Rapid preparation of starch maleate half-esters

Abstract

A novel method for the rapid preparation of starch esters is described herein, by rapid heating using microwave or conventional means. A 5-min method to prepare starch maleates with degree of substitution (DS) up to 0.25 was developed when microwave or conventional source assisted fast heating of starch in dimethyl sulfoxide (DMSO) reacted with 0.5 equiv. maleic anhydride in the presence of 0.5 equiv. of pyridine with a reaction efficiency of 50%. For a given amount maleic anhydride higher amount pyridine gave higher DS. The reactivities of maleic and succinic anhydrides were compared. Succinic anhydride/starch gave DS of 0.3 as compared to only 0.1 with maleic anhydride/starch. The effects of varying reaction time, microwave power, anhydride and pyridine amount on the reaction yield and composition were studied. Proton NMR and IR were used to determine the DS. Instead of microwave when reactions were heated with a conventional heat source, starch esterification reactions gave starch maleate with lower DS.