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KINETIC STUDIES of SOME THERMAL REARRANGEMENTS Abstract Approved Redacted for Privacy (Major Professor) AN ABSTRACT OF THE THESIS OF Bruce Stewart Schatz for the Ph. D. in Chemistry (Name) (Degree) (Major) 47 ,;,; Date thesis is presented ' r L ` r c. I ; ' L, Title KINETIC STUDIES OF SOME THERMAL REARRANGEMENTS Abstract approved Redacted for Privacy (Major professor) cis -2, cis -4, cis -6- Octatriene (Ia), trans-2, cis -4, cis -6- octatriene (IIa) and trans -2, cis -4, trans -6- octatriene (IIIa) were prepared and subsequently characterized by carbon -hydrogen analyses, ultraviolet spectra, infrared spectra and by nuclear magnetic resonance spectra of both the trienes and their 4, 5- dideuterio analogs. Valence isomerization of IIIa was shown to yield cis -5, 6- dimethyl-1, 3-cyclohexadiene: k = 4. 45 X 10-5 sec-1 at 132', k = 7. 02 X 10-4sec-1 at 165', Ea _ k = 2. 45 X 10-4sec-1 at 152', a 29. 4 kcal /mole and AS _ - 7 e. u. at 149'. Thermal interconversion of Ia and IIa was observed: k = 2 X 10- 5sec -1 at 109. 5' (la -.IIa) and K = 5. 5 (IIa /Ia). Valence isomerization of a mixture of la and IIa yielded trans -5, 6- dimethyl -1, 3- cyclohexadiene: k= 1. 5 X 10- 5sec -1 at 178', k = 6. 4 X 10 -5 sec -1 at 196 °, Ea = 33 kcal /mole and A$$ _ . 9 e. u. at 185' for the disappearance of the mixture. Both cis- and trans -5, 6- dimethyl -1, 3- cyclohexadiene were shown to rearrange to 1, 6-dimethyl-1, 3-cyclohexadiene: k = O. 8 X 10-5sec-1 at 182', k = 3.6 X 10- 5sec -1 at 200', Ea = 36 kcal /mole and LS$: -3 e.u. at 190' for the disappearance of the trans isomer, and k = 1. 85 X 10 5sec -1 at 178', k = 4. 59 X 10- 5sec -1 at 189', Ea = 34 kcal /mole and tS$ _ - 7 e. u. at 183° for the disappearance of the cis isomer. Thermal rearrangement of 1, 6- dimethyl -1, 3- cyclohexadiene yielded o- xylene, p- xylene, ethylbenzene and some unidentified components. Rearrangement of cis -2 -(o- hydroxyphenyl)pent -3 -ene in deu- terium oxide yielded the trans isomer with one deuterium atom in the gamma -olefinic position. Slow incorporation of deuterium was also detected in the alpha- methyl group. The rate of cis to trans isomerization for cis -2 -(o- hydroxyphenyl)pent -3 -ene was shown to equal the rate of olefinic deuterium incorporation. These two studies establish that the abnormal Claisen rearrangement of cis-2-(o-_ hydroxyphenyl)pent-3-ene is a stereospecific reaction. Kinetic studies of the equilibrium of cis- and trans -2 -(o- in water showed Ea = 33 kcal /mole and hydroxyphenyl)pent-3-ene a = - 13 e. u. for trans and Ea = 35 kcal /mole and AS$ = - 12 DS$ cis-. a of 2. 7 at e. u. for trans -.cis. A deuterium isotope effect (kOH /kOD) 205' was calculated from the rates of rearrangement. KINETIC STUDIES OF SOME THERMAL REARRANGEMENTS by BRUCE STEWART SCHATZ A THESIS submitted to OREGON STATE UNIVERSITY in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY June 1967 APPROVED: Redacted for Privacy Professor of Chemistry In Charge of Major Redacted for Privacy Chair an of Department of Chemistry Redacted for Privacy Dean of Graduate School ¡ Date thesis is presented '...,. ( % ¡y Typed by Marion F. Palmateer ACKNOWLEDGMENT The author wishes to express his sincere appreciation to Dr. E. N. Marvell for his helpful guidance and discussion during the course of this work. The understanding and patience of the author's wife, Joann, and son, Michael, have contributed greatly to the successful com- pletion of this study. TABLE OF CONTENTS Page INTRODUCTION 1 HISTORICAL 2 Valence Isomerism of Conjugated Trienes 2 Abnormal Claisen Rearrangement 8 DISCUSSION 16 Valence Isomerism of 2, 4, 6- Octatrienes 16 Introduction 16 Synthesis and Structure Identification 16 Valence Isomerization 21 General Conclusions 30 Abnormal Claisen Rearrangement 35 Introduction 35 Synthesis 36 Degree of Stereospecificity 39 General Conclusions 50 EXPERIMENTAL 52 Valence Isomerism of 2, 4, 6- Octatrienes 52 cis -2, cis -4- Octadien -7 -ol 52 cis -2, cis -4- Octadien -7 -ol tosylate 52 cis -2, cis -4, trans -6- Octatriene and cis -2, cis -4, cis -6- Octatriene 53 4, 5 -d2- cis -2, cis -4- Octadien -7 -ol 54 4, 5 -d -cis -2, cis -4- Octadien -7 -ol tosylate 54 4, 5 -d222- cis -2, cis -4, trans -6- Octatriene and 4, 5 -á -cis -2, cis -4, cis -6- Octatriene 55 1- Pentyn- 3 -ene 56 trans -2- Octen- 4- yn -7 -ol and cis -2- Octen- 4- yn -7 -ol 56 trans -2, cis -4- Octadien -7 -ol and cis -2, cis -4- Octadien-7 -ol 57 trans -2, cis -4- Octadien -7 -ol and cis -2, cis -4- Octadien-7-ol tosylates 58 Page trans -2, cis -4, trans -6 -Octatriene, trans -2, cis -4, cis -6- Octatriene, and cis -2, cis -4, cis -6- Octatriene 58 Separation of 2, 4, 6- Octatriene Mixtures 59 Kinetic Studies 60 Abnormal Claisen Rearrangement 60 2- Hydroxypent- 3 -yne 60 2- Bromopent- 3 -yne 61 2 -(o - Hydroxyphenyl)pent- 3 -yne 61 cis - 2- (o -Hydroxyphenyl)pent- 3- ene 61 trans -2- Bromopent- 3 -ene 62 trans - 2- (p- Hydroxyphenyl)pent- 3 -ene 63 Rearrangement of cis- or trans -2 -(o- hydroxyphenyl)pent -3 -ene in Water or Deuterium Oxide 63 2- (p- Hydroxyphenyl)pent -3 -ene 64 2- Ethyl- 3- methylcoumaran and 3- ethyl- 2- methylcoumaran 64 BIBLIOGRAPHY 8 3 LIST OF TABLES Table Page 1 Synthesis of 2, 4, 6- octatrienes. 18 2 Spectral characterization of Ia, IIa and IIIa. 19 3 Comparison of calculated and experimental con- centrations. 29 4 Comparison of activation parameters. 32 5 Synthesis of cis -2 -(o- hydroxyphenyl)pent -3 -ene (I). 37 6 N. M. R. integrations of trans -phenols. 40 7 N. M. R. integrations of cis -phenols. 40 8 Composition of rearrangement product. 47 9 Rearrangement of cis- and trans -2, cis -4, cis -6- octatriene. 178° 65 10 Rearrangement of cis- and trans -2, cis -4, cis -6- octatriene. 196° 66 11 Rearrangement of trans -5, 6- dimethyl -1, 3-- cyclohexa- diene. 182° 66 12 Rearrangement of trans -5, 6- dimethyl -1, 3- cyclohexa- diene, 200° 67 13 Isomerization of cis - 2-(o-hydroxyphenyl)pent- 3-ene in D20 at 205. 0 + 0. 2°. 68 14 Summary of experimental rates for cis - phenol trans -phenol. 69 15 Rate of olefinic deuterium incorporation of cis -2 -(o- hydroxyphenyl)pent-- 3 -ene at 205. 0 + 0. 2'. 70 16 Isomerization of cis-2,-(o- hydroxyphenyl)pent- 3-ene in hI20 at 204. 7 _ 0. 3', 71 17 Isomerization of cis-2-(o- hydroxyphenyl)pent- 3-ene in H20 at 226. 3 + 0. 3°. 71 LIST OF FIGURES Figure Page 1 Log (triene)t versus time; 0. 66 M (trans- and cis -2, cis -4, cis -6- octatriene) at 178° 72 2 Log(triene)o(triene)t versus time; 0. 66 M (trans- and cis -2, cis -4, cis -6- octatriene) at 196° 73 )o 3 Lo g(diene)t(d. versus time; 0. 66 M trans -5, 6- dimethyl- 1, 3- cyclohexadiene at 182° 74 4 Lo versus time; 0. 66 M -5, 6- )t trans dimethyl- 1, 3- cyclohexadiene at 200° 75 5 N. M. R. of deuterated trans- 2-(o-hydroxyphenyl)pent- 3-ene 76 6 N. M. R. of trans-2-(o-hydroxyphenyl)pent-3-ene 77 C -C 7 Log C -Co0 versus time for isomerizations of cis -2- 0 00 (o- hydroxyphenyl)pent -3 -ene in D2O at 2. 05 ± 0. 2° 78 8 N. M. R. of 2- ethyl -3- methylcoumaran and 3- ethyl- 2-methylcourmaran mixture 79 C 9 Log C versus time for olefinic deuterium incorpora- tion of cis -2 -(o- hydroxyphenyl)pent -3 -ene at 205° 80 C -C 10 Log C C versus time for isomerization of cis-2- 00 (o- hydroxyphenyl)pent -ene in H2O at 205. 0 ± 0. 2° 81 C -C o 11 Log C-C 00versus time for isomerization of cis -2- oo (o-hydroxyphenyl)pent-3-ene in H20 at 226. 3 ± 0. 3° 82 KINETIC STUDIES OF SOME THERMAL REARRANGEMENTS INTRODUCTION Organic reaction mechanisms can be classified into ionic, radical, and molecular processes. Ionic and radical reactions are well known, and methods for studying the mechanisms of these re- actions have long existed. Although molecular reactions have been recognized for some time, many of the ordinary methods for study- ing the mechanisms of other types of reactions have not proved fruit- ful when applied to this class. These molecular reactions are characterized by their (1) sus- ceptibility to thermal induction, (2) inertness to free radical initiators, and inhibitors, (3) insensitivity to acid and base catalysis, (4) in- sensitivity to solvent effects, (5) definite stereochemical require- ments, and (6) first -order kinetics. The work described in this thesis is concerned with expanding the available information on the mechanisms of some molecular re- actions. The kinetic studies herein are devoted to two separate examples of molecular reactions: the valence isomerism of conju- gated trienes, and the abnormal Claisen rearrangement. 2 HISTORICAL Valence Isomerism of Conjugated Trienes The classic example of the valence isomerization between cis trienes and cyclohexadienes is the equilibrium between 1, 3, 5 -cis, cis, cis -cyclooctatriene (I) and bicyclo -[4.2.0] -octa -2, 4 -diene (II) (12). These two isomers readily II interconvert at elevated temperatures, yet they may be isolated in pure form and characterized at room temperature.
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