Wu, Hui, et al. “Synthesis of N-Substituted 1,3,5-Triazacyclohexanes Catalyzed by Starch Sulfuric Acid”. Asian Journal of Chemistry, vol. 22, no. 2, Mar. 2010, pp. 1097-02, https://asianpubs.org/index.php/ajchem/article/view/11233.