Synthesis and structure characterization of soluble starch ethyl carbonates

Starch ethyl carbonates were synthesized applying novel paths including chlorocarbonic acid ethyl ester and ethyl 1H-imidazole-1-carboxylate as reagent. The influence of starch, reaction medium, and base on the degree of substitution (DS) was investigated. The conversion of starch with chlorocarbonic acid ethyl ester in N,N-dimethyl formamide (DMF)/LiCl leads to a preferred substitution of position 6 of the anhydroglucose unit (AGU), on one hand. On the other, the reaction of starch with 1H-imidazole-1-carboxylate in dimethyl sulfoxide (DMSO) or DMF/LiCl results in a preferred functionalization of position 2. The products obtained were well soluble in polar aprotic solvents and in water depending on starch and DS. Intermolecular cross-linking or intramolecular cyclic carbonate formation could not be observed. A detailed structure characterization was carried out by one- and two-dimensional NMR spectroscopy.