SUBSTITUENT AND SOLVENT ISOTOPE EFFECTS ON THE REACTION OF 2-ALKYLNAPHTH[1,8-DE]-1,3-OXAZINES TO 1-HYDROXY-8-ACYLAMINONAPHTHALENES THROUGH REVERSIBLE FORMATION OF A CYCLIC TETRAHEDRAL ADDITION INTERMEDIATE

The first-order rate coefficient for the addition of water to substitu ted 2-alkylnaphth[1,8-de]-1,3-oxazines to give the corresponding 1-hyd roxy-8-acylaminonaphthalenes in aqueous solution at pH 0 to ii goes th rough a maximum value with pH. Substituent effects and Solvent isotope effects on the rate-pH profile-are explained by a mechanism involving reversible addition of water to the protonated naphthoxazine to give a cyclic tetrahedral intermediate and hydronium ion followed by ring-o pening of the intermediate to form product. In aqueous alkaline soluti on and in 50% (v/v) Me(2)SO-H2O containing hydroxide ion the reaction is first-order with respect to hydroxide ion and involves nucleophilic addition of hydroxide ion to the neutral naphthoxazine.