화학공학소재연구정보센터
Inorganic Chemistry, Vol.37, No.26, 6827-6831, 1998
Oxidation of alcohols by hydrogen peroxide, catalyzed by methyltrioxorhenium (MTO): A hydride abstraction
Primary and secondary alcohols are oxidized using hydrogen peroxide as an oxygen donor and methyltrioxorhenium (MTO) as a catalyst. The methylrhenium di-peroxide, CH3Re(O)(eta(2)-O-2)(2)(H2O), was the dominant and reactive form of the catalyst. Representative rate constants k/L mol(-1) s(-1) are 1.02 x 10(-4) for 4-Me-alpha-methylbenzyl alcohol and 4.9 x 10(-5) for 4-Cl-alpha-methylbenzyl alcohol. There was a kinetic isotope effect of 3.2 for the alpha C-H bond. When sec-phenethyl alcohol was labeled with O-18, 80% of the oxygen was retained in the ketone. Tests for the possible intervention of a free radical intermediate were carried out; the evidence was entirety negative. A mechanism featuring hydride abstraction is proposed, the first time for the H2O2/MTO system. Also, a cocatalytic set of reaction conditions has been developed on the synthetic scale, using bromide and MTO as cocatalysts, which cuts the reaction time from hours to minutes.