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Dual‐parameter correlations on rate of dehydration step of a condensation reaction in aqueous solutions of ethanol, propan‐2‐ol and 2‐methylpropan‐2‐ol
Author(s) -
Yangjeh A. Habibi,
Gholami M. R.,
Mostaghim R.
Publication year - 2001
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.438
Subject(s) - chemistry , aqueous solution , reaction rate constant , ethanol , solvent , hydrogen bond , reaction rate , kinetics , thermodynamics , computational chemistry , molecule , organic chemistry , catalysis , physics , quantum mechanics
The reaction kinetics of the dehydration step of the condensation reaction between phenylhydrazine and benzaldehyde was studied spectrophotometrically in aqueous solutions of ethanol, propan‐2‐ol and 2‐methylpropan‐2‐ol at pH 11.5 at 25 °C. The apparent second‐order rate constants k 2app of the reaction increase with mole fraction of water in all the aqueous solutions. Single‐parameter correlations of log k 2app versus π* (dipolarity/polarizability), α (hydrogen‐bond donor acidity) and $E_{\rm T}^{\rm N}$ (normalized polarity parameter) were obtained in all the aqueous solutions. In all cases, the correlations versus $E_{\rm T}^{\rm N}$ and π* are acceptable, but correlations versus α are poor (e.g. in aqueous solutions of ethanol the correlation coefficients are 0.964, 0.967, and 0.751 respectively). The results of dual‐parameter correlations of log k 2app versus π* and α in all cases represent improvements with regard to the single‐parameter models (in aqueous solutions of ethanol r = 0.995; s.e. = 0.038; n = 13). The apparent second‐order rate constants of the reaction increase with α, π* and $E_{\rm T}^{\rm N}$ . Increasing the hydrogen‐bond donor acidity of the solvent stabilizes the activated complex of the reaction via hydrogen‐bond formation with the intermediate. A dual‐parameter equation of log k 2app versus π* and α was obtained for the combined data set of aqueous solutions ( n = 35, r = 0.989, s.e. = 0.062, F 2,32 = 719.21), in which π* has the major effect on the reaction rate relative to α. Copyright © 2001 John Wiley & Sons, Ltd.