1189586-09-1Relevant articles and documents
Suppression of common-ion return by amines: A method to measure rates of fast SN1 reactions
Streidl, Nicolas,Antipova, Anna,Mayr, Herbert
, p. 7328 - 7334 (2009)
(Chemical Equation Presented) Rate constants for solvolyses of benzhydryl chlorides, which take place on the 10 ms to minute time scale, have been determined in aqueous acetone and acetonitrile by conductometry, using conventional conductometers as well as stopped-flow techniques. Secondary and tertiary amines were used to suppress ion recombination (common-ion return) thus giving access to the ionization rate constants k1. The observed common-ion rate depressions can be rationalized by the correlation equation for electrophile-nucleophile combinations, log k(20 °C) = s(E + N), where electrophiles (here: carbocations) are characterized by the parameter Eand nucleophiles (here: chloride anions and solvents) are characterized by N and s. 2009 American Chemical Society.
Ionizing power of aprotic solvents
Streidl, Nicolas,Mayr, Herbert
supporting information; experimental part, p. 2498 - 2506 (2011/06/10)
Rate constants for the heterolysis reactions (SN1) of a series of chloro-diarylmethanes in aprotic solvents (dimethyl sulfoxide (DMSO), acetonitrile, carboxamides, etc.) have been determined conductometrically in the presence of amines or triphenylphosphane, which trap the intermediate ion-pairs and suppress ion recombination. The operation of SN2 mechanisms can be excluded because the observed first-order rate constants become almost independent of the nature of the nucleophilic additive when a certain concentration of nucleophile is exceeded. The heterolysis rate constants are used to calculate nucleofugality parameters Nf and sf for chloride in aprotic solvents according to the linear free-energy relationship lgak (25 °C) = sf(Nf + Ef). Ionizing powers YBnCl of these solvents were calculated according to the Winstein-Grunwald equation. Because the heterolysis rate constants in aprotic solvents correlate only poorly with dielectric constants or empirical solvent parameters such as Gutmann's acceptor numbers or ETN values, the most common solvent polarity parameters do not reliably predict ionization rates in aprotic solvents. The kinetics of the heterolyses of chloro-diarylmethanes in aprotic solvents have been studied conductometrically by suppressing ion recombination with amine additives. In this way it became possible to determine the ionizing power of aprotic solvents and compare them to those of protic solvents. Copyright
