A Comparative Study of the Hydrogenation of 1,3,5-Trinitrobenzene and 2,4,6-Trinitrotoluene over a Copper–Alumina Catalyst in a Flow Reactor

The catalytic properties of a copper–alumina catalyst prepared from double layered hydroxide have been studied in the hydrogenation of 1,3,5-trinitrobenzene (TNB) and 2,4,6-trinitrotoluene (TNT) in a flow reactor. The reaction was carried out at a temperature of 120°C, a total pressure of 30 bar, and a substrate concentration of 0.10–0.15 M using methanol as a solvent. 1,3,5-Triaminobenzene (TAB) and 2,4,6-triaminotoluene (TAT) were isolated from the reaction mixture in the form of the double salts with sulfuric acid TAB⋅2H2SO4 and TAT⋅2H2SO4, the yields of which were 92 and 98%, respectively. At an initial trinitroarene concentration of 0.10 M, the hydrolysis of triaminobenzene salts made it possible to synthesize phloroglucinol and methylphloroglucinol in 78 and 91% yields, respectively. Increasing the concentration to 0.15 M reduced the yields to 71 and 88%, respectively. According to thermal analysis data, the observed differences in the yields of triaminobenzene salts and polyphenols were explained by the formation of different amounts of resinous by-products on the catalyst surface in the course of trinitroarene hydrogenation. In the hydrogenation of TNT, a smaller amount of resins was formed, and this led to higher yields of TAT⋅2H2SO4 and methylphloroglucinol. This was probably due to the presence of an electron-donating methyl substituent, which slowed down the polycondensation of TAT molecules.