Second-order rate constants and activation parameters have been determined for the reactions of trialkyl phosphites in alcoholic media with α-chloro- or α-bromo-acetophenones having various substituents in the benzene ring (3,4-Me2, 4-Me, H, 4-CI, and 4-l). Linear Hammett plots are consistent with the involvement of a common first intermediate in the rate-determining stage, leading to the formation of vinyl phosphate, α-hydroxyphosphonate, and acetophenone. The results provide the first kinetic evidence in support of the initial formation of the previously suggested betaine as a common intermediate in alcoholic solution. Further reaction then involves rearrangement to give the vinyloxyphosphonium species (and hence the Perkow product) or protonation followed by dealkylation to give the α-hydroxyphosphonate. Evidence for the possible formation of dehalogenated ketone via solvolysis of the α-hydroxyphosphonium intermediate is also presented.
|Number of pages||6|
|Journal||Journal of the Chemical Society, Perkin Transactions 2|
|Publication status||Published - jan. 1 1988|
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