Electrocatalytic Nuclear Hydrogenation of Benzoic Acids in a Proton Exchange Membrane Reactor

Abstract

The nuclear hydrogenation of aromatic substrates to obtain saturated cyclic compounds is of great importance in the field of chemical and pharmaceutical industry, due to its readily obtained feedstocks, environmentally friendly and straightforward routes.1 For instance, the chemoselective hydrogenation of benzoic acids to cyclohexanecarboxylic acids has attracted great attention, as the hydrogenated products cyclohexanecarboxylic acids are important organic intermediates for pharmaceuticals, such as praziquantel, caprolactam, and ansatrienin.Several efficient catalysts based on monometallic Pd, Pt, Rh, and Ru and several alloys have been explored for the aromatic nuclear hydrogenation of benzoic acid and its derivatives.2 However, most of the catalytic reactions were performed under a high pressure of hydrogen gas, which leads to safety concerns. Therefore, the development of hydrogenation of benzoic acids to cyclohexanecarboxylic acids under mild conditions is still a challenging target.Under these backgrounds, we have demonstrated electrocatalytic nuclear hydrogenation in a proton exchange membrane (PEM) reactor (Figure 1). This system has several merits such as easy separation and recycle use of catalysts, operation under mild and benign conditions.3 We found that the use of PEM reactor with PtRu catalyst gave the corresponding cyclohexanecarboxylic acids with excellent current efficiencies in our demonstrations.AcknowledgementThe authors gratefully acknowledge supports by a CREST (JST Grant No.: JP65R1204400), Japan.References L. Zhang, J. Dong, X. L. Qiao, J. R. Qin, H. F. Sun, A. Q. Wang, L. B. Niu, G. Y. Bai, J. Catal., 372, 258–265 (2019).D. Dwivedi, R. K. Rai, K. Gupta, S. K. Singh, ChemCatChem, 9, 1930 – 1938 (2017).Fukazawa, J. Minoshima, K. Tanaka,Y. Hashimoto, Y. Kobori, Y. Sato, M. Atobe, ACS Sustain. Chem. Eng., 7, 11050-11055 (2019). Figure 1