Highly Selective Mitsunobu Esterification of Cellulose with Hydroxycinnamic Acids

Abstract

Cellulose esters of hydroxycinnamic acids, namely ferulic-, p-coumaric-, and caffeic acid, are synthesized by Mitsunobu esterification applying triphenylphosphine and diisopropyl azodicarboxylate in N,N-dimethylacetamide/LiCl. The reaction is found to be highly selective and took place at primary hydroxyl groups at position 6 of cellulose without undesired conversion of double bonds and phenolic hydroxyl groups. Molecular structure characterization is performed by FTIR- and NMR spectroscopy. The products are soluble in dimethyl sulfoxide and possessed degree of substitution (DS) values of up to 0.5. DS values are determined by two independent methods, namely 1H NMR spectroscopy of peracetylated derivatives and UV spectroscopy of extracted ferulic acid. The synthesis of cellulose hydroxycinnamates is very important to design lignocellulosic model systems and antioxidative bioinspired materials.