Study On The Chemoselective Hydrogenation Of3-Nitrostyrene To3-Aminostyrene

Functionalized anilines are important intermediates for agrochemicals, pharmaceuticals, pesticides and dyes, and other industrially important products, there is a strong incentive to develop chemoselective catalysts for the reduction of nitro groups. Most of the solvents used in NS hydrogenation reaction are toxic and volatile, such as THF, toluene, triethylamine etc. The reported Au, Ag noble metal supported catalysts have low activity and are easily poisoned when the pressurized CO2were introduced into the reaction system. Moreover, these catalysts sometimes show low selectivity to AS because they are active for the hydrogenation of both C=C and C=O bonds.In this paper, Pt catalysts supported on TiO2and ATO are prepared and examined in the hydrogenation of3-nitrostyrene to3-aminostyrene.(1) The selectivity to AS reaches88%in CO2-dissolved H2O at CO2pressures ranging from4MPa to10MPa. The main product is ENB with77%selectivity when the CO2pressure is>8MPa. The pressurization with CO2varies the product selectivity in the nonpolar solvent but not in the polar solvent; it also has a negative impact on the total conversion.(2) The Pt/ATO catalysts are inactive to the hydrogenation of C=C bond, whose selectivity to AS is always>97%at any conversion. The results showed that the change of Pt loading has no effect on the selectivity to AS. The accumulation of harmful intermediates such as hydroxylamine, nitroso-compounds, azo-compounds is negligible. With excessive impregnation and ultrasonic method, Pt particles are well dispersed on ATO and the Pt/ATO catalysts are chemoselective for the hydrogenation of3-nitrostyrene to3-aminostyrene. Both Pt and Sb species are electron-deficient, in contrast, the Sn species are electron-rich. Both Sn and Sb species that are rich on the surface layer of supports modify Pt particles.(3) Influence of Sn/Sb moler ratio on the performance of Pt/SnO2-Sb2O3was investigated. When the moler ratio of Sn to Sb is80, Pt/SnO2-Sb2O3gives the highest catalytic activity for the hydrogenation of nitrostyrene with a97.4%selectivity to aminostyrene. It is active for the hydrogenation of nitro group but inactive to C=C bond hydrogenation. Both Sn and Sb species that are rich on the surface layer of supports modify Pt particles.(4) Pt/TiO2-Sb2O3catalysts were prepared and used for the hydrogenation of3-nitrostyrene. When the Sb loading is1.4wt%, Pt/TiO2-Sb2O3gives the highest catalytic selectivity for the hydrogenation of nitrostyrene. Both Sn and Sb species that are rich on the surface layer of supports modify Pt particles.