Novel insights into hydrocarbon oxidation

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 fundamental problems of this free radical chain reaction are reviewed, and particular attention is given to recent studies by Ishii, who has introduced N-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 from 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-butyl 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 aN value of the derived nitroxide radicals could be correlated with its ability to abstract a hydrogen atom from 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 N-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