The Kinetics of Cyanoethylation of Methanol in Mixed Methanol-Aprotic Solvents

The kinetics of the cyanoethylation of methanol catalyzed by alkali metal methoxides was studied in solvent mixtures of methanol and the aprotic solvents dimethyl sulfoxide, dimethylformamide, dimethylformamide-dioxane (1:1), dioxane, tetrahydrofuran, and benzene. The rate of reaction was first order in acrylonitrile, first order in the alkali metal methoxide, and was proportional to l/[CH₃OH]ⁿ, n being dependent on the aprotic solvent. It increased with increasing the concentration of the aprotic solvent in the solvent mixture, owing to its participation in the equilibrium reactions leading to desolvation of methanol-solvated methoxide ions. This enhancement was especially pronounced at low methanol concentrations. Depending on the aprotic solvent, the rate of reaction decreased in the order dimethyl sulfoxide > dimethylformamide ≫ tetrahydrofuran ≃ dioxane > benzene.