Abstract:
In this work, the catalytic activity of indium incorporated silica from rice husk ash
(RHA-In) was studied for the liquid phase Friedel-Crafts benzylation of naphthalene (NA) in
III
presence of cyclohexane as solvent using benzyl chloride (C 6H5CH2Cl) as benzylating agent.
Reaction temperature and reactants molar ratios were the only factors considered in this study
to investigate the catalytic performance of RHA-In catalyst. The reaction temperature was
varied from 70 to 90 °C, whereas the different BC/NA molar ratios used in this study were
1:1, 1:2, 1:3 and 2:1. The total reaction time was fixed at 3hours for all reaction trials.
RHA-In catalyst was found to exhibit very high efficiency for this reaction for the
selective production of 1-benzyl naphthalene (1-BNA) as the major product (> 80 %) and 2-
benzylnaphthalene (2-BNA) as the minor product (< 20%). The activity of the catalyst was
found to increase with increasing reaction temperature and BC/NA molar ratio. At the
optimum reaction conditions (80 °C, 0.2g wt of catalyst and 1:3 BC/NA molar ratio) the
maximum percentage of BC conversion obtained was > 99%, whereas the highest registered
selectivity for 1-benzyl naphthalene (1-BNA) product was ≈ 83%.
The formation of
benzylnaphthalene products (BNA) is explained by the electrophilic attack of benzyl cation
(C6H5CH2+) on the naphthalene ring whose formation is facilitated by the activity of the
catalyst. The benzylation reaction was observed not to proceed in the absence of the catalyst
or over RHA-SiO2 support. -RHA-In was found reusable for this reaction several times
without any significant change in its catalytic performance. It was also found that the RHA-In
catalyst did not show any sensitivity to moisture.
