Halogenation of ketones with N-halosuccinimides under solvent-free reaction conditions
作者:Igor Pravst、Marko Zupan、Stojan Stavber
DOI:10.1016/j.tet.2008.03.048
日期:2008.5
Several aryl substituted ketones, cyclic ketones, 1,3-diketones and a β-ketoamide were halogenated with N-halosuccinimides under solvent-free reaction conditions (SFRC) at various temperatures (20–80 °C), whereas less enolized ketones required the presence of an acid catalyst (p-toluenesulfonic acid, PTSA). Bromination of substituted acetophenones obeys first order kinetics v=kBr[ketone] and the following
在无溶剂反应条件下(SFRC),在各种温度(20-80°C)下,将N-卤代琥珀酰亚胺卤代数个芳基取代的酮,环酮,1,3-二酮和β-酮酰胺,而较少烯醇化的酮则需要存在酸催化剂(对甲苯磺酸,PTSA)。取代的苯乙酮的溴化反应遵循一级动力学v = k Br [酮],并与酮-烯醇平衡常数具有以下相关性:log k Br = 0.3p K E + C 1,少酚化的底物更具反应性;在速率确定步骤中产生的适度正电荷已通过Hammett相关性得到证实(ρ = -0.5)。另一方面,在环状酮中观察到相反的关系:log k Br = -0.6p K E + C 2,表明具有较高烯醇化常数(K E)的底物具有较高的反应性。发现在SFRC溴化之前,溶剂(MeCN,MeOH)的性质在酮-NBS-PTSA混合物的预组织中起着重要作用。