Interaction of meso-1,2,3,4-Butanetetracarboxylic Acid with Phosphorus-Containing Catalysts for Esterification Cross-Linking of Cellulose

In the presence of catalysts, polycarboxylic acids such as meso -1,2,3,4-butanetetracarboxylic acid (BTCA) can cross-link cellulose in a process believed to involve cyclic anhydrides as intermediates. This study was undertaken to explore, in the absence of cellulose, interactions between catalysts and polycarboxylic acids that might explain the catalysts' role. Aqueous solutions containing equimolar amounts of BTCA and a catalyst (NaH 2 PO 4 or NaH 2 PO 2 ) were evaporated to constant weight. The residues were subjected to thermal analysis and to infrared spectroscopic analysis after heating. As the BTCA−NaH 2 PO 4 residue was heated, the BTCA remained complexed with phosphate until a monoanhydride formed the same monoanhydride that formed when BTCA alone was heated to a higher temperature. In the BTCA−NaH 2 PO 2 system an anhydride apparently formed at an even lower temperature than in the phosphate-containing system but then reacted with the hypophosphite.