Hanson Peter, Hendrickx Ramon A A J, Smith John R Lindsay
Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.
Org Biomol Chem. 2008 Feb 21;6(4):745-61. doi: 10.1039/b714707d. Epub 2008 Jan 11.
Relative rate constants have been measured for the oxidation of aryl methyl sulfides and sulfoxides by dimethyldioxirane in acetone, in mixtures of acetone with aprotic co-solvents of both higher and lower relative permittivity, and in aqueous acetone mixtures. Correlation analyses of the effects of substituents in the different solvents show that, with one exception, reactions take place via a single step mechanism in which the formation of the new SO bond and the elimination of acetone occur concertedly. The exception was oxidation of the sulfides in aqueous acetone containing the highest proportion of water of those studied (20% v/v). Here, the behaviour of the reaction is consistent with a two-step mechanism in which the oxidant reversibly attacks the sulfide to form an open-chain sulfonium betaine that subsequently fragments to sulfoxide and acetone. There is no evidence for the participation of an intermediate dioxathietane as has been found in the case of sulfide oxidations by (trifluoromethyl)methyldioxirane in CH(2)Cl(2) and similar aprotic solvents. It is not justified to generalise a mechanism involving a betaine, with or without a derived dioxathietane, to the reactions of dimethyldioxirane in acetone.
已测定了二甲基二氧杂环丙烷在丙酮、丙酮与相对介电常数较高和较低的非质子共溶剂的混合物以及丙酮 - 水混合物中氧化芳基甲基硫醚和亚砜的相对速率常数。对不同溶剂中取代基效应的相关分析表明，除了一个例外，反应通过单步机制进行，其中新的S - O键的形成和丙酮的消除协同发生。例外情况是在所研究的含最高比例水（20% v/v）的丙酮 - 水混合物中硫醚的氧化。在这里，反应行为符合两步机制，其中氧化剂可逆地攻击硫醚形成开链锍甜菜碱，随后分解为亚砜和丙酮。没有证据表明存在中间体二氧杂环丁烷参与反应，而在二氯甲烷和类似非质子溶剂中，（三氟甲基）甲基二氧杂环丙烷氧化硫醚的情况中已发现有中间体二氧杂环丁烷参与。将涉及甜菜碱（有或没有衍生的二氧杂环丁烷）的机制推广到二甲基二氧杂环丙烷在丙酮中的反应是不合理的。
