Stergiou Athanasios D, Broadhurst Daniel H, Symes Mark D
WestCHEM, School of Chemistry, University of Glasgow, University Avenue, GlasgowG12 8QQ, U.K.
ACS Org Inorg Au. 2022 Nov 21;3(1):51-58. doi: 10.1021/acsorginorgau.2c00047. eCollection 2023 Feb 1.
Anilines and substituted anilines are used on the multi-ton scale for producing polymers, pharmaceuticals, dyes, and other important compounds. Typically, these anilines are produced from their corresponding nitrobenzene precursors by reaction with hydrogen at high temperatures. However, this route suffers from a number of drawbacks, including the requirement to handle hydrogen gas, rather harsh reaction conditions that lead to a lack of selectivity and/or toleration of certain functional groups, and questionable environmental sustainability. In light of this, routes to the reduction of nitrobenzenes to their aniline derivatives that operate at room temperature, in aqueous solvent, and without the requirement to use harsh process conditions, hydrogen gas, or sacrificial reagents could be of tremendous benefit. Herein, we report on a highly selective electrocatalytic route for the reduction of nitrobenzenes to their corresponding anilines that works in aqueous solution at room temperature and which does not require the use of hydrogen gas or sacrificial reagents. The method uses a polyoxometalate redox mediator, which reversibly accepts electrons from the cathode and reacts with the nitrobenzenes in solution to reduce them to the corresponding anilines. A variety of substituted nitroarenes are explored as substrates, including those with potentially competing reducible groups and substrates that are difficult to reduce selectively by other means. In all cases, the selectivity for the redox-mediated route is higher than that for the direct reduction of the nitroarene substrates at the electrode, suggesting that redox-mediated electrochemical nitroarene reduction is a promising avenue for the more sustainable synthesis of substituted anilines.
苯胺和取代苯胺以多吨规模用于生产聚合物、药物、染料及其他重要化合物。通常，这些苯胺是通过其相应的硝基苯前体在高温下与氢气反应制得。然而，该路线存在诸多缺点，包括需要处理氢气、反应条件相当苛刻导致缺乏选择性和/或对某些官能团的耐受性，以及环境可持续性存疑。有鉴于此，在室温下于水性溶剂中操作且无需使用苛刻工艺条件、氢气或牺牲试剂的将硝基苯还原为其苯胺衍生物的路线可能具有巨大优势。在此，我们报道了一种高度选择性的电催化路线，用于将硝基苯还原为其相应的苯胺，该路线在室温下的水溶液中起作用，且无需使用氢气或牺牲试剂。该方法使用多金属氧酸盐氧化还原介质，其可逆地从阴极接受电子并与溶液中的硝基苯反应将其还原为相应的苯胺。研究了多种取代硝基芳烃作为底物，包括那些具有潜在竞争性可还原基团的底物以及难以通过其他方法选择性还原的底物。在所有情况下，氧化还原介导路线的选择性高于电极上硝基芳烃底物的直接还原选择性，这表明氧化还原介导的电化学硝基芳烃还原是更可持续地合成取代苯胺的一条有前景的途径。
