Ft-Ir and Ft-Raman Spectroscopy Study of the Cyclic Anhydride Intermediates for the Esterification of Cellulose: Ii. Formation of Anhydrides Catalyzed By Sodium Hypophosphite

Abstract

A five-membered cyclic anhydride is the reactive intermediate of polycarboxylic acids for esterifying cellulose. In our previous research, we found that polycarboxylic acids in a crystalline state start to form 5-membered cyclic carboxylic anhydrides when the temperature reaches the vicinity of their melting points, and that hydrogen bonding between carboxylic acid groups prevents the formation of the cyclic anhydride intermediates at lower temperatures. In this research, we studied the formation of cyclic anhydride intermediates by 1,2,3,4-butane-tetracarboxylic acid (BTCA) and itaconic acid (IA) in the presence of sodium hypophosphite (NaH 2 PO 2 ) ' We found that NaH 2 PO 2 weakens the hydrogen bonding between the carboxylic acid groups of BTCA. In the presence of NaH 2 PO 2 , BTCA forms the cyclic anhydride at temperatures significantly lower than its melting point. NaH 2 PO 2 also reduces the temperatures required for the formation of the anhydride intermediate of IA on cotton fabric. The catalysis for the formation of anhydride intermediates by NaH 2 PO 2 contributes to the acceleration of esterification of cotton cellulose by polycarboxylic acids.