Scorpionate complexes of vanadium(III or IV) as catalyst precursors for solvent-free cyclohexane oxidation with dioxygen

Mishra, Gopal S.; Silva, Telma F. S.; Martins, Luísa M. D. R. S.; Pombeiro, Armando J. L.

doi:10.1351/PAC-CON-08-10-08

Pure Appl. Chem., 2009, Vol. 81, No. 7, pp. 1217-1227

http://dx.doi.org/10.1351/PAC-CON-08-10-08

Published online 2009-05-29

Scorpionate complexes of vanadium(III or IV) as catalyst precursors for solvent-free cyclohexane oxidation with dioxygen

Gopal S. Mishra¹, Telma F. S. Silva^2,1, Luísa M. D. R. S. Martins^1,3 and Armando J. L. Pombeiro¹*

¹ Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, TU Lisbon, Av. Rovisco Pais, 1049-001, Lisbon, Portugal
² Área Científica de Física, ISEL, R. Conselheiro Emídio Navarro, 1959-007, Lisbon, Portugal
³ Departamento de Engenharia Química, ISEL, R. Conselheiro Emídio Navarro, 1959-007, Lisbon, Portugal

Abstract: The V-scorpionate vanadium complexes [VCl₃{HC(pz)₃}] (pz = pyrazolyl) and [VCl₃{SO₃C(pz)₃}] catalyze cyclohexane oxidation with dioxygen, to cyclohexanol (the main product) and cyclohexanone, under solvent-free conditions. [VCl₃{HC(pz)₃}] provides the best activity (13 % conversion into the ketone and alcohol, with high selectivity, at the O₂ pressure of 15 atm, at 140 ºC, 18 h reaction time). The reaction is further promoted (to 15 % conversion) by pyrazinecarboxylic acid (PCA). The use of C- or O-radical traps supports the involvement of a free-radical reaction mechanism. Several reaction parameters have been varied in a systematic study, directed toward optimization of the process.