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.