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c ^ 7 Novel Insights into Hydrocarbon Oxidation A Thesis presented by Camilla Corsi In Partial Fulfilment of the Requirements for the Award of the Degree of DOCTOR OF PHILOSOPHY OF THE UNIVERSITY OF LONDON Department of Chemistry University College London 20 Gordon Street London WCIH OAJ May 2003 ProQuest Number: U643863 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest. ProQuest U643863 Published by ProQuest LLC(2016). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. Microform Edition © ProQuest LLC. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 To my parents, Abstract The present thesis is concerned with the development of a high conversion-high selectivity alkane oxidation process, which employs molecular oxygen, operates under mild conditions, and is accordingly based on autoxidation as the simplest conceptual approach. In the first chapter, the subtleties and fimdamental problems of this fi-ee radical chain reaction are reviewed, and particular attention is given to recent studies by Ishii, who has introduced 7V-hydroxy phthalimide (NHPI) and its derived nitroxide (PINO) as a relay catalyst system to increase efficiency. The behaviour of PINO, both in its ability to abstract a hydrogen fi*om an alkane but not act as an alkyl radical trap, together with the apparently unfavourable thermodynamic situation consequently focussed our research work in this area. For reasons of clarity in presentation, the second chapter, which outlines and discusses the results obtained in our studies, is divided into two parts. The first of these describes a study involving the addition of “onium salts” in the presence of traces of water which led to the discovery of a new method using tert-h\xiy\ hydroperoxide in the absence of NHPI. Efforts to rationalise conflicting literature results in this area were made using ah initio theory but no clear mechanistic insight into these curious but real phenomena emerged. In the second section of the results and discussion, a variety of possible NHPI replacements were screened on the hypothesis that the a// value of the derived nitroxide radicals could be correlated with its ability to abstract a hydrogen atom fi*om an alkane. Four classes of compounds, each of which possessed electron withdrawing groups adjacent to the hydroxylamine moiety were considered including sulfonyl, difluoromethylene and acyl nitroxides together with a variety of N- heterocyclic systems. Two of these systems, an W-hydroxypyridone and an “indigo type” dimer have provided interesting leads for further study. The thesis concludes with a final chapter outlining the experimental procedure used and the characterisation of the compounds prepared. Contents Table of Contents Abstract pag. 1 Contents pag. 2 Acknowledgements pag. 4 Abbreviations pag. 5 CHAPTER 1. INTRODUCTION pag. 9 CHAPTER 2. RESULTS AND DISCUSSION pag. 39 2.1 Introduction pag. 39 2.2 The “Onium salt” effect pag. 40 2.2.1 Observations on the anionic component of the onium salt in Ishii’s system and related oxidations pag. 40 2.2.2 The nature of the onium salt cation pag. 51 2.2.3 Decomposition studies using tert-huXyX hydroperoxide pag. 59 2.2.4 Observations on the behaviour of di-^err-butyl peroxide pag. 62 2.2.5 The use of ionic liquids as phase-transfer catalysts pag. 66 2.2.6 CDS: Cambridge Crystallographic Database pag. 68 2.2.7 Quantum Mechanics Calculations pag. 69 2.2.8 Potential intramolecular variants pag. 76 2.2.9 Summary and conclusions pag. 85 2.3 Alternatives to NHPI and PINO pag. 88 2.3.1 Sulfonated nitroxides pag. 88 2.3.1.1 The use of Fremy’s salt pag. 89 2.3.1.2 The preparation of 2-hydroxybenzo[l,3,2]dithiazole 1.1.3.3 tetraoxide pag. 93 2.3.1.3 NHS: A-hydroxysaccharin pag. 102 Contents 2.3.2 Generation of difluoromethylene substituted A^^-hydroxylamines pag. 104 2.3.2.1 Barton ester chemistry pag. 105 2.3.2.2 Ene reactions pag. 109 2.3.2.3 The use of nitrosyl chloride with olefins pag. 118 2.3.3 Acyl nitroxides and related derivatives from benzohydroxamic acid pag. 121 2.3.3.1 Derivatisation of benzohydroxamic acid pag. 121 2.3.3.2 Conjugated nitroxides pag. 129 2.3.4 Heterocyclic precursors pag. 137 2.3.4.1 Indole and pyridone structures pag. 137 2.3.4.2 Generation of 1-hydroxyoxindole pag. 138 2.3.4.3 [1+4] Cycloaddition pag. 150 2.3.4.4 The use of 1 -hydroxy-7-azabenzotriazole pag. 153 2.3.4.5 1,2-Dihydro-1-hydroxy-4,6-dimethyl-2-oxopyridine 3-carbonitrile pag. 154 2.3.5 Conclusions and Perspectives pag. 164 CHAPTER 3. EXPERIMENTAL pag. 170 Appendix pag. 220 References pag. 241 Acknowledgements I would like to thank my supervisor, Prof. Willie Motherwell, for giving me the opportunity to work on this challenging project, and for his help during the revision of this manuscript. Thanks also to Dr. Simon Ellwood from Quest International for his support and expertise. My project covered a broad range of topics, and as a result there are several people whose help and advice was invaluable in learning such useful and diverse techniques. Three people in particular deserve special thanks: Prof Clary and Dr. T. Van Mourik for their enormous patience when teaching me about ab initio calculations and molecular modelling studies, and Dr. Robyn Motherwell who showed me the value and potential of ESR. I would also like to thank Prof. B. Roberts for letting me use the Varian E-109 instrument and Dr. H. Rzepa at Imperial College for the CDS studies. I also thank all the technical staff at UCL for their help: Jill Maxwell for the microanalyses, John Hill for the mass spectra and the amazing NMR team: Dr. Abil Aliev (the boss). Dr. Jorge Gonzales and David Butler. The painstaking work of proof readers Beatrice, Oliver, Robyn and Steve is also greatly appreciated. However, this experience would not be as memorable without meeting in the past three years many talented chemists from so many different countries. From my first year, thanks to Christoph, Julien and Rosa who mentored me in the lab and with whom I shared great experiences outside UCL and Lynda for her contagious smile which never failed to cheer me up. Thanks to Oliver, always full of advice and ready to discuss everything with one with genteel humility. Thanks to my sympathetic bench mate Rehan who successfully dealt with my character and never complained about infringements of the fume hood border. Thanks to Catherine for the enjoyable chats and time, which rapidly improved my English and Beatrice who was the best mate I could wish for and with whom I shared both good and bad times during this PhD. Other people that make my time in the lab a pleasant experience are Géraldine, Stéphane, Steve, Charlotte, Karim, Marta, Susana, Guillaume, Ela, Joëlle and certainly Rob and anyone else I may have omitted. Finally, I thank my family for their continued love, support and encouragement. Of course, all this would not be possible without them, which is why I would like to dedicate this thesis to them. Abbreviations ABBREVIATIONS and DEFINITIONS 13 C-NMR Carbon Nuclear Magnetic Resonance 19 F-NMR Fluorine Nuclear Magnetic Resonance 'H-NMR Proton Nuclear Magnetic Resonance ^‘P-NMR Phosphorus Nuclear Magnetic Resonance AcOH Acetic acid Aliph. Aliphatic AIBN Azodiisobutyronitrile aq. Aqueous Ar Aryl atm Atmosphere br Broad Bn Benzyl b.p. Boiling point BSA Bis-trimethylsilyl acetamide r-Bu tert-^\xXy\ r-BnOOH ^er^-butyl hydroperoxide ^-BuOO-Bu-? tert-h\xXy\ peroxide cat. Catalytic amount cone. Concentrated conv. Conversion COSY correlated SpetroscopY CPMASS TOSS Cross Polarisation Magic Angle Spinning, Total Suppression of Spinning Side Bands Cq Quaternary carbon d Doublet A Heating DAST Diethylaminosulfur trifluoride DBU l,8-Diazabicyclo[5.4.0]undec-7-ene DCC V, V -dicyclohexylcarbodiimide DMD Dimethyldioxirane DCM Dichloromethane DMF Dimethylformamide Abbreviations DMSO Dimethyl sulfoxide EDCl 4-Dimethylaminopropyl-3-ethyl carbodiimide hydrochloride EDG Electron Donating Group ee Enantiomeric excess El Electron Impact ESR Electron Spin Resonance equiv. Molar Equivalents Et Ethyl EtiO Diethyl ether EtOAc Ethyl acetate EtOH Ethanol EWG Electron Withdrawing Group FAB Fast Atom Bombardment GC Gas Chromatography h Hour HF Hartree-Fock HMBC Heteronuclear Multiple Bond Connectivity HMDS Hexamethyldisilazane HMQC Heteronuclear Multiple Quantum Coherence HRMS High Resolution Mass Spectrometry r Initiator radical Imid Imidazolium IR Infra Red J Coupling constant lit. Literature m multiplet m Meta Me Methyl MeOH Methanol min Minute m.p. Melting Point NHS A-hydroxysaccharin Abbreviations NHPI //-hydroxyphthalimi de a Ortho P Para PE Petroleum ether Ph Phenyl PINO iV-oxyphthalimide ppm Parts per million PTC Phase-Transfer Catalyst pyr Pyridine q Quartet r.t. Room temperature s Singlet sat. Saturated sec Secondary SET Single Electron Transfer SM Starting material sp. gr. Specific gravity t Triplet t Tertiary TAS-F Tris(dimethylamino)sulfur(trimethylsilyl)difluoride TBAB Tetra-M -butyl ammonium bromide TBAF Tetra-M-butylammonium fluoride TBAT T etra-M -butyl ammonium tripbenyldifluorosilicate TEMPO 2,2,6,6-T etrametbyl-1 -piperidinyloxy T f Triflate TEA Trifluoroacetic acid TFAA Trifluoroacetic anhydride THF Tetrabydrofuran THP T etrabydropyranyl TMEDA T etrametbyletbylenediamine tic Thin layer chromatography TMS Trimetbylsilyl UV Ultra Violet w/v Weight per volume Abbreviations Conversion : amount of reactant consumed in a chemical process, expressed as a percentage relative to the original charge.