Kinetics of the intramolecular displacement of alcohols from o-hydroxyaminobenzoates

Abstract

The kinetics of the liberation of benzyl and aliphatic alcohols from esters of o-hydroxyaminobenzoic acid, with formation of 2,1-benzisoxazol-3(1H)-one, have been investigated in acidic and in basic solution. In alkaline solution the reactions are very rapid, the displacement of the alcohol from the hydroxyamino-esters in dilute alkali occurring ca. 10⁴ times more rapidly than from the corresponding unsubstituted benzoates. The observed kinetics are consistent with a rate-determining reaction between the anion of the hydroxyamino-group and the neighbouring ester group, with the pK_a for the ionisation of the hydroxyamino-group in the various esters close to 12.0. The reactions are considerably slower in acid solution, but comparison with the acid-catalysed hydrolysis of unsubstituted benzoates again suggests direct involvement of the hydroxyamino-group. The pK_a of the product benzisoxazolone, is 7.63.