Acylation. Part XXIII. Cyclic transition states in acylation by ketens

Abstract

The acylation of m-chloroaniline by dimethylketen in ether is catalysed by the addition of powerful tertiary bases, but such bases are relatively much less effective catalysts than is a second m-chloroaniline molecule. It is argued that while the function of tertiary bases can only be to render the attacking aniline more nucleophilic, by partially accepting a proton from it in the transition state, the relatively great effect of a second aniline molecule arises from its ability both to accept and to donate protons in a cyclic transition state [e.g., (B) and (E)]. Small concentrations of polymeric basic species are implicated as the reacting entities. Kinetic data for the spontaneous N-acylation of anthranilic acid by dimethylketen fit the equation Rate =k[Anthranilic acid]²[Keten]. The value of k shows that the intermolecular catalysis by the second anthranilic acid molecule is virtually entirely due to its carboxy- and not to its amino-group.