Kinetics and mechanism of the addition of water and ring-opening of 2-methyl- and 2-aryl-4H-3,1-benzoxazines to 2-aminobenzyl esters in the acidic pH range; change in rate-limiting step with buffer concentration and evidence for a tetrahedral carbonyl addition intermediate

Formation of a cyclic tetrahedral intermediate by the addition of water to 2-methyl-4H- 3,1-benzoxazine followed by ring opening to 2-aminobenzyl acetate and 2-acetylaminobenzyl alcohol; pH-dependence of rate of reaction and product ratio

“…The preparations of 2-methyl-4H-3,1-benzoxazine, 2-aminobenzyl acetate, and 2-acetylaminobenzyl alcohol have been described previously (1). Carboxylic acid buffer solutions were made up by partial neutralization of a standardized solution of the carboxylic acid with a standard solution of potassium hydroxide.…”

“…The methods used to study the kinetics of the ring opening of 2-methyl-4H-3,1-benzoxazine to 2-aminobenzyl acetate in the pH range 1-5 have been described previously (1). In the present work, kinetic measurements of the reaction of 2-methyl-4H-3,1-benzoxazine to 2-aminobenzyl acetate and to 2-acetylaminobenzyl alcohol were made at pH values 5-13 at 298.2 K and ionic strength 0.25 mol dm -3 .…”

“…[1] (1). The form of the rate coefficientpH profile and the observation of rectilinear plots of rate coefficient against the concentration of buffer base have identified the mechanism shown in Scheme 1.…”