Disclosed is a process for producing terephthalic acid. The process includes contacting p-xylene with a gaseous stream containing oxygen (O2) in presence of a homogeneous catalyst solution, at a reaction temperature of 180° C. to 195° C. to oxidize at least a portion of the p-xylene and form a product stream containing terephthalic acid, said homogeneous catalyst solution contains 350 ppm to 450 ppm cobalt (Co), 170 ppm to 270 ppm manganese (Mn), and 410 ppm to 510 ppm bromine (Br), wherein a Br/(Co+Mn) wt. % ratio is 0.5:1 to 1:1, and a Co to Mn wt. % ratio is 1.5:1 to 2:1.