Behavior of Ketyl radical in the micelle solution in the presence of silver ion or silver particle

"光-丙酮法"是制备精细分散的胶体金属（Ag、Au、Pt和Cu）的一种易操作的方法。在这项研究中，芳香酮被用来代替丙酮，以研究在反应过程中的酮自由基的作用。在十二烷基硫酸钠（SDS）胶束和芳香酮（如二苯甲酮和苯乙酮）存在下，过胆酸银水溶液在近紫外光下发生光解。细分散的胶体银的形成和芳香酮的光漂白是由近紫外光照射引起的，其仅被芳香酮吸收（敏化光还原）。银离子的敏化光还原和芳香酮的光漂白的总体特征被解释在一个简单的反应方案，需要适当的动力学参数的组合。也就是说，通过近紫外光激发芳香酮产生芳香酮三重态，其从SDS胶束中夺取H原子，产生酮基自由基。部分酮自由基还原银离子和银离子团簇并返回芳酮。其它的酮基自由基则转化为相应的频哪醇、羟基和与SDS的偶联物等副产物。注意到由于颗粒的尺寸效应，在早期阶段形成的胶体银的消光系数小于通常值。用激光光解法证实了反应混合物中二苯甲酮酮自由基的存在，并比较了不同反应条件下自由基的寿命。利用光-丙酮法独特的反应过程，成功制备出了结构和光谱性质均不同于合金胶体的复合贵金属胶体。

"Photo-acetone method" has been known as a tractable method to prepare finely dispersed colloidal metals (Ag, Au, Pt and Cu). In this study, aromatic ketone was used instead of acetone in order to investigate the role of the ketyl radical during the reaction. Aqueous silver percholate solutions were photolyzed with near-UV light in the presence of sodium dodecylsulfate (SDS) micelle and aromatic ketone, such as benzophenone and acetophenone. The formation of finely dispersed colloidal silver and the photobleach of aromatic ketone were caused by irradiation with near-UV light, which was absorbed solely by aromatic ketone (sensitized photoreduction). Gross features of the sensitized photoreduction of silver ion and the photobleach of aromatic ketone were interpreted in term of a simple reaction scheme entailing suitable combinations of the kinetics parameters. Namely, the excitation of aromatic ketone by near-UV light yields an aromatic ketone triplet, which abstracts an H atom from SDS micelle, giving rise to a ketyl radical. Some ketyl radical reduces silver ion and silver ion cluster and goes back to aromatic ketone. Other ketyl radical changes into certain byproducts such as the corresponding pinacol, hydrol and coupling compound with SDS.It was noticed that an extinction coefficient of colloidal silver formed during the early stage was smaller than the usual value because of the size effect of the particles. The existence of the ketyl radical of benzophenone in the reaction mixture was confirmed by laser photolvsis, It was tried to compare the lifetime of the ketyl radical under various reaction conditions. Taking advantage of the unique reaction process of the photo-acetone method, the composite noble metal colloid, whose structure and spectroscopic properties were different from alloy colloid, has been successfully prepared.