Design and applications of a solid-phase oxidizing reagent consisting of a crosslinked polystyrene matrix and a t-butyl hypochlorite function separated by a trimethylene spacer

Abstract

A crosslinked polystyrene–supported solid-phase analogue of t-butyl hypochlorite containing a trimethylene spacer group between the polymer matrix and the t-butyl hypochlorite function was prepared and used as a recyclable oxidizing reagent for alcohols. The synthetic route to this new polymeric reagent involved a seven-step polymer-analogous reaction starting from styrene-divinyl benzene 2%-crosslinked polymer. A β-ketopropionic acid function was introduced into the polystyrene matrix by Friedel–Crafts reaction with succinic anhydride. The keto function in the resulting polymer (2) (capacity, 3.57 meq of COCH₂CH₂COOH/g) was converted to the methylene group by Clemmensen reduction using zinc amalgam and HCl. The carboxyl function in the product polymer (3) was converted to the acylmalonic ester function by malonic ester synthesis through the reaction of the polymeric acid chloride (4) with ethoxymagnesium diethylmalonate. The polymeric acyl malonic ester (5) was decarboxylated to yield the 2-oxopentyl polystyrene resin (6). This on Grignard reaction with methyl magnesium iodide followed by hydrolysis afforded the polystyrene derivative with the t-butyl alcohol function separated by three methylene groups (7). The t-butyl alcohol resin (7) was converted to the corresponding hypochlorite resin (8) by reaction with sodium hypochlorite. The resin was found to have a capacity of 2.84 mmol Cl/g by iodometric analysis. The capacities of the resins 2-8 were determined from the weight changes in the corresponding conversions and verified by quantitative determination of the functional groups. This new hypochlorite was found to oxidize alcohols to carbonyl compounds in 85-98% yield. The oxidizing efficiency of this new reagent was found to be significantly greater than those of the reagents containing only one spacer and no spacer between the reagent function and the polymer support. The presence of a 3-methylene spacer also facilitated the hypochlorite formation step significantly.