A study of poly(4-vinylpyridine)-supported ruthenate in the oxidation of alcohols Holger B. Friedrich* and Nirad Singh School of Chemistry, Howard College, University of KwaZulu-Natal, Durban 4041, South Africa Received 20 April 2006; accepted 20 May 2006 Sodium ruthenate was supported on 2% and 25% cross-linked poly(4-vinylpyridine). These compounds were found to be efficient and selective catalysts for the room temperature oxidation of internal and external alcohols to aldehydes and ketones, respectively. The catalysts were active with a wide range of co-oxidants and no over-oxidation products were observed. KEY WORDS: alcohols; oxidation; polymer-supported; ruthenium. 1. Introduction The selective oxidation of alcohols to carbonyl com- pounds is an important transformation in synthetic organic chemistry, as it is essential for the preparation of many key synthetic intermediates [1–4]. Traditionally such transformations have been performed with inor- ganic oxidants, e.g., chromium(VI) compounds in stoi- chiometric quantities [5,6]. However, the toxic and corrosive nature of these compounds has limited their use. Whilst a number of effective homogeneous systems are known, [1,6] issues such as product separation from the catalyst and catalyst recovery remain problematic. It is usually desirable to replace stoichiometric reagents with catalysts and to facilitate the efficient recovery of the catalyst from the reaction products thereby reducing inorganic waste [7,8]. The study of polymer-supported catalysts and reagents is motivated by the major advantage of the physical separation of the supported reagent from the substrates and products, thereby allowing the recycling of expensive catalysts (e.g., noble metals) or of toxic products and is of prime economic and environmental importance [9,10]. Poly(4-vinylpyridine) (P4VP) and poly(2-vinylpyridine) have been used as supports for chromium peroxide and these stoichiometric oxidants have been reported to be efficient for the oxidation of various benzylic and allylic alcohols [11]. The stoichi- ometric oxidants poly(4-vinylpyridinium dichromate) and poly(4-vinylpyridinium chlorochromate) have also been reported, with the former being commercially available [12]. A major disadvantage of the above sys- tems is that only the polymeric backbone can be recycled and not the supported chromium peroxide and dichro- mate species. Following our observation that Os(VI) oxides can be supported on poly(4-vinylpyridine) and that these sup- ported oxides are effective dihydroxylation catalysts [13], we concluded that the chemistry of ruthenate on P4VP may be worth investigating. Unsupported ruthe- nate is a well-known, but not very selective, oxidant of alcohols [14,15]. Poly(vinylpyridine) is a microporous resin which posses high flexibility and readily swells in solvents, increasing accessibility to active sites. To our knowledge, prior to our work, there has been no reported literature of any P4VP-supported ruthenium compounds for the oxidation of alcohols [16]. However, [RuCl 2 (CO) 3 ] 3 supported on P4VP for olefin hydroge- nation has been reported [17], as has been perruthenate supported on Amberlyst anion exchange resin [18]. We now report on a study of ruthenate supported on cross- linked P4VP in a series of catalytic alcohol to carbonyl oxidation reactions. 2. Results and discussion 2.1. Catalyst characterisation Sodium ruthenate was prepared by the reduction of ruthenium tetroxide with NaOH. The ruthenate was loaded on the polymer, poly(4-vinylpyridine) cross- linked with 2% divinyl benzene, following an incipient wet impregnation technique. Both 1% and 2% ruthe- nium loaded (by weight) polymers were prepared. A ruthenate loaded P4VP compound cross-linked with 25% divinyl benzene was also prepared. Flame emission spectroscopy showed that this latter compound was 0.5% ruthenium loaded, and the expected 2% loading could thus not be achieved. X-ray photoelectron *To whom correspondence should be addressed. E-mail: friedric@ukzn.ac.za Catalysis Letters Vol. 110, Nos. 1–2, August 2006 (Ó 2006) 61 DOI: 10.1007/s10562-006-0099-6 1011-372X/06/0800–0061/0 Ó 2006 Springer Science+Business Media, Inc.