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

TUNDO P.; ROMANELLI G.; VÁZQUEZ P.

Bologna - Italia

Congreso; VIII CONGRESSO INCA "Chimica sostenibile & Tecnologie ambientali: stato dell?arte e prospettive"; 2006

INCA

  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 sulfoxides also has been a challenge for many years owing the importance of sulfoxides as intermediates in organic synthesis. On 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 (HPA) 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 sulfoxide or sulfone depending of hydrogen peroxide concentration, at room temperature (r.t.), 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 HPA were used as catalyst: H3PMo12O40, H3PW12O40, H4SiMo12O40, H6PMo11AlO40, H4PMo11VO40 and H5PMo11Al0.5V0.5O40, respectively.   H6PMo11AlO40 gave rise to very high yields for 1-phenylethanol oxidation, for a reaction time of 7 h, 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 (r.t. 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 to corresponding sulfone.   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 HPA as catalyst. High yields and high selectivities characterize this methodology.