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Elsevier, Electrochimica Acta, 12(46), p. 1899-1903

DOI: 10.1016/s0013-4686(01)00429-7

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Tetraarylporphyrin synthesis by electrochemical oxidation of porphyrinogens

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Abstract

The electrochemical synthesis of tetraarylporphyrins has been reinvestigated. Whereas the direct electrolysis of a mixture of benzaldehyde and pyrrole gave only a 1% yield of tetraphenylporphyrin (A. Stanienda, Z. Naturforschg. 22b (1967) 1107), the electrochemical oxidation for 2 h of preformed porphyrinogens, obtained under the Lindsey conditions, can be successfully performed using catalytic amount of quinone as mediator. Furthermore, when condensation involves 3,4-difluoropyrrole, the electrolysis, at 1.2–1.45 V versus ECS, can be realized without any mediator, owing to the good electrochemical stability of the compound. The porphyrins yields (21–41%) depend on the nature of the aldehyde (benzaldehyde, pentafluorobenzaldehyde) and of the pyrrole (pyrrole, 3-fluoropyrrole, 3,4-difluoropyrrole). They are slightly smaller in the case of a redox catalysis and a little larger for the direct electrolysis. An improvement of the purification step was obtained by decreasing the quantity of quinone and performing the chromatography of the dication porphyrins.