STUDIES ON NUCLEOPHILIC AROMATIC SUBSTITUTION REACTION OF SOME NITRO ACTIVATED SUBSTRATES IN APROTIC SOLVENTS

Abstract

A review on literature pertaining to aromatic nucleophillc substitution is given. Kinetics of the reactions of 0-(2',4'-dlnltrophenyl) 1.7.7 - trlmethyl blcyclo [2.2.1] heptan-2-one oxime, 0 - (2',4'- dlnltro phenyl) 3.5.5-trimethyl-2-cyclohexen-l-one oxime, 2,3 - [cyclopenten- 3'.5'-diyl]endo N-(2",4"-dinitrophenoxy) succlnimlde and 0-(2',4'-dlnltrophenyl)-4-phenyl-3-buten-2-one oxime have been studied with piperldine, cyclohexylamine, pyrrolidine, morphollne, n-butylamlne, and ethanolaminein some nonpolar and dipolar aprotlc solvents under pseudo-first order conditions at 35±0.1°C. The reactions have been followed spectrophotometrlcally at the A of the corresponding coloured amlnolysls product as a function of nucleophile concentration, solvent polarity and temperature. The site of nucteophi1ic attack is the aromatic carbon attached to oxime oxygen. The products of the reactions In each case are N-(2,4-dinitrophenyl) amine and the parent oxime In quantitative yield. These have been characterised by comparing t.l.c and spectral data with those of the corresponding authentic samples. The reactions of 0-(2',4'-dlnltrophenyl) 1.7.7- trlmethyl bicyclo [2.2.1] heptan-2-one oxime with piperldine, cyclohexylamine, ethanolamine and pyrrolidine In acetonitrile and also those with piperldine in acetonitrile, ethyl acetate, toluene and tetrahydrofuran are not catalysed. The reactions of 0-(2',4'-dlnitophenyl) 3,5,5 - trlmethyl -2- cyclohexen-1-one oxime with piperldine, n-butylamlne and pyrroli dine in acetonitrile are catalysed. The plots of second-order rate constants, k versus [Nu] are linear passing through the origin. ~r The reactions of this compound with pyrrolidine in ethyl acetate, acetonitrile, benzene and chlorobenzene are also catalysed. However, its reactions with ethanolamine in acetonitrile are not catalysed. 2,3-[cyclopenten-3',5'-diyl] endo N-(2",4"- dinitrophenoxy) succinimide reacts with pyrrolidine in ethyl acetate following a catalysed path. The plots of k ^ versus [Nu] in this case is linear with characteristic slope and intercept. However its reactions with piperldine, morphollne and cyclohexylamine In ethyl acetate and those with morphollne in acetonitrile, ethyl acetate, benzene and toluene are uncatalysed. The reactions of 0-(2' ,4' -dinitrophenyl)-4-phenyl-3-buten -2- one oxime with pyrrolidine in acetonitrile and benzene and those of piperidine in acetonitrile are catalysed. Studies on solvent effect reveal the polar nature of the transition state. The reactions of each of the four substrates have been carried out at various temperatures ranging from 20 to o 45 C and the relevant thermodynamic parameters calculated. Entropy of activation (AS ) values are high and negative Indicating congested nature of the transition state. A comparison of the literature data on aromatic nucleophilic substitution is given in chapter VII. Mechanistic interpretation is given in appropriate places.