Studies About the Solvent‐Dependent Substitution Pattern of Starch Acetates

Starch acetates bearing the ester moiety predominantly at position 2 of the anhydroglucose unit (AGU) could be synthesized by converting starch with acetic anhydride and imidazole in dimethyl sulfoxide (DMSO). Degraded starch (weight average molar mass,M ‾ w  < 16 460 g mol −1 ) is additionally acetylated at position 6 exceeding a total degree of substitution (DS) of 0.5. Increasing the concentration of starch up to 50 wt% leads to higher partial DS at position 6 under comparable reaction conditions. Using molten imidazole as solvent, an initial regioselective 6‐ O ‐acylation is achieved. At higher DS values (>0.3), a random distribution of the substituents appears. The substitution pattern can be revealed precisely by means of 13 C and 1 H NMR spectroscopy after perpropionylation. Hydrolytic stability of a selected 2‐ O ‐acetyl starch in aqueous solution is evaluated by time‐dependent capillary viscosimetry.