Two-dimensional correlation infrared spectroscopy of heat-induced esterification of cellulose with 1,2,3,4-butanetetracarboxylic acid in the presence of sodium hypophosphite

The heat-induced esterification reaction between cellulose and 1,2,3,4-butanetetracarboxylic acid (BTCA), catalyzed with sodium hypophosphite (SHP) was investigated by FTIR spectroscopy in combination with the perturbation correlation moving window (PCMW) technique and two-dimensional correlation Infrared spectroscopy (2Dcos). Two main stages could be identified in the heating process between 30 and 160 °C for the reaction system. Weakening of hydrogen bonding interactions within polar groups, such as C=O and O–H, and water evaporation takes place in the first stage (30–100 °C). The reaction process, which consists of cyclic anhydride formation and esterification, between BTCA and cellulose gradually occurs after heating above 100 °C. It is believed that both the presence of SHP and heating, leading to hydrogen bond breakage, contribute to the formation of cyclic anhydrides and further esterification. Moreover, it is shown in the 2Dcos analysis that ester groups appear immediately after the formation of anhydrides, suggesting that the reaction happens in a progressive way. Furthermore, through PCMW maps, we find that the esterification reaction mainly occurs in the temperature region between 126 and 142 °C and is fastest at 132 °C.