Novel and environmentally benign Bronsted acidic ionic liqs. with SO3-H functionality were prepd. using N-methylimidazole, pyridine, triethylamine and 1,4-butanesultone as the source chems. The prepd. ionic liq. catalysts were characterized by NMR and their catalytic activity in tert-butylation of p-cresol with tert-Bu alc. was investigated. The effects of reaction time, reaction temp., reactant mole ratio and the recyclability of the catalysts on the conversion of p-cresol and selectivity to 2-tert-butyl-p-cresol and 2,6-di-tert-butyl-p-cresol called butylated hydroxytoluene (BHT) were investigated. Lower alc. to p-cresol mole ratios, lower ionic liq. to p-cresol ratio and temps. as low as 70°C gave 80% conversion of p-cresol. The catalyst activity was found to be almost completely retained even after 5 recycles. The extended Arrhenius equation was used to calc. the rate consts. for this reaction.