SOLVENT EFFECTS ON CHEMICAL PROCESSES .8. DEMETHYLATION KINETICS OF ASPARTAME IN BINARY AQUEOUS-ORGANIC SOLVENTS

The kinetics of demethylation of aspartame were studied in binary aque ous-organic solvent mixtures at 25 degrees C under two solution condit ions, namely 1.0 M HCl (pH 0.28 in water) and carbonate buffer (pH 10. 1 in water). Under these conditions solvent effects on the acid dissoc iation constants of aspartame do not complicate the interpretation of the kinetics. The organic cosolvents were acetone, acetonitrile, dimet hyl sulfoxide, dioxane, tetrahydrofuran, and methanol. The observed ki netic solvent effects were modest in magnitude, not exceeding a factor of 3 in rate constant, relative to the fully aqueous solution. The ra te changes included both increases and decreases, and in some solvent mixtures extrema were observed. It is concluded that at least two cont ributory factors, identified as an electrostatic (dielectric constant) effect and a solvation effect, must be operating to produce the obser ved kinetic solvent effects.