Photo-oxidative dealkylation of α-alkylbenzyl methyl ethers induced by titanium dioxide in acetonitrile
作者:Marta Bettoni、Tiziana Del Giacco、Cesare Rol、Giovanni V. Sebastiani
DOI:10.1002/poc.991
日期:2006.1
heterogeneity, the E/C ratio data were compared with those obtained from an electron-transfer photosensitised [by 9,10-dicyanoanthracene (DCA)] oxidation in a homogeneous phase. A significant confirmation of the mechanism, in both deaerated and aerated media, was obtained by the reaction performed from 4-methoxy-α-ethylbenzyl methyl ether (as a model) in the presence of H218O, sensitised by either TiO2
在脱气的CH 3 CN中进行TiO 2敏化的α-烷基苄基甲基醚的光氧化反应,得到了预期的相应酮,而在充气介质中,相对于酮,以脱烷基化化合物(苯甲酸甲酯)为主要产物,或独家产品(当烷基为叔丁基时)。产物分析和分布以及相对反应性的定性估计表明,脱气CH 3中的机理CN与先前对非α-烷基化的苄基醚所假设的相同;特别地,羰基化合物应通过将苄基(通过阳离子的去质子化获得)氧化成相应的阳离子而形成。为了证明在充气介质中形成苯甲酸甲酯是合理的假设,即α-烷基-α-甲氧基苄基过氧自由基(由氧竞争性地攻击苄基获得)经历了脱烷基过程;特别地,该中间体作为叔过氧自由基可以形成二聚体,该二聚体演变成相应的氧自由基,从而通过β-断裂过程得到酯。通过评估酯/羰基(E / C)摩尔比与苄基自由基中间体的绝热电离电势之间的关系,可以证实在充气介质中提出的一般机理。为了评估介质异质性的影响,将E / C比数据与通过均相中的电子转移光敏[通过9