Applied Catalysis A: General 399 (2011) 42–49 Contents lists available at ScienceDirect Applied Catalysis A: General journal homepage: www.elsevier.com/locate/apcata Solvent free liquid-phase alkylation of phenol over solid sulfanilic acid catalyst Farook Adam a,∗ , Kasim Mohammed Hello b , Tammar Hussein Ali a a School of Chemical Sciences, Universiti Sains Malaysia, 11800 Penang, Malaysia b Chemical Department, Collage of Science, Al-Muthanna University, Iraq article info Article history: Received 13 January 2011 Received in revised form 16 March 2011 Accepted 19 March 2011 Available online 26 March 2011 Keywords: Surface modification Sol–gel technique Sulfanilic acid Alkylation 4-tert-Butylphenol abstract Sulfanilic acid was immobilized onto rice husk ash via 3-(chloropropyl)triethoxy-silane to form an acidic solid catalyst denoted as RHAPhSO 3 H. The BET surface area was found to be 308 m 2 g -1 . Pyridine adsorp- tion study revealed the presence of Brønsted acid sites. The EDX analysis showed the presence of S (10.88%) and N (10.37%). The 29 Si MAS NMR showed the presence of T 2 ,T 3 ,Q 3 and Q 4 silicon centres. The three carbon atoms of the propyl group were evident from the 13 C MAS NMR together with a series of chemical shifts consistent with the presence of the benzene ring. In the alkylation of phenol using RHAPhSO 3 H 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. © 2011 Elsevier B.V. All rights reserved. 1. Introduction In recent years, the study of heterogenation of important organic ligands including important homogeneous catalysts onto suitable supports has seen increased interest due to the demand for green chemistry and environmentally friendly technologies. Rice husk (RH) is a by-product of the rice milling industry. These husks cause serious disposal and pollution problems due to the presence of a high content of silica. The controlled burning of RH in air leads to the formation of rice husk ash (RHA) which contains ca. 95% silica [1]. The main method of immobilization of the organic moi- eties was via the reaction of a particular molecule with the silanol groups on the silica surface. Typically such a process took about 12 to 24 h under reflux conditions [2–4]. In this respect, we had described the surface functionalization of silica with 3-(chloropropyl)triethoxysilane (CPTES) using a simple method which does not require toxic reagents [5]. The CPTES immobilized silica was used to heterogenize several organic molecules such as saccharine and melamine [6,7]. The alkylation of phenol is of great industrial importance. Some 450,000 tonnes of alkylated products like tertiary butylphe- nols are used in the industry per year. Mono-alkylphenols and di-alkylphenols are used in the manufacture of antioxidants, UV absorbers and for the production of phenolic resins [8,9]. Liter- ∗ Corresponding author. Tel.: +60 1 64069717; fax: +60 4 6574854. E-mail addresses: farook@usm.my, farook dr@yahoo.com (F. Adam). ature review reveals that these alkylation reactions are mostly carried out in the gas phase with high conversion of phenol [10,11]. However, gas phase reactions usually involve high temperature and pressure leading to high cost. Very few studies on the sol- vent state alkylation of phenol with tertiary butyl alcohol (TBA) have been published [12,13]. These solvent state reactions how- ever, usually show very low conversions, i.e., less than 50%. It will therefore be advantageous to find new environmental friendly catalysts and milder experimental conditions to increase output to reduce cost and satisfy the environmental needs at the same time. In this work, sulfanilic acid was immobilized onto silica from rice husk ash via CPTES to form an acidic solid catalyst. The catalyst was used successfully for the solvent free liquid-phase alkylation of phenol. Herein we report the preparation, characterization and the catalytic activity of this solid sulfanilic acid catalyst. 2. Experimental 2.1. Chemicals The chemicals used in this study were sodium hydrox- ide (Systerm, 99%), CPTES (Sigma–Aldrich, 95%), sulfanilic acid (Sigma–Aldrich, 99%), nitric acid (Systerm, 65%), toluene (J.T. Baker, 99.8%), acetic acid (Systerm, 99.5%), TBA (Merck, 99%), phenol (Scharlau, 99.5%), acetonitrile (Qrec, 99.9%) and acetophenone (Nacalai tesque, 99.9%). The rice husk (RH) was collected from a rice mill in Penang, Malaysia. All chemicals were AR grade or of high purity and used directly without further purification. 0926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2011.03.039