A solid sulfonic acid catalyst for the solvent free alkylation of phenol

Silica extracted from rice husk ash was functionalized with 3-mercptopropyltrimethoxysilane (MPTMS) and then oxidized to sulfonic acid at room temperature and pressure. The FT-IR analysis shows bands at 1354-1166 cm−1 due to the asymmetric and symmetric stretching of SO2 group. The 13C CP MAS NMR of RHAPrSO3H showed chemical shifts at 58.6, 12.1 and 23.0 ppm attributed to the three carbon atoms of the propyl chain. The pyridine acidity test showed strong bands at 1510, 1541 cm−1 in the FT-IR spectrum attributed to the Brønsted acid sites. In the alkylation of phenol using RHAPrSO3H, a conversion of ca. 75% was achieved at the reaction temperature of 120 °C. The catalyst could be regenerated by washing and drying at 185 °C for 24 h. The catalyst was reused several times without loss of catalytic activity.