Uses of antioxidants in composite propellants formulation are unavoidable. These materials are added to propellants to afford stability during storage time. In this paper, synthesis of 2-t-butyl p-cresol intermediate for the preparation of A.O.2246 using Bronsted acidic ionic liquids as catalyst and solvent were investigated. Methyl-tert-butyl ether was used for tert butylation of para cresol and variable reaction parameters such as temperature, mole ratio, type and catalyst composition and time were optimized. Tert butylation of p-cresol gives two products, 2-tert-butyl p-cresol and 2, 6-di-tert-butyl p-cresol. Among ionic liquids, triphenyl (butyl-4-sulphonyl) phosphonium sulfonate, irrespective of the alkylating agent, is the most active catalyst. In the presence of triphenyl (butyl-4-sulphonyl) phosphonium sulfonate, 2-t-butyl p-cresol was the main product of reaction with 91.7% of selectivity and 73.2% of p-cresol conversion.