Polymeric peracids, oxidation

Polymer-supported reagent. A polymeric peracid reagent (1) has been prepared from a polystyrene resin cross-linked with 1 or 2% of divinylbenzene by chloromethylation and oxidation to give a resin substituted by carboxyl groups. The —COOH groups are then converted into —COOOH groups by treatment... 

Poly (ethyl vinyl ether) (PEVE) macromonomers were also prepared using initiator 5 bearing an allylic function [148]. This reactive group remained intact during the polymerization and could be transformed into the corresponding oxirane by peracid oxidation. 

Percarboxylic acids have been used widely in Baeyer-Villiger oxidation. Peracetic acid is one of the most commonly used peracids distilled peracetic acid is employed commercially by Solvay Interox for the production of e-caprolactone.246 The use of distilled peracetic acid is essential, as it contains no strong protic acids which can catalyse polymerization of the resulting lactone and cause other side reactions. Figure 3.53 illustrates the use of pre-formed peracetic acid for the Baeyer-Villiger oxidation of ketones.247,248... 

Another possibility for enhaneing the selectivity toward epoxides is use of the urea-H202 (UHP) adduct. This enables the oxidation to be carried out in water-free solutions, thus avoiding formation of any diols and other side reactions. In the case of the oxidation of chiral allylic alcohols (see below) high diastereo-selectivities have been achieved [3]. The ability to transform olefins to epoxides diastereoselectively seems to indicate that the reaction proceeds through a peracid-like transition state. However, a drawback of the urea-H202 system is the insolubility of the polymeric complex. 

In the case of the oxidation of unsaturated aldehydes, the investigation is complicated by the fact that the aldehyde and the acid resulting from the transformation of peracid are liable to become polymerized. The double bond in a position a to the carbonyl group is not very reactive with regard to peracid, and so there is no epoxidation. 

Polymeric percarboxylic acids (33) have been prepared from PS analogues of benzoic acid and benzoyl chloride as in equation (13). Expoxides are formed from di- and tri-substituted alkenes with (33) at 40 °C. The PS-peracids also oxidized sulfides to mixtures of sulfoxide and sulfone, and with penicillins and deacetoxycephalosporins gave sulfoxides in high yield. 

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