Green and safe hydrogenation of 2,4-dinitrotoluene into 1-methyl-2, 4-cyclohexanediamine over the Ru/γ-Al2O3 catalyst

The direct hydrogenation of 2,4-dinitrotoluene (2,4-DNT) to 1-methyl-2,4-cyclohexanediamine (2,4-MCHD) represents a significant yet non-industrialized green process for synthesizing methylcyclohexane diisocyanate (HTDI), known for its excellent properties. This process faces considerable challenges due to the hydrogenation of the benzene ring, the reduction of two nitro groups, and the need to avoid deamination reactions. In this study, an alkali-free heterogeneous catalytic system was developed for the direct hydrogenation of 2,4-DNT to 2,4-MCHD using Ru nanoclusters supported on γ-Al 2 O 3 . Side reactions such as deamination were effectively inhibited, resulting in a 2,4-MCHD selectivity exceeding 95% and a 2,4-DNT conversion greater than 99%. Kinetic studies indicated that the hydrogenation of 2,4-DNT in this system operates as a tandem reaction, with the hydrogenation of the benzene ring serving as the rate-determining step. Structure-activity relationship studies demonstrated that the valence state of Ru nanoclusters, the acidity and basicity of the catalyst, and the synergistic effect between Ru and the support significantly influence catalytic performance. This work represents the first example of the direct hydrogenation of dinitroaromatic compounds to aliphatic diamines in a system that does not require the addition of alkali elements, thereby establishing a solid foundation for the further exploration of such reaction systems.