The Heterogenization of sulfanilic and sulfonic acids and their catalytic activity in the liquidphase alkylation of phenol

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Date
2011
Authors
Hussein Ali, Tammar
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Abstract
The new mesoporous silica modified with sulfanilic and sulfonic acids was synthesized by using rice husk ash (RHA) as the silica source. The solid catalysts were denoted as RHABzS03H and RHAPrS03H. The as-synthesized solid catalysts showed good textural and structural properties. The high-angle XRD diffraction pattern exhibited diffraction at 28 which corresponds to amorphous silica. The absence of sharp peaks suggests the material is not crystalline. The 29Si MAS NMR showed the presence of T2 , T3 , Q3 and Q4 silicon centres. The 13C MAS NMR confirmed that RHABzS03H had three chemical shifts consistent with the three carbon atoms of the propyl group and a series of chemical shifts consistent with the presence of the aromatic ring. The activity of the catalysts for the tert-butylation of phenol and some substituted phenols and derivatives of alcohol were observed to be positively influenced with increasing reaction temperature. However, it was negatively affected with increasing TBA: phenol molar ratio. The highest catalytic conversion (98 %) was observed over RHAPrS03H whereas highest selectivity was for 2-tert-butylphenol followed by 4-tert-butylphenol. The activity of the catalyst decreased in the order: phenol > a-cresol > m-cresol > p-cresol > 2- propanol > benzyl alcohol. The homogenous sulfanilic acid (un-supported) was less active compared to the heterogeneous catalyst. The catalysts were reused three times in the tert-butylation of phenol at the optimum conditions without significant loss in the activity.
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Keywords
Sulfanilic , Sulfonic acids
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