Comparison of reactions of radical cations of 1-phenylalkanols produced by photoionization and by one-electron oxidation in aqueous solution
作者:Steen Steenken、Ramasamy Ramaraj
DOI:10.1039/b102515p
日期:——
Benzyl alcohols in aqueous solution react with photo- and radiation-chemically produced ˙OH and SO4˙− radicals with diffusion-controlled rates to yield OH-adducts and benzyl alcohol radical cations, respectively. The former can be converted to the radical cations by H+-induced (heterolytic) dehydroxylation, whereas the latter decay by a) electrophilic reaction with water (= reverse of the dehydroxylation reaction) giving rise to Cnucleus–OH-adducts and by b) side chain C–H deprotonation yielding α-hydroxybenzyl-type radicals. If, however, the radical cation is produced by biphotonic ionization of the benzyl alcohol, the pattern of Cnucleus–OH bond formation and side chain C–H bond breakage is different from that in the reaction with SO4˙−. It is concluded that, at least in this reaction, it is not the free, solvated radical cation that reacts with water but the ion pair [radical cation–SO42−].
水溶液中的苯甲醇与光化学和辐射化学产生的˙OH和SO4˙−自由基以扩散控制速率反应,分别生成OH加合物和苯甲醇阳离子自由基。前者可以通过H+诱导(异裂)脱羟基化转化为阳离子自由基,而后者则通过a) 与水的亲电子反应(= 脱羟基化反应的逆过程)产生C核−OH加合物,以及b) 侧链C−H质子消除生成α-羟基苄基型自由基而衰变。然而,如果苯甲醇的阳离子自由基是通过双光子电离产生的,则C核−OH键的形成和侧链C−H键的断裂模式与SO4˙−反应时不同。由此可见,至少在这个反应中,与水反应的不是自由的溶剂化阳离子自由基,而是离子对[阳离子自由基−SO42−]。