Nucleophilic Substitution Reactions of 2,4-Dinitrobenzene Derivatives with Hydrazine: Leaving Group and Solvent Effects

Abstract

The hydrazinolysis of 2,4-dinitrophenyl acetate in methanol proceed exclusively through acyl-oxygen scission by a concerted mechanism. The reaction of 1-chloro-2,4-dinitrobenzene with hydrazine in methanol, acetonitrile and dimethyl sulfoxide undergo uncatalyzed substitution and the formation of the zwitterionic intermediate is the rate-determining step. While 2,4-dinitrobenzene derivatives 1, 2, 3, 4, 5a-i, 6 with hydrazine in DMSO undergo uncatalyzed substitution and the departure of the leaving group is the rate-determining step. 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 reactivity of compounds 5a-i depends on the substituent of the thioaryl ring while the small ?Y value is due to the sulfides existing preferentially in the skew conformation. The small ?lg value (-0.18, r = 0.99) indicated that the reaction of sulfides with hydrazine proceeds with advanced bond formation to the nucleophile and the bond cleavage proceed in a slow extent in the transition state.