MECHANISM OF THE CHROMIC ACID OXIDATION OF ALCOHOLS by DONALD GARRY LEE BA ...

239 Pages·2010·8.7 MB·English

MECHANISM OF THE CHROMIC ACID
OXIDATION OF ALCOHOLS
by
DONALD GARRY LEE
B.A., University of Saskatchewan, 195#
M.A., University of Saskatchewan, I960
A THESIS SUBMITTED IN PARTIAL FULFILMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
in the Department
of
CHEMISTRY
We accept this thesis as conforming to the
required standard
THE UNIVERSITY OF BRITISH. COLUMBIA
March, 1963
In presenting this thesis in partial fulfilment of
the requirements for an advanced degree at the University of
British Columbia, I agree that the Library shall make it freely
available for reference and study. I further agr.ee that per
mission for extensive copying of this thesis for scholarly
purposes may be granted by the -Head of my Department or by
his representatives» It is understood that copying.'or publi
cation of this thesis for financial gain shall not be allowed
without my written permission.
Department of C^^^^yyvNui^^^Tc^
The University of British Columbia,.
Vancouver 8, Canada.
Date 1y^&-i£ 1 / & 3
The University of British Columbia
FACULTY OF GRADUATE STUDIES
PROGRAMME OF THE
" FINAL ORAL EXAMINATION
FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
of
DONALD GARRY LEE
PUBLICATIONS B.A. , The University of Saskatchewan, 1958
M.A. , The University of Saskatchewan, 1960
Rearrangement Studies with C^4, X. Ethanol-
2-C14 from the Irradiation of ethanol-1-C14 MONDAY. APRIL ,29th^ 1963, AT 9s30 A.M.
with Co60 Gamma Rays. Can. J. Chem. 38. 2 3 15
IN ROOM 261, CHEMISTRY BUILDING
(1960) C.C. Lee and D.G. Lee
2-Phenylethyl-Iodide from the Irradiation
COMMITTEE IN CHARGE
of 2-Phenylethyl-l-C14 Iodide with Cobalt-60
Gamma Rays. Radiation Research 17, 536 (1962)
Chairman: F.H. Soward
C.C.. Lee, D.G. Lee, and I.S. Bhardwaj
W.A. Bryce R.E. Pincock
Rearrangement Studies with C14, XIII. The
W.R. Cullen R. Stewart
Thermal Decomposition of l-C^4-2-Butyl Chloro-
C.A. McDowell D.S. Scott
sulphite. Tetrahedron 18, 1395 (1962) C.C. Lee
J.W. Clayton, D.G. Lee and A.J. Finlayson
External ExaminerF.H. Westheimer
Harvard University
MECHANISM OF THE CHROMIC ACID
OXIDATION OF ALCOHOLS A spectroscopic investigation of the variation of
the pKa of chromic acid with changes in the identity
of the mineral acid solvents was made, and the re-
ABSTRACT suits were applied to explain observed variations in
the rate of oxidation of isopropyl alcohol in solu
The relative rates of chromic acid oxidation of tions of' different mineral acids a ll having the same
eight aryltrifluoromethylcarbinols were determined acidity.
in 77.27o acetic acid medium. The primary deuterium
isotope effects of these alcohols ranged from 7.40 The results are best explained in terms of a uni-
for jD-tolyltri fluoromethylcarbinol to 12.93 for 3.5 molecular decomposition of a chromate ester via a
;
dinitrophenyltrifluoromethylcarbinol at 25° . The cyclic transition state.
rates fitted a Hammett plot best when modified <T +
substituent values were used and a modified "rho"
value of -1.01 was observed.
The rates of oxidation of several halogenated-2-
propanols as well as their corresponding 2-d ana
logues were also determined in 77.27, acetic acid and
GRADUATE STUDIES
in 50.17, sulfuric acid. Results indicated that whil
the isotope effect varied with changes in the nature
of the alcohol being oxidized, it was constant for a
particular alcohol in solutions of varying acidity.
Field of Study: Physical Organic Chemistry
The thermodynamic parameters for the oxidation of Topics in Physical Chemistry R.F. Snider-
two different alcohols under a variety of conditions
J.A.R. Coope
were determined and found to be approximately the Topics in Organic Chemistry R„A. Bonnett
same, A H# = 9 kcal/mole, AS# = -40 cal/mole deg.
R, Stewart
J. Kutney
An extensive investigation of the oxidation of Physical Organic Chemistry R. Stewart
alcohols in sulfuric acid solutions ranging from 5
R.E„ Pincock
to 957o was conducted and a spectroscopic study was
Inorganic Reaction Mechanisms J. Halpern
made of the behaviour of chromium VI in this entire
Organic Reaction Mechanisms R.E, Pincock
region.
A Q-* value was obtained for the CF3 group and
this was used to determine the "true rate constant",
Related Studies:
k = k bs/K> f°r the chromic acid oxidation of a
0
series of primary alcohols,, A Taft (j* - p* plot
Differential Equations S.A. Jennings
then yielded a p* value of -0,92 for the rate de
Light J.J. Veit
termining step of this reaction.
(ii)
ABSTRACT
The relative rates of chromic acid oxidation of
eight aryltrifluoromethylcarbinols were determined
in 77.2$ acetic acid medium. The primary deuterium
isotope effects for these alcohols ranged "from 7.40
for £-tolyltrifluoromethylcarbinol to 12.93 for 3,5-
dinitrophenyltrifluoromethylcarbinol at 25°. The
rates fitted a Hammett plot best when modified <5N+
substituent values were used and a modified wrhott
value of -1.01 was observed.
The rates of oxidation of several halogenated-
2-propanols as well as their corresponding 2-d
analogttas were also determined in 77.2$ acetic acid
and in 50.1$ sulfuric acid. Results indicated that
while the' isotope effect varied with changes in the
nature of the alcohol being oxidized, it was constant
for a particular alcohol in solutions of varying
acidity.
The thermodynamic parameters for the oxidation
of two different alcohols under a variety of conditions
were determined and found to be approximately the same,
= 9 kcal/mole, = -40 cal/mole deg.
An extensive investigation of the oxidation of
alcohols in sulfuric acid solutions ranging from 5 to
95$ was conducted and a spectroscopic study was made
(iii)
of the behavior of chromium VI in this entire region,,
A <5~* value was obtained for the CF^ group and
this was used to determine the "true rate constant",
k = k /K, for the chromic acid oxidation of a
QlD5
•if- $
series of primary alcohols. A Taft - 6 plot
then yielded a £ value of -0.92 for the rate
determining step of this reaction.
A spectroscopic investigation of the variation
of the pKa of chromic acid with changes in the identity
of the mineral acid solvents was made, and the results
were applied to explain observed variations in the
rate of oxidation of isopropyl alcohol in solutions of
different mineral acids a ll having the same acidity.
The H acidity function for nitric and phosphoricN
Q
acid systems with a 1:1 molar ratio of sodium
perchlorate was also determined.
ACKNOWLEDGMENTS
The author wishes to express his sincere
appreciation to Dr. Ross Stewart for his
guidance during the course of this research
and for his constructive criticism during
the preparation of this thesis.
Grateful acknowledgment is also made to
the University of British Columbia for the
award of two Teaching Assistantships (1960-61
and 1961-62), and to the National Research
Council of Canada for the award of a Student
ship (1961-62).
(v)
TABLE OF CONTENTS
Page
I. HISTORICAL INTRODUCTION
1. Chromic Acid^Oxidation of Organic Compounds 1
2. Chromic'Acid Oxidation of Alcohols 3
3. Primary Kinetic Isotope Effects 24
II. SCOPE OF THE PRESENT INVESTIGATION 36
III. EXPERIMENTAL 39
1. Materials
(i) Alcohols 39
(ii) Inorganic Reagents 53
(iii) Indicators 54
2. Kinetic Methods 55
(i) Iodometric Method 56
(ii) Spectrophotometric Method 64
3. Consideration of the Acid Chromate-
Bichromate Equilibrium 64
4. Product Analysis 65
5. Determination of pKa Values for HgCrO^ 67
6. Acidity Function for the Phosphoric Acid-
Sodium Perchlorate System 72
7. Acidity Function for the Nitric Acid-
Sodium Perchlorate System 79
Determination of the Chromate Ester
Equilibrium Constant for 2-Methoxy-
1 ethanol and 2,2,2-Trifluoroethanol 80
(vi)
Page
IV. RESULTS AND DISCUSSION
1. Oxidation of Fluoro Alcohols in 77.2$
Acetic Acid 85
2. Oxidation of some Halogenated 2-propanols
in 50.1% Sulfuric Acid 101
i
3. Variation in the Magnitude of Isotope
107
Effects with Changes in Acidity
109
4» Thermodynamic Parameters
5. Oxidation in Concentrated Sulfuric Acid 113
Solutions
6. Determination of the 6 Value for the
136
CF^ Group
7. Determination of the "True Rate Constant",
k2 = kobs/K* f or t he C h r o m ic Acid
Oxidation of some Primary Alcohols 138
8. Acidity Functions for Nitric and Phosphoric
Acid Solutions with Added Sodium
Perchlorate 143
9. Variation in the pKa of Chromic Acid with
Changes in the Identity of the Mineral
Acid Solvent 149
10. Variation in Rate of Chromic Acid Oxidations
with Changes in the Identity of the
Mineral Acid Solvent 166
V. CONCLUSION 175
VI„ SUGGESTIONS FOR FURTHER RESEARCH 181
VII. APPENDIX 133
VIII. BIBLIOGRAPHY 134
(vii)
TABLES
I. Variation in Theoretical Isotope Effects 28
with Temperature
Hi Data for Rate Plots 59
III. Acidity of Solutions Containing a 1:1 Molar
Ratio of H .P0 to NaClO^ 74
3 4
IV. Acidity of Solutions Containing a 1:1 Molar
Ratio of HNO^ to NaClO^ 75
V. Data for Figure 10 84
VI. Oxidation of Fluoro alcohols, in 77.2% Acetic
Acid 86
VII. Variation in Rate of Oxidation of
Phenyltrifluoromethylcarbinols in 77.2$
Acetic with H 101
Q
VIII. Rates of Oxidation of Substituted 2-Propanols
in 50.1$ Sulfuric Acid 104
IX. Deuterium Isotope Effects for the Oxidation
of Isopropyl Alcohol in Perchloric Acid
Solutions of,Varying Acidities 108
X. Heats and Entropies of Activation for the
Oxidation of Substituted 2-Propanols
Under Various Conditions 110
XI. Rates Used in Calculation of Thermodynamic
Parameters 111
XII. Extinction Coefficients of Chromium VI in
Sulfuric Acid Solutions 117
XIII. Oxidation of CF^CROHCH^ by Chromium VI in
Sulfuric Acid Solutions at 25.0°C. 123
XIV. Oxidation of CH CROHCH in Sulfuric Acid
3 3
Solutions 124
XV. Oxidation of 1,1,1,3,3,3-hexafluoro-2-
propanol in Sulfuric Acid Solutions 125