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
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.