Friedel–Crafts acylation using sulfated zirconia catalyst

Synthesis of fine chemicals and intermediates by using Friedel–Crafts acylations is an important process in organic chemical technology. In most cases, very good yield and selectivity can be obtained with aluminium chloride as catalyst in conjunction with nitrobenzene as solvent. However, with modern environmental restrictions, in consonance with green chemistry, replacement of aluminium chloride–nitrobenzene or BF3–HF with solid catalysts has great industrial relevance. Acylation of benzene with 4-chlorobenzoyl chloride was attempted with different solid acid catalysts such as dodecatungstophosphoric acid (DTPA), DTPA/K-10 clay, K-10, Amberlite, Amberlyst-15, Indion-130, Filtrol-24 clay, and sulfated zirconia. However, only sulfated zirconia was found to be effective leading to 100% selective formation of 4-chlorobenzophenone, which is useful as an organic and pharmaceutical intermediate; for instance, in the manufacture of Cytrazin—a well known drug. The kinetics of the reaction was studied to establish that the reaction obeys the Langmuir–Hinshelwood–Hougen–Watson mechanism with very weak adsorption of the reactants. The reaction is intrinsically kinetically controlled.