Green synthesis of acetylated maize starch in different imidazolium carboxylate and choline carboxylate ionic liquids

This work demonstrates that acetylated maize starches (AMS) with varied degree of substitution (DS, 0.26-2.63) was synthesized in ionic liquids (ILs) (imidazolium chloride, imidazolium carboxylate and choline carboxylate) at 85 C without catalyst. The DS of AMS and reaction efficiency increased with decreasing alkyl chain length of cations or anions, while decreased as the choline cation replaced the imidazolium cation and the chloride anion replaced the acetate anion. The AMS synthesized in imidazolium-based ILs exhibited much higher hydrophobicity and thermal stability than the native starch. Rheological properties of ILs and ATR-FTIR analysis of acetic anhydride/ILs mixtures indicated that a shorter alkyl side chain or the combination of an imidazolium cation and an acetate anion gave ILs lower viscosities and weaker interactions between acetic anhydride molecules, which favored the acetylation of starch. These findings provide insights into the design of green processes to modify starch and the application of acetylated starch.

Automated summary

This study demonstrates the synthesis of acetylated maize starches (AMS) with different degrees of substitution (DS) in the presence of ionic liquids (ILs) without catalyst. The DS and reaction efficiency of AMS increase with decreasing alkyl chain length of cations or anions. AMS synthesized in imidazolium-based ILs exhibit higher hydrophobicity and thermal stability. The viscosity of ILs and the interactions between acetic anhydride molecules are crucial for the acetylation of starch.