Crown-Ether Phase-Transfer Catalysts for Reduction of Ketones,Oxidation of Olefins and Polymerization of p-Xylenedibromide

Various homogeneous and heterogeneous crown ether catalysts were prepared and applied as phase transfer catalysts for some reductions, oxidations and polymerizations. Among various crown ethers, 15-crown-5 seems the best to catalyze the reduction of ketones and aldehydes with sodium borohydride in nonpolar aprotic solvents. A granular entrapped 15-crown-5-polyacrylamide catalysts was also prepared and applied as a heterogeneous catalyst for these reductions which seem to obey pseudo-first-order kinetics with rate constant 10^?4–10⁵ s^?1. The steric effects of ketones and the effects of temperature and concentration of crown ethers, sodium borohydride and carbonyl compounds were also investigated. Among various crown ethers, 18-crown-6 is the best to catalyze the oxidation of olefins such as styrene, xylene and stilbene with potassium permanganate. Crown ethers were successfully applied as catalysts for anionic polymerization of p-xylenedibromide with sodium dithionite as an initiator.