NUCLEOPHILIC SUBSTITUTION REACTIONS OF 2, 4-DINITTROPHENYL ACETATE WITH HYDRAZINE AND METHANOL SOLVENT EFFECT

The generally accepted mechanism for nucleophilic aromatic substitution (the snare mechanism) is an addition-elimination mechanism and involves the formation of a Meisenheimer type of intermediate. The hydrazinolysis of 2,4-dinitrophenyl acetate in methanol proceeds exclusively through acyl-oxygen scission by a concerted mechanism. The process depends on the basicity of the leaving group and its steric hindrance as well as the possible intramolecular hydrogen bond in the transition state. The reactions of 2,4Dinittrophenyl Acetate with hydrazine obeyed pseudo-first-order rate constants (kobs). The linearplot of kobs vs. amine concentration indicated that there is no base-catalysis.The large negative ΔS# value indicates a rigid transition state or great participation of methanol molecules in the activated complex.