Spherical carbon with SO3H groups as an efficient solid acid catalyst for 2,4,5-triphenyl-imidazole synthesis

Spherical carbonaceous solid catalysts with -SO3H group are prepared by hydrothermal carbonization of starch followed by carbonization at low temperatures and sulfonation with H2SO4. The concentration of introduced -SO3H is determined by the amount of polar groups on carbon materials surface, and a high -SO3H group concentration (2.15 mmol g−1) is achieved. The spherical carbonaceous solid acid is evaluated as catalysts for the condensation of 2,4,5-triphenyl-imidazole under free solvent. Remarkably high 2,4,5-triphenyl-imidazole yields (93 %) can be obtained efficiently (110 oC and 90 min) when HTS-400-SO3H was used as catalyst. The catalytic activity is determined by the acid concentration of carbonaceous solid surface. There is slight decrease in catalytic activity of HTS-400-SO3H after five runs. The starch-derived catalysts can be easily recovered by simple filtration and exhibited high activity for ten successive recycles.