Department of Organic Chemistry, Weizmann Institute of Science, Rehovot, Israel 76100.
J Am Chem Soc. 2015 May 13;137(18):5916-22. doi: 10.1021/jacs.5b01745. Epub 2015 May 1.
The synthesis of benzaldehyde derivatives by oxygenation of methylarenes is of significant conceptual and practical interest because these compounds are important chemical intermediates whose synthesis is still carried out by nonsustainable methods with very low atom economy and formation of copious amounts of waste. Now an oxygenation reaction with a 100% theoretical atom economy using a polyoxometalate oxygen donor has been found. The product yield is typically above 95% with no "overoxidation" to benzoic acids; H2 is released by electrolysis, enabling additional reaction cycles. An electrocatalytic cycle is also feasible. This reaction is possible through the use of an aqueous sulfuric acid solvent, in an aqueous biphasic reaction mode that also allows simple catalyst recycling and recovery. The solvent plays a key role in the reaction mechanism by protonating the polyoxometalate thereby enabling the activation of the methylarenes by an electron transfer process. After additional proton transfer and oxygen transfer steps, benzylic alcohols are formed that further react by an electron transfer-proton transfer sequence forming benzaldehyde derivatives.
通过甲芳烃的氧化来合成苯甲醛衍生物具有重要的概念和实际意义，因为这些化合物是重要的化学中间体，其合成仍然采用非可持续的方法，原子经济性非常低，并且会产生大量的废物。现在已经发现了一种使用多金属氧酸盐氧供体进行的具有 100%理论原子经济性的氧化反应。该反应的产率通常高于 95%，不会发生“过度氧化”生成苯甲酸；通过电解释放出氢气，从而可以进行额外的反应循环。电催化循环也是可行的。该反应可以在硫酸水溶液中进行，采用两相水反应模式，这也允许简单地回收和再循环催化剂。溶剂在反应机制中起着关键作用，通过质子化多金属氧酸盐来实现，从而可以通过电子转移过程激活甲芳烃。在进行额外的质子转移和氧转移步骤后，形成苄醇，它们通过电子转移-质子转移序列进一步反应形成苯甲醛衍生物。
