Tetraarylporphyrin synthesis by electrochemical oxidation of porphyrinogens

The electrochemical synthesis of tetraarylporphyrins has been reinvestigate d. Whereas the direct electrolysis of a mixture of benzaldehyde and pyrrole gave only a 1% yield of tetraphenylporphyrin (A. Stanienda, Z. Naturforsch g. 22b (1967) 1107), the electrochemical oxidation for 2 h of preformed por phyrinogens, obtained under the Lindsey conditions, can be successfully per formed using catalytic amount of quinone as mediator. Furthermore, when con densation involves 3,4-difluoropyrrole, the electrolysis. at 1.2-1.45 V ver sus ECS, can be realized without any mediator, owing to the good electroche mical stability of the compound. The porphyrins yields (21-41%) depend on t he nature of the aldehyde (benzaldehyde, pentafluorobenzaldehyde) and of th e pyrrole (pyrrole, 3-fluoropyrrole. 3,4-difluoropyrrole). They are slightl y smaller in the case of a redox catalysis and a little larger for the dire ct electrolysis. An improvement of the purification step was obtained by de creasing the quantity of quinone and performing the chromatography of the d ication porphyrins. (C) 2001 Elsevier Science Ltd. All rights reserved.