Obtained by the oxidation of m-xylene: Smith, J. Am. Chem. Soc. 43, 1920 (1921); Weisemann, Fragen, Proc. 5th World Petrol. Congr. 4, 197 (1960); Brill, Ind. Eng. Chem. 52, 837 (1960); Bhattacharyya, Ganguly, J. Indian Chem. Soc. 38, 463 (1961); Saffer, Barker, US 3089906 (1963 to Mid-Century Corp.); Hay, GB 951192 (1964 to General Electric).