Kinetics and mechanism of Halogen displacement reactions of Halonitrobenzenes with aliphatic amines: a comparative study

Abstract

The kinetics of the reaction of 2,4-dinitrochlorobenzene (DNCB)/2,4-dinitrofluorobenzene newline(DNFB) with aliphatic amines, n-butylamine (NBA), n-propylamine (NPA), isopropylamine newline(IPA), ethylamine (EA) and ethanolamine (EOA) were investigated in acetonitrile. newlineExperiments were conducted to determine and compare the effect of alkyl group of amine, newlineeffect of halogen, the effect of solvent polarity and effect of nitro group on the substitution newlinereaction. Theoretical calculations were performed using DFT methods to establish the effect of newlinechanging the alkyl group on the activation energy (Ea) of the reaction. The mechanism of EOA newlinereaction with DNFB was explored in detail to understand the formation of Meisenheimer newlinecomplex, effect of solvent polarity and to compare the reactivity of DNFB with that of MNFB. newlineAll kinetic runs were conducted under pseudo-first order conditions with respect to the newlinehalonitrobenzene in acetonitrile. The progress of the reactions were monitored by measuring newlinethe absorbance of the reaction mixture at regular intervals using Shimadzu UV-1800 newlinespectrophotometer (Shimadzu Corporation, Japan) equipped with thermo-stated cell holder. newlineThe kinetic data were acquired by using a PC equipped with UVProbe software designed for newlinekinetic measurements. The UV-VIS spectra of the reaction mixtures were determined at newlineregular intervals as a separate experiment to confirm exclusive formation of the products. The newlineHF and DFT methods used for estimating the energies of the reactants, transition states and newlineproduct were part of Spartan 08 software package (Wavefunction, Inc., USA). The calculations newlinein solvent medium were performed using SM8 available in Spartan 08. newlineThe measurement of rate constants of the reactions showed that the reaction follows newlinesecond order kinetics. A comparison of the second order rate constants for the various amines newlinev newlinerevealed that the reactivity order for the various amines towards halonitrobenzenes is newlineNBAgtNPAgtEAgtEOAgtIPA.