Oxidação de cicloexano pelo sistema GIF : sobre-oxidação e influencia dos ligantes

AUTOR(ES)
DATA DE PUBLICAÇÃO

1991

RESUMO

In earlier research, it had not been possible to close the mass balance for cyclohexane oxidation by the Gif system. lnitially we quantified the losses of cyclohexane by evaporation and were able to improve the mass balances to 97,2% at 20°C and to 99,6% a 80°C. ln order to explain the remaining differences we looked for possible overoxidation and/or coupling products. We accumulated the products in the cyclohexane oxidation and studied the oxidation of cyclohexanone and cyclohexanol under Gif conditions. ln the accumulative cyclohexane oxidation we observed the formation of cyclohexylpyridines and bipyridines and of a small quantity of 1,4-cyclohexanedione. Carboxylic acids were not formed. The quantity of cyclohexylpyridines formed at 20°C was estimated as 3%, which allowed closing the mass balance of the cyclohexane oxidation. At 80°C deactivation of the catalytically active species was observed. Overoxidation and coupling products were only formed in very small quantities, which confirmed the mass balance of 99,6%. Cyclohexanone and cyclohexanol, added in quantities comparable to those obtained in the cyclohexane oxidation, were oxidized with smaller turnover frequencies. The principal product observed in the cyclohexanone oxidation was 1,4-cyclohexanedione, which was only obtained with 10% selectivity. ln the cyclohexanol oxidation, cyclohexanone and hydroxycyclohexanone were formed with 30% and 10% selectivity, respectively. Coupling products between cyclohexanone or cyclohexanol and pyridine were only obtained in very small quantities. However it was not possible to close the mass balances of the cyclohexanone and cyclohexanol oxidation reactions. The effect of twelve substituted aromatic amines, in the proportion ligand:iron of 5:1, was studied in the cyclohexane oxidation by the Gif system. ln general the effect of the different ligands on the turnover frequency and the selectivity was very small. At 20°C an increase of the proportion 2,2 -bypiridine:iron to 20:1 slightly improved the results. With a larger quantity of the ligand (100:1) the selectivity was strongly reduced. With the use of an even larger quantity (850:1), the catalyst Iost its activlty. At 80°C the effect of the ligand was even smaller. Based on the m-oxodiiron structure of the methane monooxygenase enzyme and on the proposals of Barton et al., a mechanism is presented which explains the results obtained.

ASSUNTO(S)

quimica organica agentes de oxidação

ACESSO AO ARTIGO

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