A PROPOSED RADICAL- CHAIN PATHWAY FOR PHOTOINITIATED REDUCTIVE- DEHALOGENATION AND SUBSTITUTION REACTIONS OF HETARYL AND ARYL HALIDES IN METHANOLIC METHOXIDE By GEORGE ALLISON LOCKO A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIPJIMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1976 UNIVERSITY OF FLORIDA 3 1262 08552 5797 To Mom and Dad ACKNOWLEDGEMENTS The author wishes to express sincere gratitude to Dr. John A. Zoltewicz, Chairman of his Supervisory Committee, for his guidance during the course of the research which is reported herein. Without the keen insight of Dr. Zoltewicz much of this work would not have been possible. Apprecia- tion is also expressed toward the other members of his committee: Dr. William R. Dolbier, Dr. Paul Tarrant, Dr. Kuang-Pang Li, and Dr. Charles Allen, Jr. The author is very grateful to Ms. Ann Kennedy for the long hours which she spent typing the manuscript. Very special thanks are extended to Sara for her love, patience, and understanding. Ill TABLE OF CONTENTS Page ACKNOWLEDGEMENTS iii LIST OF TABLES vii LIST OF FIGURES xiii ABSTRACT xvi CHAPTER: I. INTRODUCTION MECHANISTIC INVESTIGATIONS INVOLVING THE PHOTOINITIATED RADICAL-CHAIN RE- DUCTIVE- DEHALOGENATION AND PHOTOINITI- ATED SRi^jl REACTION OF 3-IODOPYRIDINE WITH THIOPHENOXIDE ION IC Results 10 Discussion 58 STRUCTURE-REACTIVITY CORRELATIONS AND RELATED INVESTIGATIONS PERTAINING TO THE PHOTOINITIATED REACTIONS OF HETARYL AND ARYL HALIDES WITH THIOPHENOXIDE ION IN METHANOL 89 Results 89 Discussion 144 INVESTIGATION INTO THE MECHANICS BY WHICH PHENYL SULFIDE AND lODOBENZENE ARE CONVERTED TO BIPHENYL DURING IRRA- DIATION IN METHAlNlOLIC METHOXIDE 182 Results 182 Discussion 200 IV Page EXPERIMENTAL 217 Instrumentation 217 Chemicals 218 Preparations 221 Photolysis Procedures 226 Preparation of Solutions for Photolysis 227 Preparation of Solutions for AIBN and PAT Initiated Experiments 227 Sample Degassing Procedures 228 Column Preparation and Routine Oper- ating Procedures for Gas-Liquid Chromatography 228 Cut and Weigh Method of Integration for Gas-Liquid Chromatography 230 Molar Response Factors for Gas-Liquid Chromatography 2 31 Quantitation of 3-Iodopyridine , Pyridine, and 3-Phenylthiopyridine by Gas- Liquid Chromatography 239 AIBN Controls for Gas-Liquid Chromato- graphy 253 Control Experiments Undertaken to Deter- mine Whether the Internal Glc Standard, Anisole, is Consumed During Sample Irradiation 255 Products Derived from Thermal Decomposi- tion of PAT in Methanolic Methoxide 256 Product Confirmation by GC-MS Analysis 257 Low Voltage GC-MS Analysis of Labeled Biphenyls 260 Kinetic Study of the Reaction of 2-Bromo- thiazole with Sodium Methoxide 260 Page Photolysis of N- tert-Butyl-a- Phenyl- nitrone and 2-Methyl-2-Nitsosopro- pane in Methanolic Methoxide Con- taining Thiophenoxide Ion 267 VI LIST OF TABLES Table Page 1 Effect of Methoxide Ion Concentra- tion of the Rate and Extent of the Photoinitiated Reductive-Dehalogen- ation of 0.31 M 3-Iodopyridine in Methanol n 2 Effect of Degassing on the Extent of the Photoinitiated Reductive-Dehal- ogenation of 0.31 M 3-Iodopyridine in 0.43 M Methanolic Methoxide 15 3 Effect of Degassing on the Extent of the Photoinitiated Reductive-Dehal- ogention of 1.4 x 10~2 m 3-Iodopyri- dine in 0.31 M Methanolic Methoxide 17 4 Attempted Inhibition of the Photo- initiated Reductive-Dehalogenation of 1.4 x 10~2 M 3-Iodopyridine in 0.31 M Methanolic Methoxide 19 5 Product Distributions Resulting from the Photoinitiated Reactions of 0.30 M 3-Iodopyridine with 0.47 - 0.49 M Sodium Thiophenoxide and 0.44 - 0.47 M Sodium Methoxide in Methanol 22 6 Dependence of Product Ratio from the Photoinitiated Reaction of 0.30 M 3-Iodopyridine on the Concentrations of Thiophenoxide and Methoxide Ions 24 7 The Small Effect of Methoxide Ion Con- centration on the Extent of Reaction of 3-Iodopyridine with 1.3 M Sodium Thiophenoxide in Methanol 2 7 8 Product Distributions Resulting from the Photoinitiated Reaction of 1.4 x 10-2 M 3-Iodopyridine with 0.49 M Sodium Thiophenoxide and 0.43 - 0.44 M Sodium Methoxide 29 Vll Table Page 9 Attempted Inhibition of the Photo- initiated Reaction of 0.30 M 3-Iodo- pyridine with 0.47 - 0.49 M Sodium Thiophenoxide and 0.45 - 0.47 M Sodium Methoxide 34 10 Attempted Inhibition of the Photo- initiated Reaction of 1.4 x 10""^ M 3-Iodopyridine with 0.48 M Sodium Thiophenoxide and 0.46 M Sodium Meth- oxide at High Light Intensity 35 11 The Effect of Potential Inhibitors on the Photoinitiated Reaction of 1.4 x 10-2 M 3-Iodopyridine with 0.47 - 0.49 M Sodium Thiophenoxide and 0.44 - 0.47 M Sodium Methoxide at Low Light Inten- sity 36 12 Product Distribution Resulting from the Photoinitiated Reactions of 3- Chloro- and 3-Bromopyridine with Sodium Thiophenoxide and Sodium Meth- oxide 39 13 Product Distributions Resulting from AIBN Initiated Reaction of 3-Iodo- pyridine with Sodiiom Thiophenoxide and Sodium Methoxide in Methanol at 100° for 60 Minutes 46 14 Product Distribution from the Photo- initiated Reaction of 3-Iodopyridine with 0.13 M Phenyl Disulfide in Methanolic Methoxide 50 15 Ultraviolet Absorption Data for 3- lodo- , 3-Bromo-, and 3-Chloropyridine in Methanol 5.5 16 Ultraviolet Absorbence Data for the 3-Halopyridines in Methanol in the Region for Transmittance of Radiation by Pyrex Glass 57 17 Photoinitiated Reaction of 0.30 M 4-Bromoisoquinoline with Sodium Thio- phenoxide and Sodium Methoxide in Methanol 90 Vlll 9 Table Page 18 Photoinitiated Reaction of 0.30 M 3-Bromoquinoline with Sodium Thio- phenoxide and Sodium Methoxide in Methanol 93 19 AIBN Initiated Reaction of 5.9 x 10"2 M 4-Bromoisoquinoline with 0.49 M Thiophenoxide Ion in Methanol 95 20 Photoinitiated Reaction of 0.30 M 2-Iodothiophene with 0.46 - 0.48 M Thiophenoxide Ion in Methanol 97 21 AIBN Initiated Reaction of 5.8 x 10"^ M 2-Iodothiophene with 0.49 M Thio- phenoxide Ion 99 22 Product Distributions from the Irra- diation of 0.30 M 2-Bromothiazole at 71 ± 2° in Methanolic Methoxide which is 0.47 - 0.48 M in Thiophen- oxide 201 23 Product Distributions from the Photo- initiated Reaction of 0.30 - 0.32 M lodobenzene with Sodium Thiophenoxide and Sodium Methoxide in Methanol 106 24 Products Resulting from the Photo- initiated Degradation of 7.1 x 10"'^ M Phenyl Sulfide in 0.62 M Methanolic Methoxide 110 25 Product Distributions from the Photo- initiated Degradation of Phenyl Sul- fide in Methanolic Methoxide in the Presence of 3-Halopyridines 112 26 Product Distributions from the Photo- initiated Reaction of 1.0 x 10"^ M 1-Bromonaphthalene with Sodium Meth- oxide and 0.48 M Sodium Thiophenoxide in Methanol II5 27 Product Distributions from the Photo- initiated Reaction of 0.30 M 1-Bromo- naphthalene with Sodium Methoxide and 0.37 - 0.48 M Sodium Thiophenoxide in Methanol 11 XX Table Page 28 Extent: of Photodegradation of 1-Phenyl- thionaphthalene in the Presence and Absence of 1-Bromonaphthalene in Meth- anol Containing Sodium Methoxide and Sodium Thiophenoxide 122 29 Extent of Photodegradation of 3-Phenyl- thiopyridine in Methanol in the Presence and Absence of Methoxide Ion 125 30 Product Distributions from Photoiniti- ated Reactions of 0.30 M 3-Iodopyridine with Methanolic Methoxide in the Pres- ence of Sulfur Nucleophiles 130 31 Effectiveness of the Anion of 4-Thio- pyridone as a Trap for Phenyl Radical Generated by the Photolysis of lodo- benzene in Methanol 133 32 Product Distributions from Photoiniti- ated Reactions of 0.30 M 3-Iodopyridine with Methanolic Methoxide in the Pres- ence of Phosphorus Nucleophiles 136 33 Results which Demonstrate the Ineffec- tiveness of Carbon, Nitrogen, and Oxygen Nucleophiles as Traps for 3- Pyridyl Radical in Methanol 138 34 Competition Between 0.40 M Thiophen- oxide Ion and Other Thiolate Ions for Aryl and Hetaryl Radicals in 0.28 - 0.31 M Methanolic Sodium Methoxide 141 35 Typical Product Distributions for Com- peting Substitution and Reductive-De- halogenation Reactions Involving a Series of Hetaryl and Aryl Halides 156 36 Calculated Rate Constant Ratios for Reactions of Hetaryl and Aryl a- Radicals with Thiophenoxide Ion and with the Hydrogen Atom Donors Methanol and Methoxide Ion 163 37 A Comparison to Demonstrate the Effect of an Annular Nitrogen Atom on Reac- tivity of o-Radicals Towards Thiophen- oxide Ion 165 X Table Page 38 A Comparison to Demonstrate the Effect of Annelation on Reactivity of a-Radicals Towards Thiophenoxide Ion 167 39 Determination of Labeled Biphenyls Produced by the Irradiation of Phenyl Sulfide in the Presence of Various Additives 185 40 Mass Spectral Analysis (70 eV) of Recovered Phenyl Sulfide from a ^ 475 Minute Irradiation of 7.1 x 10 M Phenyl Sulfide, 0.99 M Benzene-d^, and 0.62 M Sodium Methoxide in Methanol 187 41 Conditions for Unsuccessful Attempts to Thermally Degrade Phenyl Sulfide to Biphenyl 190 42 Isotopic Distribution of Deuterated Biphenyls from the Generation of Phenyl Radical in the Presence of Heavy Benzene and Sodium Methoxide 193 43 Products from the Generation of Phenyl Radical in the Presence of Chlorobenzene 196 44 Photoinitiated Reductive-Dechlorina- tion of p-Chlorobiphenyl in Methan- olic Methoxide 198 45- List of Chemicals and Purification Procedures 219 46 Molar Response Factors and Retention Times for Compounds on Column A 2 33 47 Molar Response Factors and Retention Times for Compounds on Column B 237 48 Molar Response Factors and Retention Times for Compounds on Column C 238 49 Retention Times for Degradation Pro- ducts of AIBN