Selective reactivities and accessibilities of the hydroxyl groups in cotton cellulose based on equilibrium data from a reversible chemical reaction

In order to determine the relative equilibrium constants for reactions of the hydroxyl groups at C₂, C₃, and C₆ of the D-glucopyranosyl units, methyl vinyl sulfone was reacted with cellulose dissolved in benzyltrimethylammonium hydroxide. The reaction was carried to constancy in distribution of substituents between the 2–0– and 6–0–positions. The distributions of substituents in the D-glucopyranosyl units were measured by gas-liquid chromatographic analysis of the products from hydrolysis of the modified cellulose. Relative equilibrium constants were then evaluated, assuming complete accessibility of all three types of hydroxyl groups of the cellulose in solution. For determination of the relative accessibilities of the individual types of hydroxyl groups in heterogeneous reactions of cotton cellulose with methyl vinyl sulfone, the reactions were carried to equilibrium distributions in media of various normalities of sodium hydroxide (i.e., media of various swelling strength). The distributions of substituents in the D-glucopyranosyl units were measured. From these values and the ratio of equilibrium constants, the relative accessibilities of the hydroxyl groups at C₂ versus those at C₆ were calculated. Apparent accessibilities of the hydroxyl groups at C₂ are approximately double those at C₆ when the reaction is carried out in 1N sodium hydroxide and about triple those at C₆ when the reaction is carried out in 0.5N sodium hydroxide.