Reactions in Microemulsion Media. Borohydride Reduction of Mono- and Dicarbonyl Compounds

摘要

Microemulsions were prepared at 26 deg from mixtures of hexanes (O), a 50:1 (w/w) solution (W) of 0.1 M KOH-NaBH4, and a 1.23:1 (w/w) mixture (S) of hexadecyltrimethylammonium bromide (HTABr) and 1-butanol. A pseudoternary phase map contained a significant microemulsion (micro E) region, and micro E's A and B were used for reduction of several monocarbonyl compounds BENZOPHENONE (1A), BENZALDEHYDE (2A), ACETOPHENONE (3A), and 1-PHENYL-1-OCTADECANONE (4A), an alpha,Beta-unsaturated ketone TRANS-4-PHENYL-3-BUTEN-2-ONE (6A), and a diketone 4-(4'-BENZOYLPHENYL)-2-BUTANONE (7A) at 26 deg. For comparison purposes, reductions were also performed in aqueous 2-propanol (2-PrOH A and 2-PrOH B) prepared by the substitution of 2-proponal for the S and O components of micro E's A and B. Generally, the reductions were slightly faster in the microemulsion media than in the corresponding aqueous 2-propanol media. With enone 6a, the influence of microemulsions on the competition between 1,2- and 1,4-reduction was determined. For the sodium borohydride reduction of ketones, microemulsion catalysis is more effective than phase transfer catalysis or the use of a tetraalkylammonium borohydride in a hydrocarbon solvent.