A promising electro-oxidation of methyl-substituted aromatic compounds to aldehydes in aqueous imidazole ionic liquid solutions

• Electro-oxidation of methyl-substituted aromatics in ionic liquids is described.
• The process is sensitive to the acid strength of the IL solutions.
• The chemistry was monitored using in-situ FTIR.
• Excellent electrochemical stability of the ILs was demonstrated.
• The method represents a promising way to prepare aromatic aldehydes.

In this paper we describe the electro-oxidation of methyl-substituted aromatic compounds to the corresponding aldehydes in aqueous imidazole ionic liquid (IL) solutions and using a platinum electrode. The electro-oxidative behavior of p-methoxy toluene (p-MT) was studied in the ILs using cyclic voltammetry (CV), and the oxidation was shown to be an irreversible process. Increasing the acid strength of the ILs led to further oxidation to the corresponding acid. The controlled potential electrolysis of methyl-substituted aromatic compounds was also investigated under the optimized reaction conditions and the products were detected by NMR, IR and gas chromatography/mass spectrometry (GC/MS). The method represents a promising way to prepare aromatic aldehydes. In order to detect intermediates, in-situ Fourier transform infrared spectroscopy (in-situ FTIR) data was acquired during the oxidation processes. The results further confirmed that the procedure provides a selective approach to the synthesis of aromatic aldehydes. The selectivity toward formation of the corresponding aromatic aldehydes was 21–92% when using the optimized reaction conditions. Excellent electrochemical stability of the ILs was demonstrated and they could be recycled at least 35 times.