A. H. Yangjeh, M. Gholami
Apr 1, 2003
Citations
0
Influential Citations
3
Citations
Journal
Indian Journal of Chemistry Section B-organic Chemistry Including Medicinal Chemistry
Abstract
Reaction kinetics of 1-fluoro-2, 4-dinitrobenzene with piperidine has been studied spectrophotometrically in aqueous solutions of methanol, ethanol, propan-2-ol and 2-methylpropan-2-ol at 10°C. The reaction in the aqueoussolutions is not catalyzed by nucleophile(piperidine). Second-order rate constants of the reaction decrease with increasing mole fraction of water and E T N (normalized polarity parameter). Therefore, polarity of the reactants of the reaction is higher than that of the activated complex. Single-parameter correlations of log k A vs E T N give satisfactory results (regression coefficients in aqueous solutions of methanol, ethanol, propan-2-ol and 2-methylpropan-2-ol are 0.988, 0.994, 0.995 and 0.996, respectively). Single-parameter correlations of logk A vs π*(dipolarity/polarizability) and a ( hydrogen-bond donor acidity) do not give acceptable results( fore example, in the all aqueous solutions regression coefficients are 0.893 and 0.789, respectively), hence π* and a are not individually major factors in determining the reaction rate. Dual-parameter correlations of logk A vs π* and a in the all solutions represent significant improvement in statistical factors with regard to the single parameter models. Dipolarity/polarizability and hydrogen-bond donor acidity (HBD) of media have parallel and approximately equal effects on the reaction rate. Increasing of hydrogen-bond donor acidity of media stabilizes piperidine via hydrogen bonding interactions (one of the reactants) and hence the reaction rate decreases. A dual-parameter equation of logk A vs π* and a is obtained in the all aqueous solutions (n=41, r=0.990, s.e=0.070, F 2 , 3 8 =968.10) in which π* and a have parallel and approximately equal effects on the reaction rate.