EFFECT OF PRESSURE ON THE THERMOLYSIS OF NITROALKANES IN SOLUTION

The effect of pressure up to 1.1 GPa on the rates of decomposition of two acidic nitroalkanes, nitromethane and 2-nitropropane, was measured. The mechanisms of thermolysis are inferred from kinetic studies and product analysis. The rate-controlling step for nitromethane decomposition in toluene at 230 °C at low pressures is homolysis of the C−N bond. Beyond 20% conversion, the decomposition is autocatalytic. At high pressure, nitromethane has another reaction path which supplants homolysis. It is proposed that nitromethane forms an intermediate by cyclization of its aci-form. The high-pressure process is characterized by a first-order rate law without primary kinetic isotope effect, a low activation energy (28.5 kcal/mol), a negative activation volume (−5.5 mL/mol), and formation of products which cannot be attributed to radical intermediates. At high conversion, the reaction becomes autocatalytic as a result of accumulation of water leading to formation of products explainable by the Nef reaction. 2-Nitr...