Factors in the formation of isomerically and optically pure alkyl halides. Part VI. The preparation of optically pure 2-halogenobutanes

Abstract

Optically active 2-chloro- and 2-bromo-butane are formed, with little or no loss of enantiomeric purity, by the interaction of hydrogen halide (Cl, Br) with (+)-tri-s-butyl phosphite or (+)-s-butyl diphenylphosphinite. The reactions of optically active butan-2-ol with phosphorus trichloride, dichlorophenylphosphine, or chlorodiphenylphosphine similarly yield optically pure 2-chlorobutane, although some loss of rotatory power occurs in the reaction of butan-2-ol with phosphorus tribromide. 2-Iodobutane of maximum rotatory power is obtained only if hydrogen iodide is absent, e.g., in the reaction of di-s-butyl hydrogen phosphite with phosphorus tri-iodide. Values obtained for the rotations of the optically pure halides are confirmed by stereospecific conversion into s-butyl ethyl sulphide and are compared with previously reported data.