Premium
Dual‐parameter correlations on rate of an aromatic nucleophilic substitution reaction in aqueous solutions of methanol, ethanol, and propan‐2‐ol
Author(s) -
Gholami M. R.,
Yangjeh A. Habibi
Publication year - 2001
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/1097-4601(200102)33:2<118::aid-kin1003>3.0.co;2-u
Subject(s) - chemistry , piperidine , aqueous solution , polarizability , solvent , reaction rate constant , methanol , ethanol , hydrogen bond , reaction rate , solvent effects , nucleophilic substitution , medicinal chemistry , computational chemistry , organic chemistry , inorganic chemistry , kinetics , catalysis , molecule , physics , quantum mechanics
Reaction kinetics of 1‐chloro‐2,4‐dinitrobenzene with piperidine was studied spectrophotometrically in aqueous solutions of methanol, ethanol, and propan‐2‐ol at 25°C. The reaction in these solutions is not catalyzed by piperidine. The plots of second‐order rate constants of the reaction vs. mole fraction of water show maxima in the all‐aqueous solutions. Single‐parameter correlations of log k 2 vs. π* (dipolarity/polarizability), α (hydrogen‐bond donor acidity), and E T N (normalized polarity parameter) are very poor in the all solutions (for example, in aqueous solutions of ethanol, regression coefficients are 0.814, 0.113, and 0.486, respectively). Dual‐parameter correlations of log k 2 vs. π* and α in all cases represent significant improvement with regard to the single‐parameter models (in aqueous solutions of ethanol: n = 11, r = 0.980, and s = 0.034). Dipolarity/polarizability and hydrogen‐bond donor acidity (HBD) of media have opposite effects on the reaction rate. The activated complex leading to the zwitterionic intermediate is expected to be favored by increasing the solvent dipolarity/polarizability parameter. Increasing the hydrogen‐bond donor acidity of solvent stabilizes piperidine and hence the reaction rate decreases. A dual‐parameter equation of log k 2 vs. π* and α was obtained in the all‐aqueous solutions ( n = 31, r = 0.956, s = 0.055) in which π* and α have approximately equal and opposite effects on the reaction rate. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 118–123, 2001