Investigations on esterification reactions of starches in 1-N-butyl-3-methylimidazolium chloride and resulting substituent distribution

The ionic liquid (IL) 1-N-butyl-3-methylimidazolium chloride ([C₄mim]⁺Cl⁻) was used as solvent for different esterification reactions of the biopolymer starch. Therefore, maize starches with varying content of amylose were used. Different carboxylic acid anhydrides were applied to esterify starch with a degree of substitution (DS) in the range of 0.7-3.0. For example, starch acetates with the mentioned DS are accessible within 30 min at a 105°C-reaction temperature. The DS distribution of starch acetates synthesized in IL was compared with the common starch acetate synthesis of Mark and Mehltretter. Also, a consideration of starch acetates and cellulose acetates synthesized in [C₄mim]⁺Cl⁻ is given. The starch esters were characterized by means of Raman spectroscopy for qualitative- and nuclear magnetic resonance spectroscopy for quantitative determination of the functionalization pattern. Moreover, the molecular mass distribution was determined after saponification by means of GPC-MALLS.