In this investigation we used methyl imidazolium hydrogen sulfate as an acidic ionic liquid for some functional groups interconversions. A selective and efficient procedure for the oxidation of sulfides to the corresponding sulfoxides is reported using ceric ammonium nitrate in the presence of methylimidazolium hydrogensulfate at 80 ?C. Deprotection of S , S -acetal compounds to their corresponding carbonyl compounds was carried out using NH 4 NO 3 /[Hmim]HSO4 at 80°C. Aldehydes were converted to the corresponding acylals in the presence of acetic anhydride and catalytic amount of methylimidazolium hydrogensulfate at room temperature. Acetylation of alcohols and phenols with acetic anhydride were carried out using methylimidazolium hydrogensulfate at 50 ?C under solvent-free conditions. Methylimidazolium hydrogensulfate as Br?nsted acidic ionic liquid ([ Hmim ]HSO 4 ) was used as an efficient catalyst in the Pechmann condensation of phenols with ?-ketoesters leading to the formation of coumarin under solvent-free conditions. Synthesis of 14-aryl or alkyl-14H-dibenzo[ a,j ]xanthenes by condensation of 2-naphthol and aldehydes in the presence of Methylimidazolium hydrogensulfate was carried out. Finally Methylimidazolium hydrogensulfate catalyzed three-component condensation reaction of an aldehyde, ?-ketoester and urea to afford the corresponding 3,4-dihydropyrimidin-2(1 H )-ones under solvent-free conditions.
