Comparative Study of 1,3,5-Trinitrobenzene and 2,4,6-Trinitrotoluene Hydrogenation over Copper-Aluminum Oxide Catalyst in a Flow Reactor

Abstract

The catalytic properties of a copper-aluminum oxide catalyst obtained from double layered hydroxide have been studied in hydrogenation of 1,3,5-trinitrobenzene (TNB) and 2,4,6-trinitrotoluene (TNT) in a flow reactor. The reaction was carried out at temperature of 120°C, total pressure of 30 bar and 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 double salts with sulfuric acid TAB⋅2H2SO4 and TAT⋅2H2SO4, the yield of which was 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. Increasing the concentration to 0.15 M reduces the yield to 71 and 88%, respectively. According to thermal analysis data, the observed differences in the yields of triaminobenzene salts and polyphenols are explained by the formation of different amounts of resinous by-products on the catalyst surface during hydrogenation of trinitroarene. Hydrogenation of TNT produces less resin, resulting in higher yields of TAT⋅2H2SO4 and methyl phloroglucinol. This is probably due to the presence of an electron-donating methyl substituent, which slows down polycondensation of TAT molecules.