Synthesis of substituted coumarins catalyzed by sawdust-SO3H. An efficient and environmentally benign solid acid catalyst under solvent-free conditions

The sulfonated sawdust (SD-SO3H) was easily prepared by treatment of sawdust, a biomass waste material, with chlorosulfonic acid and characterized by elemental analysis, SEM and TGA. The bio-degradable solid acid catalyst has been applied to the Pechmann condensation reaction of phenols with beta-ketoesters for the synthesis of coumarin derivatives under solvent-free conditions. This environmentally benign and inexpensive method has such advantages as simplicity in operation, high yields, low catalyst loading and short reaction time. The catalyst can be efficiently recycled with insignificant loss of activity.