Rapid Benzylation of Cellulose in Tetra-n-butylphosphonium Hydroxide Aqueous Solution at Room Temperature
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Abstract:
We found a very fast benzylation of cellulose in a tetraalkyl-onium hydroxide solvent system, 47% tetra-n-butylphosphonium hydroxide aqueous solution. Benzyl cellulose (BC) with a degree of substitution (DS) above 2.5 was obtained within 10 min at ambient temperature (20–25 °C) using ∼9 mol equiv of benzyl bromide to the anhydroglucose unit. The highly efficient benzylation proceeded in the transiently stabilized emulsion state of the reaction system, and the product precipitated out as a solid sediment in the liquid medium. At 20 °C, the benzyl DS was 1.92 after 2 min, and reached 2.40 and 2.53 after 5 and 10 min, respectively. The reaction temperature had a negative correlation with the maximum DS in the explored range of 10–50 °C. No significant degradation of the cellulosic main chain was observed for highly substituted BCs (DS > 2.5). The solubility of BC in common organic solvents was also examined for products with various DSs.Keywords:
Tetra
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Precise measurements with electrochemical cells give specific interaction coefficients of tetra-alkylammonium ions with hydroxide and acetate ions in aqueous solution. Those with the hydroxide ion are useful in further analysis of specific kinetic salt effects of tetra-alkylammonium ions on the hydroxide-ion-catalized depolymerization of diacetone alcohol. Values of the specific interaction coefficients of tetra-alkylammonium cations with anions are tabulated and discussed in relation to corresponding values for alkali metal cations. A qualitative interpretation of trends in the coefficients is given in terms of ion-solvent competition, without invoking so-called "structural" explanations.
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