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ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 24, Number 9
BKCSDE 24(9)
September 20, 2003 |
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Title |
Applications of Third Order Models in Solvolytic Reaction of Aliphatic Substituted Acyl Derivatives in 2,2,2-Trifluoroethanol-Ethanol Systems
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Author |
Zoon Ha Ryu, Gui Taek Lim, T. William Bentley
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Keywords |
Solvolysis, Kinetics, Acyl chlorides, Solvent effects
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Abstract |
Rate constants at various temperatures and activation parameters are reported for solvolyses of acyl chlorides (RCOCl), with R = Me, Et, i-Pr, t-Bu, cyclopentylmethyl, benzyl, thiophenylmethyl, 2-phenylethyl, diphenylmethyl, and phenylthiomethyl in 100% ethanol, 100% 2,2,2-trifluoroethanol (TFE) 80% v/v ethanol/ water and 97% w/w TFE/water. Additional rate constants for solvolyses with R = Me, t-Bu, and PhCH2 are reported for TFE/water and TFE/ethanol mixtures, and for solvolyses with R = t-Bu, and PhCH2 are reported for 1,1,1,3,3,3-hexafluoropropan-2-ol/water mixtures, as well as selected kinetic solvent isotope effects (MeOH/MeOD and TFE). Taft plots show that electron withdrawing groups (EWG) decrease reactivity significantly in TFE, but increase reactivity slightly in ethanol. Correlation of solvent effects using the extended Grunwald-Winstein (GW) equation shows an increasing sensitivity to solvent nucleophilicity for EWG. The effect of solvent stoichiometry in assumed third order reactions is evaluated for TFE/ethanol mixtures, which do not fit well in GW plots for R = Me, and t-Bu, and it is proposed that one molecule of TFE may have a specific role as electrophile; in contrast, reactions of substrates containing an EWG can be explained by third order reactions in which one molecule of solvent (ethanol or TFE) acts as a nucleophile, and a molecule of ethanol acts as a general base catalyst. Isokinetic relationships are also investigated.
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1293 - 0 |
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