Electrophilic aromatic substitution. Part 35. Chlorination of 1,3-dinitrobenzene, 1-chloro-2,4-dinitrobenzene, and 2,4-dinitrotoluene with nitric acid and hydrogen chloride or chlorine in sulphuric acid or oleum

Abstract

Solutions of sulphuric acid or oleum containing HCl or Cl₂ and nitric acid have been found both to chlorinate and nitrate deactivated aromatic compounds. The kinetics and products of the chlorination of 1,3-dinitrobenzene and 1-chloro-2,4-dinitrobenzene in sulphuric acid or oleum containing HCl and nitric acid at 130 °C, and the kinetics and products of the chlorination of 2,4-dinitrotoluene at 90 °C in sulphuric acid or oleum containing Cl₂ and nitric acid, are reported. 1,3-Dinitrobenzene and 1-chloro-2,4-dinitrobenzene were predominantly chlorinated. 2,4-Dinitrotoluene gave approximately equal amounts of 6-chloro-2,4-dinitrotoluene and 2,4,6-trinitrotoluene. The results show that under these conditions, chlorination and nitration are competing electrophilic reactions, and that chlorination is less selective than nitration. Possible mechanisms for chlorination are discussed.