PREPARATION OF CELLULOSE [1-C-13]ACETATES AND DETERMINATION OF MONOMER COMPOSITION BY NMR-SPECTROSCOPY

A series of cellulose acetates labeled at the carbonyl carbons with carbon-13 was prepared by aqueous acid hydrolysis, metal-catalyzed methanolysis, and acetic acid promoted methanolysis of 2,3,6-tri-([1-C-13]acetyl) cellulose. A total of 16 carbonyl carbon resonances were identified in the carbon-13 NMR spectra of the series of cellulose acetates prepared by aqueous acid hydrolysis. Fewer carbonyl carbon resonances were found in the carbon-13 NMR spectra of the cellulose acetates prepared by metal-catalyzed methanolysis while the carbon-13 NMR spectra of the cellulose acetate prepared by acetic acid promoted methanolysis was very similar to that of a cellulose acetate prepared by aqueous acid hydrolysis. Using the 2D COSY and 1D INAPT experiments, these resonances were assigned to carbonyl carbons attached to either a C2, a C3, or a C6 hydroxyl. In the case of the C2 and C3 carbonyl resonances, these resonances were assigned to specific monomers in the polymer backbone.