Reactivity and Acid−Base Behavior of Ring-Methoxylated Arylalkanoic Acid Radical Cations and Radical Zwitterions in Aqueous Solution. Influence of Structural Effects and pH on the Benzylic C−H Deprotonation Pathway
作者:Massimo Bietti、Alberto Capone
DOI:10.1021/jo060678i
日期:2006.7.1
the radical cations or radical zwitterions undergo benzylic C−H deprotonation as the exclusive side-chain fragmentation pathway, as clearly shown by product analysis results. At pH 1.7, the first-order deprotonation rate constants measured for the ring-methoxylated arylalkanoic acid radical cations are similar to those measured previously in acidic aqueous solution for the α-C−H deprotonation of structurally
在不同的pH值下,对环甲氧基化的苯丙酸和苯丁酸(Ar(CH 2)n CO 2 H,n = 2、3)进行单电子氧化的产物和时间分辨动力学研究。氧化导致芳族基团的阳离子的形成(AR • +(CH 2)Ñ CO 2 H)或基团的两性离子(AR • +(CH 2)ñ CO 2 - ),这取决于pH值,且p ķ一个已测量了相应的酸碱平衡值。在自由基阳离子中,通过增加甲氧基环取代基的数目和通过增加羧基与芳环之间的距离,羧基质子的酸度降低。如产物分析结果清楚地显示,在pH值为1.7或6.7时,自由基阳离子或两性离子会经历苄基CH去质子化,作为唯一的侧链断裂途径。在pH 1.7下,对环甲氧基化的芳基链烷酸自由基阳离子测得的一阶去质子化速率常数与先前在酸性水溶液中对与结构相关的环甲氧基化的烷基芳族自由基阳离子的α-CH脱质子化所测得的常数相似。在基本解决方案中,获得了-OH(k - OH)。这些值类似于针对