Multiphase oxidation of alcohol and sulfides with hydrogen peroxide catalyzed by heteropolyacids

P. TUNDO, G. ROMANELLI, P. VÁZQUEZ

Dresden, Alemania

Conferencia; 1st International IUPAC Conference on Green Chemistry; 2006

IUPAC

The selective oxidation of organic substrates is a very important transformation in organic synthesis as these products are intermediate for many drug, vitamins and fragrances. The oxidation of alcohols to aldehydes to ketones represents one of the fundamental preparative reactions and several methods have been studied to accomplish this conversion. Although these procedure are most frequently accomplished but the use of toxic, corrosive and expensive oxidant Cr (VI) and manganese complexes in amount ranging from stechiometric to large excess. Oxidation of sulfides to sulfóxidos also has been a challenge for many years owing the importance of sulfoxides as intermediates in organic synthesis. In the other hand, the use of aqueous hydrogen peroxide as an oxidant is very attractive in industrial technology since hydrogen peroxide is cheap, environmentally, clean and easy to handle. In this work we reported a multiphase catalytic system consisting of hydrocarbon solvent (isooctane), aqueous phase, phase-tranfer (PT) agent (Aliquat 336), diluted hydrogen peroxide and Keggin heteropolyacid catalyst, afford the efficient oxidation of benzylic and secondary alcohols at 70°C, in moderate time reaction. The reaction gives very good yields. Similarly sulfides give sulfóxido or sulfona depending of hydrogen peroxide concentration, at room temperature with high yields and selectivity. The result of the preliminary investigation on the multiphase oxidation of 1-phenylethanol and thioanisol as models substrates on the effects of various parameters on the oxidations of alcohol and sulfides are given. The following heteropolyacid were used as catalyst: H3PMo12O40, H3PW12O40, H4SiMo12O40, H6PAlMo11O40, H4PMo11VO40 and H5PMo11Al0.5V0.5O40. H6PAlMo11O40 gave rise to the very high yields for 1-phenylethanol oxidation. In fact after a reaction time of 7 hours 99 % of yield of acethophenone. Benzyl alcohol was oxidized selectively to benzaldehyde. Larger excesses of hydrogen peroxide over the substrate lead only small amounts of benzoic acid. The thioanisol oxidation in multiphase system under optimized conditions (room temperature and 1:1.1 molar ratio of substrate:hydrogen peroxide is found to be ideal for complete conversion of sulfide in sulfoxide. Large excesses of hydrogen peroxide gave de corresponding sulfona. As conclusion, multiphase system is an excellent medium for the oxidation of benzylic and secondary alcohols to the corresponding carbonyl compounds and sulfides to the corresponding sulfoxide or sulfone with dilute hydrogen peroxide, employing Keggin heteropolyacid as catalyst, under multiphase condition (Aliquat 336). This metodology is characterized by high yields and selectivities.