Role of Intermolecular Reactions in Thermolysis of Aromatic Nitro Compounds in Supercritical Aromatic Solvents

Article abstract of DOI:10.1021/jo00010a025

Several nitroarenes were decomposed isothermally in dilute supercritical solution in benzene or toluene and in the vapor phase in the temperature range of 290-380 deg C in sealed glass tubes with pressure up to 100 MPa.The mechanisms of thermolysis are inferred from kinetic studies and product analysis.The initial rate-controlling step for nitrobenzene and p-nitrotoluene decomposition is probably intermolecular hydrogen abstraction to form an ArNO2H radical intermediate.The nature of the transition state is deduced from the activation volume (ΔV^*), H/D kinetic-isotope effect, and a linear free-energy relationship between the ionization potential of the hydrogen donor and the logarithm of the decomposition rate.A concurrent pathway for o-nitrotoluene is an intramolecular reaction in which anthranil is an intermediate.The behavior of 1,3-dinitrobenzene and 1,4-dinitrobenzene resembles that of nitrobenzene, whereas 2,4-dinitrotoluene and 2,6-dinitrotoluene decompose in the same manner as o-nitrotoluene.Activation parameters are given and detailed mechanisms proposed.