Hydrolysis of Hydroxypropyl Methylcellulose by Trifluoromethanesulfonic Acid and Subsequent Determination of Chemical Structure by 13C NMR Spectroscopy

The hydrolysis of three hydroxypropyl methylcellulose samples with varying degrees of polymerization by aqueous solutions of trifluoromethanesulfonic acid with a concentration of 1, 2, 3, and 4% at a temperature of 80, 90, 100, and 110°C in a microwave reactor is studied. The completeness of hydrolysis is estimated by 13C NMR spectroscopy of the disappearance of the signal the acetal carbon atom. It is shown that the concentration of acid has the greatest influence on the hydrolysis rate, the effect of temperature increase is not so strong, and the effect of reaction time is even smaller. Using 13C NMR spectroscopy, substitution parameters at the second, third, and sixth positions (DSC-2, DSC-3, and DSC-6) are determined, the amount of methyl (DSMe) and hydroxypropyl groups (DSHP) is estimated, and the total degree of substitution (DStotal) is calculated.