Nguyen Ky, Nguyen Van, Tran Hieu, Pham Phong
Faculty of Chemistry, University of Science, Vietnam National University Hanoi Vietnam
RSC Adv. 2023 Mar 6;13(11):7168-7178. doi: 10.1039/d3ra00332a. eCollection 2023 Mar 1.
Oxidative C-H functionalization with O is a sustainable strategy to convert feedstock-like chemicals into valuable products. Nevertheless, eco-friendly O-utilizing chemical processes, which are scalable yet operationally simple, are challenging to develop. Here, we report our efforts, organo-photocatalysis, in devising such protocols for catalytic C-H bond oxidation of alcohols and alkylbenzenes to ketones using ambient air as the oxidant. The protocols employed tetrabutylammonium anthraquinone-2-sulfonate as the organic photocatalyst which is readily available from a scalable ion exchange of inexpensive salts and is easy to separate from neutral organic products. Cobalt(ii) acetylacetonate was found to be greatly instrumental to oxidation of alcohols and therefore was included as an additive in evaluating the alcohol scope. The protocols employed a nontoxic solvent, could accommodate a variety of functional groups, and were readily scaled to 500 mmol scale in a simple batch setting using round-bottom flasks and ambient air. A preliminary mechanistic study of C-H bond oxidation of alcohols supported the validity of one possible mechanistic pathway, nested in a more complex network of potential pathways, in which the anthraquinone form - the oxidized form - of the photocatalyst activates alcohols and the anthrahydroquinone form - the relevant reduced form of the photocatalyst - activates O. A detailed mechanism, which reflected such a pathway and was consistent with previously accepted mechanisms, was proposed to account for formation of ketones from aerobic C-H bond oxidation of both alcohols and alkylbenzenes.
利用氧气进行氧化C-H官能团化是一种将类似原料的化学品转化为有价值产品的可持续策略。然而，开发可扩展且操作简单的环保型氧气利用化学过程具有挑战性。在此，我们报告了我们在有机光催化方面的努力，旨在设计这样的方案，以环境空气为氧化剂，将醇类和烷基苯的C-H键催化氧化为酮。该方案使用四丁基铵蒽醌-2-磺酸盐作为有机光催化剂，它可通过廉价盐的可扩展离子交换轻松获得，并且易于与中性有机产物分离。发现乙酰丙酮钴（II）对醇的氧化有很大帮助，因此在评估醇的范围时作为添加剂包含在内。该方案使用无毒溶剂，可容纳多种官能团，并且在简单的分批设置中，使用圆底烧瓶和环境空气，很容易扩大到500 mmol规模。对醇的C-H键氧化的初步机理研究支持了一种可能的机理途径的有效性，该途径嵌套在一个更复杂的潜在途径网络中，其中光催化剂的蒽醌形式（氧化形式）活化醇，而蒽氢醌形式（光催化剂的相关还原形式）活化氧气。提出了一个详细的机理，该机理反映了这样的途径并且与先前接受的机理一致，以解释醇类和烷基苯的需氧C-H键氧化形成酮的过程。
