Cobalt(II) porphyrazine catalysed reduction of nitrite

Studies on the catalytic reduction of nitrite on carbon electrodes modified with Co(II) tetra-2,3-pyridinoporphyrazine (CoTppa, 1), N,N',N ",N'''-tetr amethyltetra-2,3-pyridinoporphyrazine ([CoTm-2,3-tppa](4+), 2) and Co(II) N ,N',N ",N'''-tetramethyltetra-3,4-pyridinoporphyrazine ([CoTm-3,4-tppa](4+) , 3) are reported. There is a close correspondence between the proximity of the methyl groups to the porphyrazine ring and the catalytic activity of t he porphyrazine complexes. Bulk electrolysis gave ammonia and hydroxylamine as some of the products. The catalytic activity of the cationic complex, 3 , towards the detection of low concentrations of nitrite (<10(-9) M) in wat er containing sodium sulfate, was compared with the activities of the anion ic cobalt(II) tetrasulfophthalocyanine ([CoTSPc](4-), 4) and the mixed [(Co Tm)-Tm-II-3,4-tppa](4+).[CoTSPc](4-) (5) complexes. Complex 5 showed the be st catalytic activity of the three in that large currents were obtained for very low concentrations of nitrite. (C) 1999 Elsevier Science S.A. All rig hts reserved.