Kinetic studies have shown that addition of water to protonated 2-methyl-4H-3,1-benzoxazine occurs to give a cyclic tetrahedral carbonyl addition intermediate. At pH <5, the intermediate is protonated and reacts to 2-aminobenzyl acetate, whereas at pH >7.5, the unprotonated intermediate collapses to give 2-acetylaminobenzyl alcohol. The former reaction is catalysed by buffer base but the latter is uncatalysed. At pH 9-12, reaction of hydroxide ion with protonated 2-methyl-4H-3,1-benzoxazine to give 2-acetylaminobenzyl alcohol becomes important, and at pH >12, the same product is formed by reaction of hydroxide ion with unprotonated 2-methyl-4H-3,1-benzoxazine.Key words: mechanism, addition, tetrahedral intermediate, hydrolysis, pH profile.
动力学研究表明,将水加入质子化的2-甲基-4H-3,1-苯并噁嗪中会产生一个环四面体羰基加成中间体。在pH<5时,中间体被质子化并反应为2-氨基苄酸乙酯,而在pH>7.5时,未质子化的中间体崩解为2-乙酰氨基苄醇。前者的反应由缓冲碱催化,而后者则未催化。在pH 9-12时,氢氧化物离子与质子化的2-甲基-4H-3,1-苯并噁嗪反应生成2-乙酰氨基苄醇变得重要,而在pH>12时,氢氧化物离子与未质子化的2-甲基-4H-3,1-苯并噁嗪反应生成相同的产物。关键词:机理,加成,四面体中间体,水解,pH值。