Gautam, Naveen, et al. “Synthesis, Spectral Characterization and Antioxidative Evaluation of Substituted 4H-1,4-Benzothiazine and Their Sulfones”. Asian Journal of Chemistry, vol. 22, no. 7, June 2010, pp. 5380-8, https://asianpubs.org/index.php/ajchem/article/view/11757.