The Grignard Reaction of Propylene Oxide

Abstract

The reactions of propylene oxide with Grignard reagents (RMgX) in various ethers have been tested. Relations between the reaction conditions and compositions of obtained four alcohols (CH₃CH(R)CH₂OH, CH₃CH(OH)CH₂R, CH₃CH₂CH(R)OH and CH₃C(R)(OH)CH₃) were investi- gated, and the reaction mechanism was also studied. The Grignard reagents were prepared from ethyl bromide, ethyl iodide, isopropyl bromide, isopropyl iodide and bromobenzene; and diethylene glycol dimethyl ether, tetrahydrofuran, ether, n-butyl ether and anisole were used as solvents.
The proportions of propylene oxide to Grignard reagent did not show any influence on the distribution of alcohols, while they affected the ratio of alcohols to halohydrins. Yields of halohydrin increased with increasing ratio of Grignard reagent to propylene oxide. Organic groups in Grignard reagents did not affect the proportion of four kinds of alcohols, but with regard to halogens in the Grignard reagents, the steric factor affected the compositions of two kinds of halohydrin (CH₃CH(X)CH₂OH and CH₃CH(OH)CH₂X). As a significant difference in the compositions of alcohol was observed between ether and tetrahydrofuran (solvents), product distributions against the reaction time were investigated in the reactions between propylene oxide and halohydrins in both solvents. Finally, possible two courses for the formation of alcohols were infered. The Grignard reactions of aldehyde or ketone were investigated to confirm the proposed mechanism.