Acid-catalyzed hydrolysis of tetramethoxyethene in aqueous solution. Initial state stabilization by the methoxy groups

Abstract

The acid-catalyzed hydrolysis of tetramethoxyethene to methyl dimethoxyacetate in aqueous solution at 25 °C was found to occur with the hydronium-ion catalytic coefficient [Formula: see text], to give the solvent isotope effect [Formula: see text], and to provide a Brønsted relation based upon six carboxylic acids with the exponent α = 0.42. These data indicate that the reaction proceeds via rate-determining proton transfer from the catalyzing acid to an olefinic carbon atom of the substrate. They also show tetramethoxyethene to be 1.0 × 106 times less reactive than 1,1-dimethoxyethene (ketene dimethyl acetal), a rate retardation 600 times greater than that expected from initial state stabilization by the two additional methoxy groups in tetramethoxyethene; possible causes of this disparity are discussed. Keywords: tetramethoxyethene, carbon–carbon double bond reactivity, ketene acetal, vinyl ether hydrolysis.