is considered to be trapped
in a spherical cavity surrounded by ammonia molecules. In
the B. L. A. model, the two main structural concepts intro-
duced which are different from the cavity model are the ex-
istence of the solvated monomer' LM}(am) / e'(am) = M(amL
and the dimer 4? M(am) : M2(am)J .

However, the data obtained from solutions with amines
and ethers as solvents even qualitatively manifest such
differences that these models alone are not sufficient to
interpret the results. For a discussion of the various
species proposed according to the above models as well as
the proposal of a third and new model which takes into

consideration the new data obtained from solutions of al-

kali metals in amines, the reader is directed to the doc-
toral thesis of R. R. Dewald (2).

In consulting the latter work, it will become evi-
dent that one of the difficult areas in these investiga—
tions using amines concerned the peak obtained at 657 m,a
when absorbance data from the solutions of lithium, so-
dium, potassium, and rubidium in ethylenediamine were ex—
amined. The characteristic most important to the present
work was that among these solutions sodium shows only the
657 peak. This fact plus the desire to determine the na-
ture of the species responsible for this peak logically
indicated that the first quantitative studies be done
using sodium solutions.

The species believed to be responsible for the 657
peak in sodium-ethylenediamine solutions according to the
new model is the solvated diatomic molecule-ion, Naé, with
a delocalized optical electron ”smeared out” over the re-
gion outside the solvated ion. Therefore, it was proposed
that examination of the oscillator strengths obtained from
the spectrophotometric data would indicate whether only
one out of two electrons absorbed radiation and thus whe—
ther the molecule—ion with one non-absorbing and one ”opti-
cal' electron were valid as an explanation for the observed
657 peak. The development of an experimental technique for
Spectral studies would also permit study of the other alka-
li metal-ethylenediamine solutions so that one might explain

these peaks as well.

EXPERIMENTAL

Any and all reliable experimental data obtained from
solutions of alkali metals in ammonia and amines depend
upon the recognition of the great sensitivity of such sol-
utions to the presence of impurities. Therefore, the de-
pendability of any quantitative results obtained from this
work centered around the actual process involved in the
purification of the solvent, ethylenediamine; in the puri-
fication of the sodium metal and all the alkali metals
used in the purification train for the solvent; and in the

handling and cleaning of all glassware involved.

I Purification of Ethylenediamine

To avoid any possible decomposition due to atmospheric
oxidation, the initial three purification steps were carried
out under a constant flow of pre-purified nitrogen while
the final three stages were under vacuum (see diagram of
apparatus in Figures 1 and 2). Reagent grade anhydrous
ethylenediamine of approximately 98% purity was placed in
the first flask which contained BaO and KOH and refluxed
under a constant flow of pre-purified nitrogen for approx-
imately 48 hours. When the heat was first applied to this
system, the ethylenediamine deepened in color from clear
to yellow to a dark brown. Transferral of the liquid to the
second flask which contained sodium wire was accomplished

by discontinuing the water flow through the reflux conden-

1+

ear and allowing the solvent to distil directly into

flask II where it remained for approximately h8—72 hours
under atmospheric pressure of nitrogen. (The ethylene-
diamine may or may not have a blue coloration at this
point. However, if it does, it subsequently fades into a
reddish-brown color with blue streamers radiating out from
the sodium wire proper.)

Since no nitrogen had been allowed to enter flask III
(Figure 2), the next transferral merely involved allowing
the solvent to flow directly from one flask to another
where once again the liquid was refluxed over BaO and KBH
for approximately 48 hours in a stream of pre-purified ni-
trogen.

Through the use of the attached fractionating column
packed with short lengths of 5 mm glass—tubing, the bulk
of the liquid was distilled over at constant temperature
into flask IV; the first fraction being contained in the
SOD-ml waste vessel and discarded. Since flask IV again
contained sodium wire, the solution turned blue immediate-
ly and remained blue for a rather extended period of time.
From this point on all remaining purifications were carried
out under vacuum. After standing over the sodium wire for
several hours, lithium metal was added from the small bent
side-arm or “thumb" by rotating it into an upright posi-
tion. Immediately a deep blue coloration ensued which re-
mained permanently. The solution was allowed to stand for

several hours during which time any hydrogen formed was

pumped off through a cold trap to the vacuum line.

From this point on one must be careful not to over-
heat the ethylenediamine and so produce further decompo-
sition. Therefore, a warm water bath was used to vapor-
ize the liquid to distil it into flask V which was simul-
taneously cooled with an ice-water bath. Since potassium
metal had previously been distilled into flask V through
the use of an attached side-arm which was subsequently

sealed off after the metal distillation, the entire flask

contained a silvery mirror and the blue coloration appeared

immediately when the solvent condensed in the cooled flask.

The blue color remained permanently.

Finally using another warm water bath, the last trans-

ferral was made to flask VI by distilling the liquid over
carefully and slowly avoiding too much heating. Here the

pure colorless liquid was contained and covered with puri—

fied nitrogen so that it could be withdrawn into the second

make-up vessel.

II Secogd Make-up Vessel

The second smaller two—vessel system (Figure 3) was
constructed so that the ethylenediamine would be in con-
tact with sodium metal for the last drying before its use
in the spectrophotometric measurements. This system was
evacuated and heated carefully with a flame to de-gas the
glass surfaces and through the use of the attached side-

arm, sodium metal was distilled into the first vessel

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which would receive the liquid from flask VI and the side-
arm was sealed off under vacuum. The two-way stopcock on
flask VI was then opened allowing approximately 300 ml of
ethylenediamine to flow into the silvery-mirrored vessel
and it immediately turned blue. The stopcock was closed
and re-opened to the high vacuum line through a liquid-
air trap.

Then with the use of a trichloroethylene-dry ice bath,
the blue liquid was frozen and all of the free solvent
droplets were distilled into the cooled portion. This was
followed by removal of the bath allowing the frozen ethylene-
diamine to melt. After several hours, the dry ice bath
was placed on the empty remaining vessel and the ethylene-
diamine was allowed to distil over very slowly. This dis-
tillation was aided by pumping off the hydrogen which was
formed periodically. Also warm air flowing across the first
vessel aided distillation, but care had to be exercised here
so that the blue sodium solution was not carried over direct—
ly through the trap to the clear liquid.

The pure liquid was now stored in this second vessel
and covered with purified helium in preparation for its
transferral to the third set-up of apparatus which held the

cell used in the actual spectrophotometric measurements.

III Make-up_Vessel with Spectral Cell
By examining the photographs in Figure A, one may 10-
cate the following main parts of the complicated-looking

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make-up vessel with its spectral cell: waste vessel (near

cell);

reservoir for pure ethylenediamine; reservoir for

sodium and ethylenediamine solution; measuring cylinder.

With these names and the apparatus actually in hand, the

following eutline of steps may be carried out.

A) Preparation for measurement of the saturated solution

1)

2)

A small amount of ethylenedidmine is poured from the
ethylenediamine reservoir (which is approximately
two—thirds full) into the measuring cylinder.

From the measuring cylinder it is poured (from a
different direction) into the silvery-mirrored re-
servoir. (Sodium metal has previously been dis—
tilled from a side-arm attachment into the sodium-
ethylenediamine solution reservoir and sealed off
under vacuum). In order to obtain a saturated sol-
ution, it is allowed to stand on the metal for ap-
proximately one hour or more. To obtain a uniform
mixture the blue solution is poured back and forth
between the (ethylenediamine-sodium) solution re-
servoir and the measuring cylinder. This opera-
tion is carried out several times. (Avoid allow-
ing the solution to come in contact with the sealed

off area as much as possible).

3) Finally, only a small portion of the saturated solu-

tion is poured into the measuring cylinder, and by
pouring in a different direction, enough solution to

cover the cell is transferred. Then by tilting the

11

Figure 4 PhotOgraphs of Make-up Vessel with Spectral Cefll

 

4)

5)

12

entire apparatus backward so that all the solution may leave
the cell, several rinsings of the cell are made by pouring
the same solution back and forth between the cell and the
"crock" in the cell arm. Finally this solution is poured
into the waste vessel.

Once again one returns to the measuring cylinder and re-
moves a second sample which is large enough in volume to
cover the cell. This may also be rinsed back and forth in
the same manner as above.

The cell is now lowered into the spectrophotometer and po-
sitioned on a V-block especially built for this purpose.
The rest of the apparatus proper is supported on a rod
which is held by a fitting attached to the cover also es-

pecially made for this set-up.

B) Preparation for measurement of a dilute solution

1)
2)

3)

Follow steps one and two in part A above.

A given amount of saturated solution is transferred from
the solution reservoir into the measuring cylinder and
the volume recorded. (Care should be taken to allow all
the solution adhering to the sides of the glass to run
down before making any readings). The measuring cylinder
was calibrated with a 5 cc LueréLok syringe containing
water. The results were: 1 cc of water gave a reading of
1.17; 2 cc of water gave a reading of 0.12; and 6 cc of
water gave a reading of 6.8.

A given amount of clear solvent is transferred from the

solvent reservoir onto the blue saturated solution in the

13

measuring cylinder. This final volume is recorded.

4) The apparatus is now tilted in such a way as if one were
emptying the cell. This should not be done at too sharp
of an angle or loss of material from other reservoirs
will result. Then the solution is poured back again into
the measuring cylinder by tilting it upright. This mix-
ing is done several times until a uniform solution is
obtained.

5) Now enough somution to cover the cell is removed and
the cell is rinsed as directed in number 3-A above.

6) Follow step S-A above.

IV Calibration of the Instrument

All measurements in this work were made on the Model
DK-z spectrophotometer in the near infra-red and visible
ranges. In order to check the accuracy of the instrument,
solutions of neodymium chloride were prepared by dissolv-
ing a definite weight of Nd203 in concentrated HCl in a
5 ml volumetric flask. (The final weight of the Nd203
was taken after it had been heated to 950° C). The molar
absorptivities were calculated using Beer's Law and com-
pared to values for such solutions in the literature.
The results revealed the instrument to be in a proper

working order. (6)

V Procedure for Deegassing the Make-up Vessel and Cell
To de-gas the spectral cell and make-up vessel, it

was suspended on a rack near the high vacuum line, con-

l4

nected to the line, and evacuated. Around this suspended
system, a cylindrical furnace of asbestos paper and alumi-
num foil was built. With the use of a heating element the
temperature of the system was brought to 260-2800 C for

de-gassing and pumped on for 24-36 hours at less than 10-5

torr.

VI Purifigation of Metals

Sodium and potassium were purified by double vacuum
distillation of the best metals available commercially.
The first distillation was made by distilling the metal
into evacuated glass tubes which were sealed off under
vacuum. These tubes were then broken and inserted into
the side-arms provided on the apparatus. The metal was
melted through the constrictions and distilled after
sealing off the melt-down tube.

Lithium metal was out under benzene (through which
argon was bubbled) and quickly transferred to the attach-

ed side-arm which was then evacuated.

VII eani o Glassware

1) Cleaning of the Six—Vessel Distillation System
Many of the parts of this system were annealed in an
oven overnight, but if this were not possible, each
vessel was rinsed first with a dilute solution of HF
cleaner which had the following composition: 2% deter-
gent, ޢ HF, 33% HNOB, and 6Q% water. The RF cleaner

was followed by very thorough multiple rinsings of

2)

3)

15

every part with hot ggpg,;§gig. This was then follow-

ed by very thorough rinsing of every part with distil-
led water, and finally rinsing several times with de—
ionized water.

Cleaning of Two-Vessel System

The entire assembly was cleaned with the HF cleaner
which, after rinsing with water, was followed by thor-
ough cleaning with hot gggg'gggig. The rinsings with
water were the same as given above.

Cleaning of Spectral Cell and Make-up Vessel

Every reservoir and arm of this apparatus was first
rinsed with the dilute HF cleaner being very careful not
to leave the cleaner in the cell for more than a few min-
utes. Next, the main reservoirs and the cell were par-
tially filled with ggpg_;gg;g, and the entire apparatus
was suspended in‘a large glass cylindrical container and
steamed for 24 hours. Then a new solution of ggggIgggig
was added and the steaming procedure repeated. With most
of the ggpg Egggg removed, the apparatus was rinsed with
de-ionized water several times. Then this water was
added to the main reservoirs and cell, and the entire
apparatus again was steamed for 24 hours. This step
likewise was repeated. This was finally followed by sev-
eral rinsings with de-ionized water and the apparatus

dried thoroughly in an oven.

16

VIII Conductivity Measurements of Water in Ethylenediamige

Before the spectrophotometric measurements were carried
out, a set of conductivity measurements were completed on
solutions of water in ethylenediamine. The purpose of
these conductance measurements was to examine the extent
of the following reaction: H20 / en 2 enH/ / OH“ .

l) Conductivity Apparatus

The conductivity apparatus consisted of two main parts.
The first part was made up with the male part of a stan-
dard taper. Extending straight down into this taper was
the capillary and of a calibrated cylindrical vessel which
was connected to the body proper of the calibrated vessel
through a two-way stopcock. The other opening of this
stopcock served to connect the capillary tip with an ordin-
ary cylindrical glass vessel which was separate from the
calibrated vessel and was filled with purified helium.

A small standard taper attached to the very upper side
of the calibrated vessel accommodated an attached side-arm
shaped like a thumb which could hold about 20 ml of water.
By turning this to an upright position water entered the
calibrated vessel. The opposite end of the calibrated ves-
sel (beyond the thumb) was bent in a U-shape and connected
to ordinary glass tubing which at its opposite end was
sealed into the side of the head of the male taper. This
connection was used to equilibrate gas pressure during
transfer.

The second part of the apparatus consisted of an or~

17

dinary Erlenmeyer flask with the female portion of the stan-
dard taper and was equipped at the base with two disk-shaped
platinum electrodes.

2) Experimental Procedure

After evacuating the entire system, the de—ionized water
which had previously been added to the "thumb" was de-gassed
by freezing with liquid air, pumping on the frozen water
through a cold trap connected with the vacuum line, and
then thawing. This was repeated several times.

After transferring about 100 ml of ethylenediamine (the
exact weight of the liquid was obtained by weight differ-
ence) to the Erlenmeyer flask from flask VI of the purifica-
tion train (Figure 2), the entire system was removed from
the vacuum line. The thumb was turned upward and water
entered the calibrated vessel. Purified helium was now re-
leased from the attached cylindrical glass vessel and used
to push each desired amount of water through the capillary
tip into the ethylenediamine. The volume of water added
was read from the calibrated cylindrical vessel.

The conductance cell was now suspended in a constant
temperature oil bath and the resistance of each solution
was measured.

The cell constant was obtained from the measurement of

the resistance of a standardized KCl solution.

RESULTS

I Results of Spectrophotometric Measurements

The data obtained from the spectrophotometric measure-
ments were used first to calculate the molar absorptivity
of the solution. For the shape of the curve, the reader
is referred to the thesis of R. R. Dewald (2).

The first set of data treated involved a solution
which was obtained by the dilution of 1.09 ml of saturated
sodium-ethylenediamine solution with pure solvent to a
final volume of 7.5 ml (0 = 3.49 x 10'“ M).

The data obtained from this solution are listed in Table 1.

Table I Data Used to Calculate Molar Absorptivity Value I

 

 

Peak Number Absorbance,A Time,t(seg) ‘£1t(sec)
First Transfer 1.42 2365 0
1 (Sheet 2) 1.382 2545 180
2 (Sheet 2) 1.212 2645 280
3 (Sheet 2) 1.152 2762 397
4 (Sheet 2) 1.063 2883 518
Second Transfer 1.21 3650 0
1 (Sheet 3) 1.162 3740 90
2 (Sheet 3) 1.192 3880 230
3 (Sheet 3) 1.022 3985 35
(Sheet 3) 0.912 4125 75

Both sets of data in Table l were plotted on semi-log paper
with the absorbance, A, as the ordinate andtit as the ab-
scissa. Extrapolation back to the reapective transfer times
then gave the absorbance values listed flor the solution at
the time of its transferral to the cell.

A molar absorptivity value of 5.2 x 10“

18

liter—cm-l-mole-

l

19

was obtained by plotting the absorbance, A, against time, t
for the two transferral values and extrapolating to zero
time to give an absorbance of 1.82 which represents the ab-
sorbance value of the original solution.

A second set of data was treated in the same manner
for a solution that was prepared by diluting 0.93 ml of the
saturated solution to a final volume of 6.4 ml (0 equals
3.49 x 10'“ M). (This last concentration is the same as the
first concentration for Table 1 only by circumstance).
The data obtained from this solution are given in Table 2.

Table 2 Data Used to Calculate Molar Absorptivity Value II

 

PeakANpmber Absorbance,g. Time,t(seg) £‘3Sse02
First Transfer 1.80 965 0
1 (Sheet 4) 1.770 1190 225
2 (Sheet 4) 1.733 1310 345
3 (Sheet 4) 1.642 1470 505
4 (Sheet 4) 1.580 1665 700
5 (Sheet 4) 1.521 1895 930
6 (Sheet 4) 1.451 2150 1185
7 (Sheet 4) 1.410 2430 1465
8 (Sheet 5) 1.335 2655 1690
9 (Sheet 5) 1.300 2915 1950
10 (Sheet 5) 1.230 3205 2240
11 (Sheet 5) 1.150 3565 2600
12 (Sheet 5) 1.090 3745 2780

20

Table 2 Data Used to Calculate Molar.Absorptivity Value II

 

Peak Number Absorbance,A Time,t(sec) C:t(sec)
Second Transfer 1.70 3925 0
1 (Sheet 6) 1.618 4520 595
2 (Sheet 6) 1.553 4770 345
3 (Sheet 6) 1.534 4890 965
4 (Sheet 6) 1.541 5180 1255
6 (Sheet 6) 1.512 5395 1470
7 (Sheet 6) 1.490 5660 1735
8 (Sheet 6) 1.458 5905 1980
9 (Sheet 7) 1.413 6085 2160
10 (Sheet 7) 1.365 6320 2395
11 (Sheet 7) 1.337 6625 2700
12 (Sheet 7) 1.331 6755 2830
13 (Sheet 7) 1.329 6870 2945
14 (Sheet 7) 1.273 7110 3185
15 (Sheet 7) 1.270 7225 3300

The plot of the two absorbance values for the solution

at the time of transferral and extrapolation to zero time
gave an absorbance value of 1.83. This resulted in a molar
absorptivity of 5.2 x 104 liter—cm'l-mole'l.

A third value for the molar absorptivity was esti-
mated by examining the absorbance of the saturated solu-
tion of sodium in ethylenediamine. The absorbance of this
solution at a wavelength of 493 mixwas 1.542. The value
for A/Amax at this wavelength was found tobe 0.217 (see
Table 6 below). Assuming the shape of the curve to be in-
dependent of concentration yields Amax : 7.1 for the satur-
ated solution. Since the concentration of the saturated
solution is 2.4 x 10'3 M (2), the molar absorptivity is
3.0 x 104 liter-cm-l-mole'l.

After allowing the make-up vessel and cell to stand

21

for more than one week, Dr. Dye made up five more solu-
tions using the sodium that still remained and re-using
the ethylenediamine that was now clear due to decomposi-
tion over this length of time. The first solution was
made by diluting 1.88 ml of saturated solution to a final
volume of 8.5 ml (0 = 5.31 x 10‘“ M). The data obtained
from this solution are given in Table 3.

Table 3 Data Used to Calculate Molar Absorptivity Value IV

 

PeaLNumber Absorbance ,g Time ,tS seg) A t( sag)

First Transfer 1.217 225 0
6 (Sheet 1) 1.139 400 175
7 (Sheet 1) 1.071 570 345
8 (Sheet 1) 1.009 640 415
9 (Sheet 1) 0.468 1530 1305
Second Transfer 1.167 1830 0
10 (Sheet 2) 1.078 1960 130
11 (Sheet 2) 1.053 2115 285
12 (Sheet 2) 0.968 2295 465
13 (Sheet 2) 0.896 2523 693

The molar absorptivity of 2.4 x 104 was obtained after
plotting and extrapolating to zero time the data from
the two transferrals.

The second solution was prepared by diluting 1.24 ml
of the saturated solution to a final volume of 9.6 ml

(0 = 3.10 x 10-4

M). The data obtained from this solution
are given in Table 4.

Table 4 Data Used to Calculate Molar Absorptivity Value V
Peak Number Absorbance,A Time,t(sec) lipgseg)
First Transfer 0.556 240 0

20 (Sheet 4) 0.420 455 215

Table 4 Data Used to Calculate Molar Absorptivity Value V

 

 

 

Peak Number Absorbance.g Time.t(sec) l3t(sec)
21 (Sheet 4) 0.312 640 400
22 (Sheet 4) 0.271 827 587
23 (Sheet 4) 0.222 945 705

Second Transfer 0.275 1120 0
24 (Sheet 5) 0.256 1232 112
25 (Sheet 5) 0.229 1425 305
26 (Sheet 5) 0.200 1602 482

4 1

The molar absorptivity of 2.2 x 10 liter-cm'l-mole' was
obtained from extrapolation of these data.

After diluting 1.40 ml of the saturated solution to
6.0 m1, a third solution of concentration, 5.60 x 10"!+ M,
was prepared. Theéata for this solution are given in
Table 5.

Table 5 Data Used to Calculate Molar Absorptivity Value VI

 

 

Peak Number Absorbanceug TimeLt(seQ) (Btgsec)

First Transfer 1.551 260 0
29 (Sheet 6) 1.489 407 147
30 (Sheet 6) 1.439 530 270
31 (Sheet 6) 1.385 672 412
32 (Sheet 6) 1.360 812 552
33 (Sheet 6) 1.281 1050 790
Second Transfer 1.150 1305 0
34 (Sheet 7) 1.132 1431 126
35 (Sheet 7) 1.104 1553 248
36 (Sheet 7) 1.021 1695 390
37 (Sheet 7) 1.011 2055 750
38 (Sheet 7) 0.924 2820 1515

4 1

A molar absorptivity of 3.0 x 10 liter-cm‘l-mole' was

obtained from extrapolation of these data.

23

The data for the last two molar absorptivities were
obtained at even a later date than those given in Tables
3-5 above. For a solution of concentration 5.97 x 10'1‘L M

which was treated in the same way as those above, a molar

4 -1 -1

absorptivity of 3.3 x 10 liter-cm -mole was obtained.

For the last solution of concentration 4.63 x 10-4 M, the

4 -1

value for the molar absorptivity was 3.1 x 10 liter-cm

mole’l.
In order to aid in the interpretation of these re-
sults, the oscillator strength was next calculated using

the following data and the equation (3)

 

r1 : 4.319 x 10'9[' 9 n0 Elai d ;
-(n2 / 2)23
or f1 - (4. 319 x 10-9) (0.773) amax ) A/Amax d‘:

where no : 1.454 (4).
The integral in this equation was evaluated by plotting

A/A against wave number and finding the area under

max
the curve. The values used for this curve are given in
Table 6. The area was found to be 5311 cm-1. Using
this area and the value obtained from the refractive
index substitution, the data in Table 7 were obtained.

Table 7 Calculated Oscillator Strengths for Solutions of
Sodium in Ethylenediamine

 

 

Oscillator
Molar Absorptivity, amax SSSESggation Strepgths
5.2 x 10: 3. 49 x 10:: 0.926
5.2 x 10“ 3. 49 x 0&3 0.926
3.0 x 10 2.4 x 10.“ 0.525
2.4 x 104 5.31 x 10 0.426

24

Table 6 Data Used to Calculate the Oscillator Strength
A/Amax Wavelength (m1) Wavenumber (x 10'2) (cm-1)

0.103 820 122.0
0.139 812 123.2
0.175 800 125.0
0.211 794 125.9
0.247 787 127.1
0.284 781 128.0
0.320 775 129.0
0.392 764 130.9
0.428 761 131.4
0.465 758 131.9
0.501 752 133.0
0.537 748 132.7
0.609 735 136.0
0.645 732 136.6
0.682 725 137.9
0.718 719 139.1
0.790 716 139.7
0.826 710 140.8
0.863 703 142.2
0.899 695 143.9
0.935 687 145.6
0.971 679 147.3
1.000 657 152.2
0.971 640 156.2
0.935 635 157.5
0.899 629 159.0
0.863 623 160.5
0.826 619 161.6
0.790 615 162.6
0.754 610 164.0
0.718 608 164.5
0.682 603 165.8
0.645 597 167.5
0.609 594 168.3
0.573 592 168.9
0.537 587 170.4
0.501 584 171.2
0.465 580 172.4
0.428 572 174.8
0.356 557 179.5
0.320 550 181.8
0.284 535 187.0
0.247 515 194.2
0.211 482 207.5

25

Table 7 Calculated Oscillator Strengths for Solutions of
Sodium in Ethylenediamine (continued)

 

Solution Oscillator
Molar Absorptivity,amax Concentration Strengths
2.2 x lot 3.10 x lojfi 0.390
3.0 x 104 5.60 x 10_4 0.525
3.3 x 101+ 5.97 x 10-4 0.585
3.1 x 10 4.63 x 10 0.550

If the species present is the Naé . e‘ dimer as pos—
tulated by Dye and Dewald, then only one electron would
absorb to give the 657 peak in sodium-ethylenediamine sol-
utions. An oscillator strength greater than 0.5 would not
be expected. However, if for some reason, one mole of
electron for each mole of sodium is involved in the absorb-

ance, an oscillator strength near unity would be expected.

II Results of Condugtance Measurements

Using the value for the cell constant of 0.2496 cm'l,

the data in Table 8 were obtained from the measured resis-
tances of each solution (water in ethylenediamine).

Table 8 Data Obtained from Conductance Measurements of
Solutions of Water in Ethylenediamine

Concentration of H20(M) ngdugtance,L(cm'lohmIE) A];

 

0 0.753 x 10:2 0 _6
0.139 0.796 x 10 6 0.043 x 10
0.390 0.858 x 10:6 0.105 x 10"6
0.878 m.016 x 10 0.263 x 10'

Using the values from Table 8, AL x 106 was plotted against
the concentration of water in ethylenediamine. Extrapola-
tion to a l M solution concentration gavd an approximate

value of 0.28 x 10"6 cm'lohm-l for c;L.

26

To determine the extent of the reaction,
H20 / en : enH’z / OH"
the equilibrium constant for the reaction was calculated.
Using an approximate value of 50 for the equivalent con-
ductance of each ion in the reaction, the concentration
could be obtained for each ion since,

“2.: 1000uL “:50
°i
Since the weight of the ethylenediamine used was 97.3 grams
(c = 15 M) and the concentration of the water was 1 M, the
equilibrium constant is approximately 2 x 10'12. This

value indicates that water does not react with ethylene-

diamine to any appreciable extent.

111 Mass Spectrometer Results: Nitrogeg
After allowing the ethylenediamine to stand in the

presence of the sodium metal for approximately three

weeks under an atmosphere of helium, a test portion of the
gas was collected and analyzed with the use of the mass
spectrometer. The results showed peaks due to break down
products of ethylenediamine as well as peaks which show-

ed that there was 8.8% hydrogen and 0.6% nitrogen.

DISCUSSION

One of the main purposes of this work was to estab-
lish as closely as possible a value for the molar absorp-
tivity of solutions of sodium in ethylenediamine. Direct-
ly related to this problem was an experimental test of
the plausibility of the proposal that the species present
which is reSponsible for the 657 peak obtained with sodium-
ethylenediamine solutions is the ionic-covalent dimer,

Naé . e' . Examination of the data listed in Table 7 re-
veals that the oscillator strength is probably closer to
0.5 rather than to unity. This would indicate that the
species present could be the solvated molecule-ion with
its 'optical' electron so that only one out of the two
electrons absorbs. The molar absorptivity for the sodium—
ethylenediamine solution appears to lie between 2.5 x 104

1+ l‘mOle-le

and 4.0 x 10 liter-cm-

It is well to indicate here that the two highest
values of the molar absorptivity and oscillator strengths
could be in error since they were obtained in the first
runs and it was discovered later that much of the satur-
ated solution adhered to the glass and ran into the volu—
metric vessel only slowly. This.would result in a high
value for the concentration of the solutions.

The data obtained from the analysis of the gas over
the sodium-ethylenediamine solutions with the mass spec—
trometer indicates that the data reported by Windwer and
Sundheim (5) to the effect that nitrogen and hydrogen are

formed in a ratio of 2:1 may be incorrect.

2?

REF SR ENC 3.13
1. E. Becker, R. Lindquist and B. Alder, 1, gagg, Phys,,

2. R. Dewald, Ph. D. Dissertation, Michigan State
University (1963).

3. L. Pauling and E. Wilson, “Introduction to Quantum
Mechanics,‘ McCraw-Hill Book Company, Inc..
New York, N. Y.

4. "Handbook of Chemistry and Physics," Chemical Rubber
Publishing 00., Cleveland, Ohio (40th Edition).

5. S. Windwer and B. Sundheim, g‘_§hy§g_gp§m‘, 55.
1254 (1962).

6. D. S; tewart and D. Kato, Analytical Chemistry,
01 1958).

28

Mummy LinARY

 

 

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