Efficient Selective Oxidation of Cyclohexane Catalyzed by Metallodeuteroporphyrins with Air in the Presence of l -Cystei
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Efficient Selective Oxidation of Cyclohexane Catalyzed by Metallodeuteroporphyrins with Air in the Presence of L-Cysteine Weiyou Zhou • Bingcheng Hu • Chengguo Sun Shichao Xu • Zuliang Liu
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Received: 31 May 2011 / Accepted: 28 August 2011 / Published online: 21 September 2011 Ó Springer Science+Business Media, LLC 2011
Abstract Efficient selective oxidation of cyclohexane to cyclohexanol and cyclohexanone catalyzed by metallodeuteroporphyrins with L-cysteine as the cocatalyst has been investigated. Apparently high catalytic activities of metallodeuteroporphyrins and selectivities of cyclohexanone were observed. The results could be attributed to the dual roles of L-cysteine as the axial ligand and the dehydrogenized reagent in the catalytic oxidation. Keywords L-Cysteine
Deuteroporphyrins Cyclohexane oxidation Cocatalyst
1 Introduction The development of efficient catalysts for selective oxidation of unactivated C–H bonds of hydrocarbons has attracted significant attention from organic and industrial chemists. Simulation of the function of cytochrome P-450 with transition metal complexes has led to the discovery of metalloporphyrins-catalyzed oxidation of hydrocarbons with various oxygen donors such as iodosylbenzene (PhIO) [1, 2], ROOH [3, 4], pyridine N-oxide [5], KHSO5 [6] and hydrogen peroxide [7, 8]. From the view of potential
W. Zhou (&) School of Petrochemical Engineering, Changzhou University, Changzhou 213164, China e-mail: [email protected] B. Hu C. Sun S. Xu Z. Liu College of Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China e-mail: [email protected]
practical use of the metalloporphyrin-based systems for oxidation, the research emphasis should be directed to the use of cheap, easily accessible and environmentally friendly oxidants such as molecular oxygen. Using air as the oxidant, the catalytic activities of some metalloporphyrin derivatives including metallodeuteroporphyrin dimethyl esters [M(DPDME)] in the oxidation of cyclohexane have been investigated in our previous work [9]. All these complexes could smoothly catalyze the oxidation of cyclohexane and M(DPDME) exhibited the highest catalytic activity. Subsequently, we set out to investigate the M(DPDME)catalyzed oxidation of cyclohexane with air in presence of additive reagents. Introduction of cocatalysts is a potential method to improve the catalytic activity of metalloporphyrin-based systems and various cocatalysts have been studied. According to their functions, the first kind are coreductant such as aldehyde [10, 11], anthracene [12], NaBH4 [13] and carbon monoxide [14], which could evidently increase the catalytic activities and milden the reaction conditions. However, these additives will be consumed and converted to byproducts, which consequentially increases the cost and makes the purification difficult. The other kind of cocatalysts is axial ligand such as imidazole [15, 16], pyridine [17] and ammonium acetate [18], which can facilitate the formation of high-valent oxometal s
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