Abstract
AbstractVarious 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.
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