NaHSO4•H2O Catalyzed Synthesis of Coumarin Derivatives under Solvent-Free Conditions

Nine 4-methylcoumarin derivatives were synthesized from phenols and ethyl acetoaceate at a molar ratio of 1 : 1.2 via Pechmann condensation using NaHSO4 center dot H2O (10 mol%) as catalyst under solvent-free conditions. The method was simple, green and efficient, and the reaction time was ranged from 3 to 5 h with the yields from 23% to 91%. The effects of substitution groups in the different positions of the aromatic ring on the reaction were investigated. The results showed that the activation group substituted on phenols, such as hydroxyl group or amino group, was favorable to the condensation reaction, but one more substitution group on the aromatic ring was less favorable to the reaction, the electron-withdrawing group substituted on phenols, such as nitro-group, led to no reaction or poor yields.