Oxidation of alcohols with tert-butylhydroperoxide catalyzed by Co(II) complexes immobilized between silicate layers of bentonite M.H. Peyrovi * , Vahid Mahdavi, M.A. Salehi, R. Mahmoodian Department of Chemistry, Shahid Beheshti University, Evin, Tehran 1983963113, Iran Received 30 January 2005; accepted 12 April 2005 Available online 2 June 2005 Abstract The oxidation of alcohols with tert-butylhydroperoxide (TBHP), in the presence of immobilized Co 2+ complexes with ligands of 2,2 0 -bipyridine (bpy), ethylenediamine (en), acetylacetonate (acac), urea, N,N 0 -ethylenebis(salicylideneamine) (salen), N,N 0 -propyl- enebis(salicylideneamine) (salpn) and N,N 0 -phenylenebis(salicylideneamine) (salophen) were investigated. It was found that immo- bilized [Co(bpy) 2 ] 2+ /bentonite is an efficient catalyst for the oxidation of alcohols such as cyclohexanol (91% conversion; 100% selectivity), benzyl alcohol (53% conversion; 100% selectivity) and hexanol (40% conversion; 100% selectivity). Effect of reaction time, effect of the amount of Co 2+ in catalyst and the effect of type of substrates and oxidants in this catalysis systems were inves- tigated. In the best conditions, TBHP is more efficient oxidant with respect to H 2 O 2 and order has been observed for the percentage of conversions of alcohols: 2° > benzylic > 1°. Ó 2005 Elsevier B.V. All rights reserved. Keywords: Co(II) complexes; Bentonite; Cyclohexanol; Oxidation of alcohols 1. Introduction The search for new oxidation catalysts is one of the most important topics connected with both industrial and academic research. Oxidation is also one of the most important reactions for the metabolism of biotic sub- strates and many enzymes are known to catalyze various type or oxidation [1]. The desire to mimic enzymatic sys- tem has prompted an extensive area of research into syn- thetic porphyrin, phetalocyanine, and Schiff base models of enzyme active sites, especially for monooxygenase en- zymes of the cytochrome P-450 family [2–5]. The oxida- tion of alcohols to aldehydes or ketones is a vital reaction in synthetic organic chemistry. In this way, chemists have used different kinds of metal salts and oxides in the form of homogeneous catalysts [6–10] or supported metal ions and supporting oxometal catalysts as heterogeneous sys- tems [11–15]. The complexes of transition metal ions encapsulated in zeolite cages or immobilized between sil- icate layers of bentonite (Scheme 1) show remarkable high activity and selectivity toward oxidation of hydro- carbons in liquid phase [16]. In previous studies, sup- ported complexes of Zn +2 , Cu +2 , Ni +2 ions have been applied in oxidation reactions [17]. In this paper, the catalytic effect of some Schiff base and bidentate Co(II) complexes are investigated for oxi- dation of alcohols in the heterogeneous systems. 2. Experimental 2.1. Materials All materials were of commercial reagent grade. Sal- icylaldehyde, p-phenylene diamine and the ligands 1566-7367/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2005.04.010 * Corresponding author. Tel./fax: +98 21 2401765. E-mail address: M-Peyrovi@cc.sbu.ac.ir (M.H. Peyrovi). www.elsevier.com/locate/catcom Catalysis Communications 6 (2005) 476–479