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

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.

A solid sulfanilic acid catalyst was found to be active in the solution state alkylation reaction. Alkylation of phenol yielded 57% conversion of phenol and shows 52% selectivity towards 4-tert-butylphenol.Figure optionsDownload high-quality image (137 K)Download as PowerPoint slideHighlights
► The immobilization of silica with sulfanilic acid has been done via a simple technique.
► The catalyst was active in the solvent free alkylation of phenol.
► The solvent free alkylation of phenol with tert-butyl alcohol at 120 °C gave a 57% conversion with 52% selectivity towards 4-tert-butylphenol.
► The catalyst was regenerated easily and reused many times without loss of activity.