Selective oxidation of sulfides to sulfoxides or sulfones using keggin heteropolyacid as catalyst

G. ROMANELLI, P. VÁZQUEZ, P. TUNDO

Pekin, China

Conferencia; IUPAC- 16 International Conference on Organic Synthesis; 2005

Currently there is considerable interest in exploiting both the structure of catalyst precursors and the multicenter active sites to facilitate catalysis by polyoxometalates. It has been stressed that it is important to discover more reliable and efficient procedures before the exploration of possible new reactivity patterns. Thus, it is very important to use fully characterized and more reliable catalyst precursors for catalytic reactions. Polyoxometalates are well known as oxidation and acid catalysts in which the redox and acid-based properties can be tuned by variation of the structure type, the central heteroatom and addenda or transition-metal-substituted atoms. The catalytic function of the Keggin family has attracted much attention particularly because these heteropolycompounds (HPA) provide a good basis for the molecular design of mixed oxide catalysts and high capabilities in practical uses. On the other hand, H2O2 is one of the oxidants frequently used in fine chemicals synthesis, as an option to the conventional ones, since its use leads to a cleaner technology because it is easy to handle and its reaction produces only H2O as by-product. The selective catalytic of sulfides to sulfoxides has been a challenge for many years, owing to the importance of sulfoxides as intermediates in organic synthesis. Sulfones are also important compounds employed in the preparation and functionalization of a wide variety of products by stabilizing a-radicals, a anions and acting as cationic synthons. The main objective of this investigation was studied the influence of H5PMo11Al0.5V0.5O40, with Keggin structure, in selective oxidation of sulfides to sulfoxides or sulfones, with hydrogen peroxide 35 % (p/v). The amount of catalyst used was 1 % (mmol) in relation to inicial reactive, using reaction conditions showed in Scheme 1, high conversion and excellent selectivity was obtained to sulfoxides or sulfones. The better reaction conditions for selective oxidation of methyl phenyl sulfide to sulfoxides 2, with hydrogen peroxide were: room temperature, molar sustrate to hydrogen peroxide ratio of 1:28, acetonitrile as solvent and 1 % (in mmol) of H5PMo11Al0.5V0.5O40 as catalysts. For these conditions, the conversion was 100 % by reactive, at 1 h of reaction time, with selective to sulfoxides 2 of 99 %. On the other hand, the better reaction conditions for selective oxidation of methyl phenyl sulfide to sulfone 3 (100% selectivity and conversion, respectively) for 2 h of reaction time. The presence of V is very important on the oxidative catalytic activity to obtain both products. In order to establish the general applicability of these experimental conditions, various functionalized sulfides were subjected to the oxidation protocol.