Study on electrochemical reduction mechanism of p-nitrophenylacetic acid prepared by electrocarboxylation

The direct carboxylation of organic halides under CO 2 atmosphere by electrochemical reduction is an effective way to realize the value utilization of waste (CO 2 ), and has great potential in green organic synthesis. P-nitrophenylacetic acid is a chemical raw material in great demand, which can be used not only in medicine and other organic synthesis intermediates but also in biochemical research. In this paper, the electrochemical reduction mechanism of p-nitrobenzyl bromide (PNBB) in N 2 and CO 2 atmosphere was investigated by cyclic voltammetry (CV), in-situ FT-IR spectroelectrochemistry, and bulk electrolysis experiments. Under N 2 conditions, the electrochemical behavior of PNBB in aprotic acetonitrile solvent is a 1-electron irreversible transfer process. However, in the presence of CO 2 , it is a completely irreversible 2-electron transfer process. The electrolytic products were analyzed by 1 H NMR, 13 C NMR and MS. The results showed that the electrolytic products were 1,2-bis(4-nitrophenyl) ethane and p-nitrophenylacetic acid under N 2 and CO 2 conditions, respectively. The successful preparation of p-nitrophenylacetic acid provides more possibilities for the “green” synthesis of helpful chemical products from organic halides.