VINYL ETHER HYDROLYSIS. 30. EFFECT OF β-CARBOXY AND β-CARBOMETHOXY SUBSTITUTION

Article abstract of DOI:10.1002/poc.610070608

Rates of hydrolysis of the vinyl ether functional groups of (Z)- and (E)-β-methoxyacrylic acid and (Z)- and (E)-β-methoxymethacrylic acid and their methyl esters were measured in aqueous perchloric acid solution.Additional rate measurements were also made for one substrate, (Z)-β-methoxymethacrylic acid, in buffer solutions down to pH 7, and a rate profile was constructed.The results show that the β-carboxy and β-carbomethoxy substituents produce strong rate retardations, ranging from 2000- to 25 000-fold, for both Z- and E-isomers in both the acrylic and methacrylic acid series.The rate profile for (Z)-β-methoxymethacrylic acid indicates that ionization of this substrate to the carboxylate ion form raises the rate of hydrolysis by a factor of 240.It is argued that this difference in reactivity of ionized and non-ionized forms of the substrate is due to conjugative and inductive effects of the substituents, rather than β-lactone formation as suggested in an earlier observation of the same phenomenon in a different system.