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LD3907 '
•G7 Abrams, A lbert, 1921-
1952 The therm al equilibrium between
•A2 1-2 diiodoethane, iodine, and ethy
lene and the entropy of 1-2 diiodo
ethane.
83p. d ia g rs..ta b le s.
Thesis (Ph.D.) - N.Y.U., Graduate
School, 1952.
Bibliography: p .81-83.
C98311
o
CV,.t» tici
Xerox University Microfilms, Ann Arbor, Michigan 48106
THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED.
UBftART m
m t TORI WIVERFITT
miVESSITT HEIAV-""r
THE THERMAL EQUILIBRIUM BETWEEN 1-2 DIIODOETHANE,
IODINE, AND ETHYLENE AND THE ENTROPY OP 1-2 DIIODOETHANE
ALBERT ABRAMS
A DISSERTATION IN THE DEPARTMENT OF CHEMISTRY SUBMITTED IN
PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY AT NEW YORK UNIVERSITY
ACKNOWLEDGEMENTS
The author wishes to acknowledge his Indebtedness
to Professor Thomas W. Davis for the conception of the
investigation and for his many helpful suggestions dur
ing the course of the work.
In addition, the author expresses his sincere ap
preciation to Professor George M. Murphy and to other
members of the Chemistry Department, and to Professors
Leon H. Fisher and Edward Gerjouy of the Physics Depart
ment for th e ir comments on various phases of the in
vestigation.
- i i
l o <1112
TABLE OF CONTENTS
page
LIST OF TABLES ...................................................................................... iv
LIST OF ILLUSTRATIONS ..................................................................... v
I. INTRODUCTION ............................................................................... 1
II. EXPERIMENTAL ............................................................................... 9
Method ............................................................................... 9
M aterials .......................................................................... 9
Apparatus .............. 12
Safety Measures ............................................................. 16
Procedures ................................................................... 17
Data and R esults .............................................................23
D iscussion ............................................................................34
I II . THEORETICAL.....................................................................................43
General Outline of C alculations ........................ 43
The Molecule ....................................................... • 43
P artitio n F u n ctio n .................................................. 48
T ranslational Entropy ............................................. 49
Internal P artitio n Function ................................ 49
Electronic ........................................... 49
V ib ra tio n ............................................................... 50
R o ta tio n .................................................................. 55
Internal Rotation ............................................ 62
C alculation of Total Entropy ................................ 73
P otential B arrier........................................................... 75
IV. GENERAL DISCUSSION ................................................................. 77
V. SUMMARY........................................................................................... 80
VI. LIST OF REFERENCES ....................................................................81
- iii -
LIST OF TABLES
Table Page
I. V ariation In Counting Rate With Applied
P otential ............................................................................................. 14
II. E ffects of Concentration of Sodium Thio-
sulfate and of Iodine on the Counting Rate
of 1-131 in Aqueous S o lu tio n ................................. 24
I I I . Experimental Results and Equilibrium Con
stants Obtained in Series II and IV .............................. 30
IV. Heat of Decomposition of 1-2 Diiodoethane
from Various Sources
A. Equilibrium Measurements ........................... 37
B. Thermochemical Measurements ............................ 38
V. V ibrational Assignments of the 1-2
Dihaloethanes ................................................... 53
VI. C ontribution of Each V ibration Frequency
to the P artitio n Sum of 1-2 Diiodoethane . . . . . . . 54
V II. Coordinates of the Atoms in Trans 1-2
D iiodoethane..................................................... 57
V III. Coordinates of the Atoms in Skew 1-2
Diiodoethane .................................................................................. 60
IX. Coordinates of the Atoms in the Rotating
Top of Trans 1-2 Diiodoethane ............................................ 68
X. Coordinates of the Atoms in the Rotating
Top of Skew 1-2 Diiodoethane ............................................. 71
XI. In tern al P artitio n Functions of 1-2
D iiodoethane ....................................................... 72
X II. Internal Entropy of 1-2 Diiodoethane at
298.16°K ............................................................................................... 73
X III. Total Entropy of 1-2 Diiodoethane at
298.16°K ............................................................................................... 74
- iv -
LIST OF ILLUSTRATIONS
Figure Page
1. Plot of the Logarithm of Equilibrium
Constants against Reciprocal of the
Absolute Temperature .................................................................. 8
2. System fo r Evacuation, Introduction of
Reactants and P urification of Ethylene ..................11
3. Solution Jacket and Gelger-M ueller Counter .............. 13
4. Counting Rate as a Function of Applied
P o te n tia l .................................................................................15
5. Iodine Tubes and F illin g Apparatus .................................. 18
6. Plot of the Logarithm of Equilibrium
Constants against Reciprocal of the
Absolute Temperature .............................................................. • 35
7. Schematic R epresentation of the R otational
Isomers of 1-2 D iiodoethane................ 56
- v -
I. Introduction
Previous studies of the properties of 1-2 diiodoethane
have included the kinetics of the therm al ° and photochemi
cal^"® decomposition of the compound and the equilibrium ^® *^
between diiodoethane and its decomposition products. A study
has been reported^-® on the combustion of the compound. Wu^®
has interpreted the infra-red and Raman spectra.
The above investigations have established experim entally
th at the products of the decomposition of 1-2 diiodoethane
are iodine and ethylene. Iodine has been id en tified by its
reaction with sodium th io su lfate. Cuthbertson and Kistiakow-
sky-1--1 used a photom etric method to id en tify and analyze the
iodine formed in the decomposition. The presence of ethylene
has been confirmed by its ch aracteristic reaction w ith bro
mine. A recent investigation on the polym erization^ of the
diiodide supports the above conclusion. In addition, Sherman
and Sun^® and Sherman, Quimby and S utherland^ have considered
the problem of the decomposition from a quantum mechanical
view point. They have concluded on the basis of the energetics
of possible reactions th at the decomposition yields iodine
and ethylene.
Slator^ investigated the rate of decomposition of diiodo
ethane in ethyl alcohol and water solution in the presence
of the iodide ion. He® also investigated the effect of th io
su lfate ion on the above decom position. Although the mecha
nism he proposed is unacceptable in lig h t of modem kinetic
theory, S lator did demonstrate th at the addition of the
th io su lfate ion caused a sharp Increase in the ra te of de
composition.
An investigation by Pollisar® on the rate of decomposi
tion in carbon tetrach lo rid e has shown th at the rate could
be interpreted in terms of a unim olecular, iodine catalyzed
decomposition mechanism. The rate of decomposition was ex
pressed by
where ( ) is the concentration of the species and k is the
rate constant.
The rate of form ation of 1-2 diiodoethane was represen
ted by
dt
Although additional Interpretations of the mechanism
have been proposed, the above expressions have been shown to
be essen tially correct over a wide range of concentrations.
On the basis of an experim entally determ ined rate constant
fo r the forward reaction and equilibrium constants, P ollisar
found the heat of reaction for the decomposition to be 11.3
kcals/m ole.
Shumacher has interpreted P o llisa r's data in terms of
a chain mechanism. This rein terp retatio n led to a heat of re
action of 11.5 kcals/m ole at 410° Kelvin. A futher invest! -
- 3 -
gation of the therm al decomposition in solution nas been
reported® .
7—9
Photochemical investigations of the decomposition in
solution have resulted in rates which can be expressed by re
lation s essen tially the same as those proposed by P o llisar
fo r the thermal process. A correction must be made in the
therm al expression, however, to account for the sh ift in the
iodine m olecule-iodine atom equilibrium due to the presence of
lig h t.
g
Arnold and Kistiakowsky have investigated the gaseous
decom position. Their resu lts indicate that the rate constant
is the same in the gaseous phase as in solution. Ogg^-® has
interpreted the resu lts of the above investigation in terms of
a chain mechanism.
A study by Iredale and M artin^ has been reported. A va
lue of 20.0 kcals/m ole for the heat of decomposition has been
calculated by them.
The investigations discussed above have shown th at d i
iodoethane decomposes to yield iodine and ethylene. The rate
of decomposition can be expressed in terms of two processes,
one a unim olecular and the other a chain mechanism, both pro
ceeding with approxim ately the same energy of activ atio n .
The f ir s t thermochemical study of 1-2 diiodoethane was
12
undertaken by Berthe lo t . He determined the heat of combus
tion of the solid diiodide. The end products were gaseous
carbon dioxide, liq u id water and solid iodine. The value,
