Table Of ContentThe Pennsylvania State College
The Graduate School
Department of Chemistry
POLAROGRAPHIC BEHAVIOR OF HALOGENATED
ACIDS AND ESTERS
A dissertation
Chlng-siang Tang
Submitted in partial fulfillment
of the requirements
for the degree of
Doctor of Philosophy
August 1951
i
Approvedi
ax^ Z,!?*-!
Thesis Supervisor
ftUG.-2-JgS]
Head of the Department
li
TAB IE OF CONTENTS
East.
PART I
Effect of Ionic Strength, Buffer Nature and Concentration, and pH*
Introduction 1
Experimental A
Materials A
Apparatus 5
Preparation of Buffer Solutions 5
Procedure 6
Calculation of Ionic Strength 7
Discussion 7
Effect of Ionic Strength 8
Effect of Buffer Component Concentration 9
Effect of pH 11
Behavior in Non-buffered solution 11
Conclusion 11
Table I 13
Table II U
Figure I 15
Figure II 16
PART II
Analysis of Mixtures of Dichloroacetic and Trichloroacetic Adds*
Introduction 17
Experimental Work 17
Materials 17
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Zmsl
Apparatus 18
Basis far Procedure 18
Calibration Procedure 19
Analytical Procedure 19
Data 20
Discussion 21
Summary 22
Table III 24
Table IV 25
Table V 26
PART III
The Chloroacatic Acids and their Raters
Introduction 27
Experimental 28
Materials 28
Buffer Solution 29
Apparatus 29
Procedure 29
Calculation of Ionic Strength 30
Results and Discussion 30
Monochloroacetic acid 30
Dichloroacetio Acid 30
Trichloroacetic Acid 31
(1) Effect of pH 32
(2) Effect of Buffer Component Concentration 32
(3) Effeot of Ionic Strength 32
(A) Effect of Temperature 33
iv
P m
Acids and Esters in Non-buffered Solution 35
Ethyl Monochioroacetate 36
Ethyl Dichloroacetate 37
Ethyl Trichloroacetate 37
Diffusion Current Constants of Three Esters 38
Values of a of the Three Esters 38
Relative Effect of the Functional Groups 39
Conclusion AO
Table VI 42
Table VII 43
Table VIII-A 44
Table VIII-B 45
Table VIII-C 46
Table VIII-D 47
Table IX 48
Table X 49
Table XI 50
Table XII 51
Figure III 52
Figure IV 53
Figure V 54
PART IV
The Ethyl Esters of the Broaoacetic Adds
Introduction 55
Experimental 55
Results and Conclusions 55
Table XIII
Bibliography
Acm»LgmKMBHT
The author wishes to express her sincere
appreciation to Dr. Philip J. Siring for
his guidance and encouragement throughout
this inrestigation. The author wishes to
thank the Research Corporation and the
Atomic Energy Commission for grants-in-aid
which supported this research project.
EFFECT OF IONIC STRENGTH, BUFFER NATURE
AND CONCENTRATION, AND pH
INTRQDUCTIQN
Although the importance of the effect of pH on the polarographic
reducibility of organic oonpounds has been deaonstrated in recent years,
there has been no systematic study of the effect of ionic strength and its
variation due to the use of various buffers in the polarographic investi
gation of organic compounds.
The usual practice in buffering solutions for organic polaro
graphic study is to use a standard buffer or set of buffers at the con
centrations listed in the literature, e.g., the handbooks. However, any
one buffer, even if used over a pH range of only two units, can vary
tremendously in ionic strength. For example, in the case of a phosphate
or citrate buffer used in the region of pH equal to the pKa of the third
ionisation, the ionic strength can change by a factor of 9/4 over the
recomended pH interval of 2 (pKa 11). Such changes in ionic strength
with one buffer over a pH range or between two buffers at any one pH are
probably responsible for much of the confusion arising when attempts are
made to duplicate reported values. In addition, even if two different
buffers at the same ionic strength are used, polarographic results say vary
considerably depending on the nature of the buffer components. These varia
tions can lead to distortion that will completely mask the pH-dependanee of
the process. It is this type of confusion that has led to the attempt made
in this study evaluating the phenomena of variation of polarographic
behavior with ionic strength and buffer composition.
One of the earliest observations of the effect of specific buffer
components on the half-wave potential, Eq.5» was wade by Furman and Stone^
in the course of the investigation of the polarographic behavior of several
anthraquinones in various commonly used buffering media; shifting of the
£q'2 to more negative values was taken as evidence of complex formation
with borate and phosphate buffers. On further investigation, Stone** found
that buffer constituents may play a vital role in the polarographic re-
duction if a relatively stable species is formed between the buffer anion
and the reducible material or one of its reduction products. DeFord and
Andersen^ have studied the variation of the Eq^ of cadmium as a function
of ionic strength in various supporting electrolytes of ionic strengths
extending up to 12 M; Eq^ at first became more negative as the ionic
strength increased and then shifted to less negative values with continued
increase of ionic strength, the magnitude of the shift depending on the
nature and total ionic strength of the supporting electrolyte. Elving,
Rosenthal, and Kramer^ investigating iodoacetic acid and the bromoacetic
acids, found that in some cases where two or more buffers at the same pH
and ionic strength were used, significant variations in the Eq.5 were
obtained. The variation of the buffer component concentration has been
1 3 L 7
found to effect the En _of reducible organic compounds •
Since such phenomena are of great importance to the interpreta
tion of the data obtained in the polarography of organic compounds, a study
has been made of the polarographic behavior of alpha-bromp-n-butvrie acid
over the pH range of 1*0 to 12.4 and the normal working range (0.1 to 3 M)
of ionic strength, using most of the commonly encountered buffer systems.
3
Ionic strength was varied in two ways, (l) by altering the buffer component
concentration and (2) by the addition of potassium chloride* The concen
tration of the buffer components was varied in order to determine the magni
tude of this effect on the Bq#^j it was hoped that soan indication would be
obtained as to whether interaction between the electroreduoible substance
and the buffer components occurred* Any variation of Ho* 5 under identical
conditions including similar ionic strength, except that of buffer component
concentration, could be interpreted as being due to the formation of complex
species* It was felt that from the data obtained in this study, the optimum
operating conditions for each buffer could be determined and some insight
be gained into the nature of the reduction process and the factors in
fluencing it*
The selection of alpha-bromo-fHmtyric acid as the substance to
be used in this investigation was based on several factors* The Hq#5 is
within the readily measurable range of -0*3 to -1*4 volts far the pH range
of 1 to 131 this potential range permits the use of all of the comum
buffers, some of which give decomposition waves beginning at relatively
low potentials* The compound itself is stable over the tine required*
In addition, the compound, containing a four-carbon chain, is not the intro
ductory member of the series* It was felt that it was best to avoid the
introductory members of series since they usually behave in an anoaulous
manner*
The reduction of the alpha-bromo-o-butyrlc acid involves the
fission of the carbon-bromine bond and the formation of g-butyrio acid*
The electrode reaction is irreversible as indicated by the slope of the
wave; the Ukovic equation indicates the two-electron reduction prooess
which results in current flow* The latter is a diffusion-controlled prooess
as indicated by the effects of variation of concentration of reducible
species, of head of mercury and of teaperature variation open the current
flow. While not of absolutely symmetrical character as is the wave ob
tained in the case of a reversible species, the wave is sufficiently well-
defined so that there can be little question as to the determination of
the polarographic values fron it*
It snst be borne in mind that while this particular conqpound
yields the behavior reported, it does not necessarily follow that all
other reducible organic species will show the sane type of behavior*
However, the results reported indicate a behavior which nay be found with
other substances* In particular, similar effects have been observed in
the polarography of other halogenated compounds where the electrode re
action involves the fission of carbon-halogen bonds* Studies similar to
the one described should be made of other irreversible organio systems as
well as of reversible organic systems* It would be of considerable interest
to investigate irreversible and reversible redox systems in which ionisap-
tion does not ocour in order to determine whether the sigmoid curve and
iao-Kyu point phenomena subsequently discussed are associated with pH-
dependence*
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MATERIAIS. All buffer components were analytical reagent grade
chemicals* The alpha-bromo-ft-butyric acid (Kastman Kodak white label) was
recrystallised several times from pentane. The values of the melting point
and the density agreed with those reported in the literature* The compound
was polarographically pure* As solutions of alpha-bromo-ffc-butyrlc acid
stood, slow decomposition of the acid occurred, e*g*, a decrease of 25% in
the diffusion current of 0*$ mg alpha-braeo-p-butyric acid in Buffer C at
