Research & Teaching Faculty

Default Header Image

Reactions of Tertiary Phosphines with Alcohols in Aqueous Media

TitleReactions of Tertiary Phosphines with Alcohols in Aqueous Media
Publication TypeJournal Article
Year of Publication2009
AuthorsMoiseev, DV, Patrick, BO, James, BR
JournalInorganic Chemistry
Volume48
Pagination239-245
Date PublishedJan
Type of ArticleArticle
ISBN Number0020-1669
KeywordsALDEHYDES, BENZYL, FACILE SYNTHESIS, LIGNIN, PHOSPHONIUM SALTS, QUINONE METHIDE
Abstract

The phosphines R2R’P [R = R’ = Me, Et, Pr-n, Pr-i, (CH2)(3)OH; Me2PhP and MePh2P] react with 2- or 4-hydroxybenzyl alcohols, including "lignin-type" vanillyl, syringyl, and alpha-methylvanillyl alcohols, in a 1:1 ratio in aqueous media, to give zwitterionic phosphobetaine products; these on treatment with aq HCl form the corresponding phosphonium chlorides in good to excellent yields. The syringyl derivative [3,5-(OMe)(2)-4-OH-C6H2CH2PEt3]Cl was structurally characterized by X-ray analysis. Kinetically, the reactivity of the benzyl alcohols, studied with the water-soluble [HO(CH2)(3)](3)P, decreases with substituents in the order 2-hydroxy > 4-hydroxy > vanillyl > syringyl > alpha-methylvanillyl, while 3-hydroxybenzyl alcohol is unreactive; the trend is consistent with reactivity requiring the presence of an ortho- or para-OH substituent in the aromatic ring of the alcohol, and that the reactions proceed via a carbocation species stabilized as a quinone methide. Triethylphosphine reacts with coniferyl alcohol at the C=C moiety to give a zwitterionic intermediate that is again converted by aq HCl to a phosphonium chloride; no reaction was observed with cinnamyl alcohol. The effect on a phenolic pK(a) by incorporation of a phosphonium substituent is also measured.

URL<Go to ISI>://000262011700032