NUCLEOPHILIC DISPLACEMENTS BY ORGANOPHOSPHORUS COMPOUNDS.
Abstract
The kinetics of the formation of ketophosphonium salts from the reactions of aryl-substituted alpha-bromoacetophenones and alpha-bromopropiophenones with triphenylphosphine (TPP) were determined by a conductivity method. The small rho values (+0.44, 0.67) and activation parameters obtained indicates S(N)2 pathways for these reactions. The debromination of these species with TPP-ROH were found to be general acid catalyzed. The proposed mechanisms involve attack on bromine of a general acid coordinated (on carbonyl) haloketone by TPP with varying degrees of proton transfer in the transition state. The reaction of alpha-haloketones with phosphites to give alpha-ketophosphonates, probably by S(N)2 processes, and vinyl phosphates (Perkow reaction) were studied. Hammett plots of the kinetics of formation of vinyl phosphate from aryl-substituted alpha-bromo- and alpha-chloroisobutyrophenones gave rho values of 1.89 and 2.37. Attack on bromine was not observed and the chloroketones reacted faster than the corresponding bromoketones. A mechanism involving addition of triethylphosphite (TEP) to carbonyl carbon in a slow step with subsequent rearrangement of phosphorus to oxygen and loss of halide ion is proposed. The stereochemistry of the Perkow reaction has been determined. Reactions of haloketones with phosphinites and the relative nucleophilicities of P(III) reagents are discussed. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 08, 1970
- Accession Number
- AD0708517
Entities
People
- Edward W. R. Casper
- Howard Parnes
- Irving J. Borowitz
- Steven Firstenberg
Organizations
- Yeshiva University