Solvent free liquid-phase alkylation of phenol over solid sulfanilic acid catalyst Original Research Article

Sulfanilic acid was immobilized onto rice husk ash via 3-(chloropropyl)triethoxy-silane to form an acidic solid catalyst denoted as RHAPhSO3H. The BET surface area was found to be 308 m2 g−1. Pyridine adsorption study revealed the presence of Brønsted acid sites. The EDX analysis showed the presence of S (10.88%) and N (10.37%). The 29Si MAS NMR showed the presence of T2, T3, Q3 and Q4 silicon centres. The three carbon atoms of the propyl group were evident from the 13C MAS NMR together with a series of chemical shifts consistent with the presence of the benzene ring. In the alkylation of phenol using RHAPhSO3H as the catalyst resulted in 95% conversion of tert-butyl alcohol at 120 °C with 52% selectivity towards 4-tert-butylphenol. The catalyst was reused several times without significant loss of catalytic activity.