4635-82-9Relevant articles and documents
Deep cavitands provide organized solvation of reactions
Hooley, Richard J.,Rebek Jr., Julius
, p. 11904 - 11905 (2005)
Deep self-folding cavitands have been shown to stabilize the charged enolate intermediate of the α-deuteration of activated olefins by means of a network of organized solvation. Copyright
Elimination Reactions of β-Cyano Thioethers: Internal Return and the Lifetime of the Carbanion Intermediate
Fishbein, James C.,Jencks, William P.
, p. 5087 - 5095 (2007/10/02)
The E1cB elimination reaction of the pentafluorothiophenol adduct of fumaronitrile (3) in water containing 8.3percent Me2SO shows strong buffer catalysis and primary deuterium isotope effects of kH/kD = 4-5.In contrast, hydrogen exchange of the methanethiol adduct of 3 shows little or no buffer catalysis.There is no incorporation of deuterium that gives an inverse solvent isotope effect in the buffer-catalyzed elimination of the thionitrobenzoate adduct of 3 in D2O and H2O, although thiol anion expulsion is partly rate limiting for this reaction.These observations are consistent with internal return of the abstracted proton from the protonated buffer base that is competitive with the expulsion of leaving groups with pKa > 4.The primary deuterium isotope effects for elimination catalyzed by hydroxide ion are kH/kD = 4.9 +/- 0.4, 4.2 +/- 0.1, 4.2 +/- 0.3, and 3.1 +/- 0.1 for the pentafluorothiophenol and thionitrobenzoate adducts of 3, the N-methyl-2-mercaptopyridinium ion adduct of acrylonitrile (1), and the pentafluorothiophenol adduct of chloroacrylonitrile (2), respectively.These isotope effects are significantly larger than values of kH/kD = 2.6 +/- 0.3, 2.2 +/- 0.1, and 2.1 +/- 0.1 for buffer-catalyzed elimination from the adducts of 1 and 3.They are also larger than (1) the primary isotope effects of kH/kD = 2.5 +/- 0.3, 2.3 +/- 0.2, and 2.3 +/- 0.2 for the p-nitrothiophenol adducts of 1 and 3 and the thiophenol adduct of 2 that were obtained from the biphasic kinetics for elimination of these compounds in D2O and (2) the product discrimination isotope effects of ca. 3 for the addition of thiol anions to 1 and 3.These observations are consistent with the formation of an unstable carbanion intermediate that undergoes competitive reprotonation by solvent, k-1, exchange of the abstracted proton with the bulk solvent, ks, and elimination, k2.Ratios of k-1/ks and k-1/k2 that were obtained from the results give values of k-1 ca. 1E11 s-1 and k2 = 1E10-1E13 s-1, assuming a value of ks = 1E11 s-1.Estimated pKa values in aqueous solution include 26.8 for NCCH2CH2SPh, 22.0 for NCCH(Cl)CH2SPhNO2, and 23.2 for NCCH2CH(CN)SCH3.
