The present disclosure provides a composition for preparing terephthalic acid; said composition comprises p-Toluic acid in an amount of 0.05 % to 4 % with respect to the total mass of the composition; at least one catalyst in an amount of 0.02 % to 2.5 % with respect to the total mass of the composition; at least one ionic liquid in an amount of 0.04 % to 50 % with respect to the total mass of the composition; at least one carboxylic acid solvent; and p- xylene. The present disclosure also provides a process for preparing terephthalic acid.