South African Journal of Chemistry
On-line version ISSN 1996-840X
ILIKTI, Hocine et al. Reduction of α,β-unsaturated ketones using a Zn/NiCl2 system in aqueous media in the presence of anionic and cationic surfactants. S.Afr.j.chem. (Online) [online]. 2008, vol.61, pp. 31-36. ISSN 1996-840X.
The reduction of aromatic and aliphatic α,β-unsaturated ketones, namely acetophenone (1) and (-)-carvone (3) with a Zn/NiCl2 system in H2OorH2O/EtOH media in the absence or presence of anionic and cationic surfactants have been investigated and have shown remarkable results. The anionic sodium dodecyl sulphate (SDS), the cationic cetyltrimethylammonium bromide (CTAB) and the non-micelle-forming didodecyldimethylammonium bromide (DDAB) surfactants were utilized. The reduction of acetophenone in H2O medium gave only a low yield of 1-phenyl ethanol (2) in comparison with the yields which resulted when a H2O/EtOH medium was employed. The yields increased relatively in a H2O medium in the presence of cationic surfactants which showed a gradual increase at low concentrations following different patterns and sharp increases at 60 °C and pH 9. The reduction of (-)-carvone (3) with the same system in H2O medium gave relatively higher yields than that of acetophenone. In the presence of cationic surfactants CTAB and DDAB in aqueous medium the total reduction yield increased appreciably and sometimes reached 100 % in the presence of DDAB at a concentration of 0.98 X 10-2 mol L-1 at 60 °C. The effects of pH, combined metallic salts and different surfactant concentrations on the reduction of (-)-carvone have been also investigated. This paper focuses on the application of surfactants in the reduction of α,β-enones by metal/metallic chloride/H2O systems in the absence of organic solvents. This method displays regioselectivity and stereoselectivity. This method may also be considered as a contribution to the antipollution process by means of the elimination of organic solvents from the chemical process.
Keywords : Zinc/nickel chloride/H2O; reduction; hydrogenation; surfactants; sodium dodecyl sulphate (SDS); cetyltrimethylammonium bromide (CTAB); didodecyldimethylammonium bromide (DDAB).