Highly Selective Room Temperature Monoreduction of Dinitro‐arenes by Hydrogen Sulfide under Liquid–Liquid Biphasic Catalysis

Selective reduction of one of the nitro group present in dinitro aromatic compounds by a novel Zinin reagent, H₂S‐laden N‐methyldiethanolamine (MDEA) solution, has been explored in the presence of tetra‐n‐butyl phosphonium bromide as a phase transfer catalyst under the liquid–liquid mode of reaction. Under the room temperature reaction condition, reduction of 2,4‐dinitrotoluene (2,4‐DNT) with H₂S‐laden MDEA leads to the selective reduction of one nitro group present either at the fourth position to obtain 4‐amino‐2‐nitrotoluene (4A2NT) or at the second position to get 2‐amino‐4‐nitrotoluene (2A4NT). The reaction was very fast to achieve 100% conversion, and the selectivity of 4A2NT is much higher than the 2A4NT. A detailed parametric study was performed to analyze the effect of parameters on 2,4‐DNT conversion and selectivity of both the isomers. The apparent activation energy was found to be as high as 46.25 kJ/mol, and the reaction was found to be kinetically controlled. An empirical kinetic model has been developed to correlate with the conversion version time data obtained experimentally. The present system dealt with an industrial problem in dealing with H₂S, present in by‐product gaseous streams of many petroleum and natural gas industries. Novelties in the selective monoreduction lie in that fact that the reaction was done at room temperature (303 K), with a novel reagent, H₂S‐laden MDEA solution. Therefore waste‐minimization was effected to yield value‐added fine chemicals, that is, amines.