Synthesis and use of an immobilized catalyst for the n-oxidation of 2-chloropyridine

N-oxides were defined, their history and chemistry surveyed. Conventional N-oxidising reagents, such as the aliphatic and aromatic percarboxylic acids were examined. Immobilized catalysts, their applications and synthesis were extensively reviewed and examples noted. Immobilized percarboxylic acids or carboxylic acids in conjunction with hydrogen peroxide were identified as potential N-oxidising reagents. The literature survey yielded eight routes which have been utilized for introduction of a carboxyl group into polystyrene. A number of these routes were investigated experimentally. Two routes proved useful, (i) modification of Merrifield resin to carboxylated resin and (ii) chloroacylation of polystyrene , then formation of the phenyl pyridinium chloride derivative followed by cleavage afforded carboxylated polystyrene. The criteria for a useful support resin were reviewed and a porous macroreticular polystyrene-divinylbenzene crosslinked resin was found to offer a number of advantages over convensional gel-type resins. A sample of such a resin, XE-305 was procured from a commercial company and used for synthesis. The carboxylated derivative with carboxylate loading from 42% to 88% were used to oxidise 2-chloropyndine to its N-oxide in the presence of excess hydrogen peroxide and mineral acid. Yields of the order of 33-35% were achieved. 2-Chloropyridine-N-oxide is used for the manufacture of a number of commercially important antifungal and anti- bacterial biocides. Despite numerous changes and modifications to the reaction conditions, including the use of a peroxide stabiliser, the yield could not be increased above 33-35%. For commercial success, yields greater than 60% would have to be achieved inorder to compete with existing processes such as the peracetic acid process reported in the literature. A mass balance examination showed that up to 24% of the initial 2-chloropyridine was unaccounted for at the end of oxidation. A further study of 2-chloropyndine and its N-oxide stability, demonstrated that product N-oxide and not 2-chloropyridine was unstable and decomposed under conditions likely to prevail m the oxidations. No way was found to prevent this decomposition and so it was concluded that this process using immobilized catalyst could not compete with existing batch processes utilising peracetic or acetic acid/hydrogen peroxide