STUDIES ON THE MECHANISM OF OXIME AND SEMICARBAZONE FORMATION
STUDIES ON THE MECHANISM OF OXIME AND SEMICARBAZONE FORMATION
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DOI：
10.1021/ja01511a053
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发表时间：
1959-01-01
影响因子：
15
通讯作者：
JENCKS, WP
中科院分区：
文献类型：
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作者：
JENCKS, WP
在中性pH下，羟胺和氨基脲与许多醛和酮迅速反应形成加成化合物，其缺乏原始羰基化合物的紫外和红外吸收。这些加成化合物在酸催化下缓慢脱水生成肟或缩氨基脲。在酸性pH下肟形成速率的降低似乎是由于过渡到自由氮碱对羰基化合物的限速攻击，而不依赖于一般的酸催化。加成络合物的脱水、水与肟或缩氨基脲的加成以及氨基脲与羰基的加成都受到特定的和一般的酸催化作用，而强碱羟胺与羰基的加成仅在很小程度上受到特定的酸催化作用。4和West-heimer 5证明了羰基化合物与羟胺和氨基脲等氮碱的反应在其pH-速率曲线上显示出显著的极大值。这些pH最佳值归因于一般酸催化的相反作用和浓度的降低。
At neutral pH hydroxylamine and semicarbazide react rapidly with a number of aldehydes and ketones to form addition compounds which lack the ultraviolet and infrared absorption of the original carbonyl compound. These addition com-pounds undergo a slow, acid-catalyzeddehydration to form oxime or semicarbazone. The decrease in the rate of oxime formation at acid pH appears to be due to a transition to a rate-limiting attack of free nitrogen base on the carbonyl com-pound and is not dependent on general acid catalysis. Dehydration of the addition complex, addition of water to the oxime or semicarbazone and addition of semicarbazide to the carbonyl group are subject to both specific and general acid catalysis, while the addition of the stronger base, hydroxylamine, to the carbonyl group is specific acid-catalyzed to only a small extent.The classical experiments of Barrett and Lapworth, 2 Olander, 3 Conant and Bartlett, 4 and West-heimer5 demonstrated that the reactions of car-bonyl compounds with such nitrogen bases as hydroxylamine and semicarbazide exhibit striking maxima in their pH-rate profiles. These pH op-tima have been attributed to the opposing effects of general acid catalysis and the decrease in the con-