resumo
A novel type of supported copper(II) catalyst was prepared by the treatment of a Zn-Al layered double hydroxide containing 2,2'-bipyridine-5,5'-dicarboxylate (BDC) anions with a solution of CuCl(2) in ethanol. The Cu loading in the recovered material, designated as LDH-BDC/Cu, was ca. 4%, with an approximate BDC:Cu:Cl molar ratio of 2:1:1. The catalytic performance of LDH-BDC/Cu was examined in the liquid-phase oxidation of styrene, ethylbenzene, cyclohexane and cyclooctane at room temperature, using acetonitrile/water as solvent, and hydrogen peroxide (30%) or tert-butyl hydroperoxide (70%) as terminal oxidant. The main products were benzaldehyde from styrene (up to 14% yield at 24 h). acetophenone from ethylbenzene (up to 8% yield at 24 h), and a mixture of cyclohexanol and cyclohexanone from cyclohexane (up to 5% yield at 24 h). For styrene oxidation using H(2)O(2), benzaldehyde was the only observed reaction product (6-11% yield at 24 h), whereas the same reaction carried out in homogeneous phase using the complex [Cu(bipy)Cl(2)] (bipy = 2,2'-bipyridine) gave the by products 2-hydroxy-acetophenone (HAP) and benzoic acid (BAc) in addition to the main product benzaldehyde (60-90% selectivity, 9-11% yield at 24 h). When t-BuOOH was used as the oxidant for styrene oxidation in the presence of LDH-BDC/Cu, the by products HAP, BAc and acetophenone (each with yields of 1-9% at 24 h) were formed in addition to benzaldehyde (5-14% yield at 24 h). Recycling tests for the latter system showed that the solid LDH-BDC/Cu could be recovered at the end of a catalytic run and used in a second run. For the oxidation of styrene and ethylbenzene using H(2)O(2) or t-BuOOH as oxidants, titration experiments showed that LDH-BDC/Cu was significantly more efficient than [Cu(bipy)Cl(2)] in terms of the "productive" consumption of the oxidant. (C) 2009 Elsevier B.V. All rights reserved.
palavras-chave
CU(II) COMPLEXES; 2,2'-BIPYRIDINE LIGANDS; COORDINATION-COMPOUNDS; SELECTIVE OXIDATION; BUTYL HYDROPEROXIDE; MAGNETIC-PROPERTIES; METAL-HYDROXIDES; CYCLOHEXANE; ALCOHOLS; CRYSTAL
categoria
Chemistry
autores
Monteiro, B; Gago, S; Balula, SS; Valente, AA; Goncalves, IS; Pillinger, M
nossos autores
Anabela Tavares Aguiar Valente
Investigador Principal
Isabel Maria de Sousa Gonçalves
Professor associado
Martyn Pillinger
Investigador Principalagradecimentos
The authors are grateful to the FCT, OE and FEDER for financial support provided through the project with reference POCI/CTM/58507/2004. B.M. (Ph.D. grant), S.G. and S.S.B. (postdoctoral grants) thank the FCT for research grants.