Mechanistic investigation of the autooxidation of cumene catalyzed by transition metal salts supported on polymer

• Published in: Journal of molecular catalysis. A, Chemical Vol. 136; no. 1; pp. 1 - 11
• Main Authors: Hsu, Ying Fang, Cheng, Cheu Pyeng
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 11.11.1998; Elsevier
• Subjects: Catalysis; Catalytic reactions; Chemistry; Cumene; Exact sciences and technology; General and physical chemistry; Polymer; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Transition metal salt; Transition metal salt; Cumene; Polymer; Catalytic reaction; Temperature effect; Transition metal; NMR spectrometry; Selectivity; Experimental study; Inductive coupling plasma spectrometry; Supported catalyst; Heterogeneous catalysis; Acrylate polymer; Reaction mechanism; Oxidation; Kinetics
• ISSN: 1381-1169; 1873-314X
• DOI: 10.1016/S1381-1169(98)00016-8

The autooxidations of cumene to cumene hydroperoxide (CHP) in the presence of various transition metal salts supported on Bio-Rex 70 which is a macroreticular polyacrylate with carboxylate functional group, were investigated. The polymer supported catalyst is denoted as MS-BR- r in which MS represents transition metal salt, BR represents the polymer support and r is the loading of metal salt in the unit of mmoles per gram of dry support. In a catalyst loading of 0.20 g per 10 ml of cumene and initial O 2 pressure 103 kPa at 363 K, the catalyzed autooxidation rate follows the order: Mn(OAc) 2-BR-0.6>Co(OAc) 2-BR-0.6>FeCl 2-BR-0.6>Cu(OAc) 2-BR-0.6>Cr(NO 3) 3-BR-0.6≫Ni(OAc) 2-BR-0.6. The selectivities to CHP are 97% for Cu(OAc) 2-BR-0.6 and Cr(NO 3) 2-BR-0.6; and 92% for Mn(OAc) 2-BR-0.6, Co(OAc) 2-BR-0.6 and FeCl 2-BR-0.6. These data indicate that Cu(OAc) 2-BR-0.6 is the best catalysts among the catalysts investigated in this work. The metal loading effect was investigated for Co(OAc) 2-BR- r, r=0.3, 0.6, 1.5, 2.0 and 2.5. In the catalyst loading of 0.20 g per 10 ml of cumene and initial O 2 pressure 100 kPa at 363 K, the oxidation rate increases with r from 3.96×10 −5 M/s at r=0.3 to 8.35×10 −5 M/s for r=2.5. The selectivity to CHP decreases with increasing r from 93.8% for r=0.3 to 88.1% for r=2.5 at a conversion of 7%. When cumene autooxidation catalyzed by Co(OAc) 2-BR-2.0 was investigated at temperatures in the range of 363 K to 323 K, we found that oxidation rate decreases with temperature. However, unexpectedly, the selectivity decreases with temperature. This is interpreted by considering the competing reactions between the formation of CHP which has a high activation energy and the catalyzed redox decomposition of CHP which has a low activation energy. When temperature decreases, the rate of formation of CHP decreases more than that of the decomposition of CHP. When the autooxidation is catalyzed by a small amount of soluble copper(II) laurate or copper(II) stearate, the oxidation rate is faster and the selectivity to CHP is lower than that catalyzed by Cu(OAc) 2-BR-0.6 under similar reaction conditions. The carboxylate coordination environment on copper(II) reaction center is not sufficient for Cu(OAc) 2-BR-0.6 to be an effective catalyst in cumene autooxidation. We propose that the role played by the polymer support is that the backbone of the polymer reduces the rate of the catalyzed redox decomposition of CHP by hindering the change of the coordination environments on the copper center during the redox decomposition reaction of CHP.