The presented work is dealing with electrochemical reduction of three isomeric benzene dialdehydes: orthophthalaldehyde (benzene-1,2-dicarboxaldehyde, OPA), isophthalaldehyde (benzene-1,3-dicarboxaldehyde, IPA) and terephthalaldehyde (benzene-1,4-dicarboxaldehyde, TPA) in aprotic media. Whereas their electrochemical reduction in aqueous buffered solutions is described and compared in the literature (together with their covalent hydration) [1-3], the reduction mechanism of the title compounds in non-aqueous and aprotic solvents has not been investigated up to now (with one exemption:  OPA and TPA in methanol [4]).

The reduction was investigated by voltammetric methods, electrolyses, coulometry, UV-vis and EPR spectra in order to identify the primary radical intermediates as well as reduction products. OPA and TPA form stable radical anions after the first ET which were confirmed by the in-situ EPR spectroelectrochemical experiments. Using cyclic voltammetry the influence of the water content in dimethylformamide on the stability of radicals was followed. The first electroreduction step of IPA was irreversible, therefore the EPR spectra did not reveal any paramagnetic species. The differences were discussed and correlated with quantum chemical calculations.

Acknowledgement: The material support from the grant GACR No. 13-21704S and the institutional support RVO 61388955 are acknowledged.

[1] M. S. Baymak, E. Kulla and P. Zuman, J. Mol. Liq., 2007, 131-132, 24_28.

[2] M. S. Baymak, W. J. Bover, H. Celik and P. Zuman, Electrochim. Acta, 2005, 50, 1347_1359.

[3] M. S. Baymak, K. L. Vercoe and P. Zuman, J. Phys. Chem. B, 2005, 109, 21928_21929.

[4] D. Jannakoudakis and G. Kokkinidis, Chim. Chron., 1977, 6, 439_450.