Kumar, J. K. Prashanth, et al. “Rapid and Efficient N-Tert-Butoxy Carbonylation of Amines Catalyzed by Sulfated Tin Oxide Under Solvent-Free Condition”. Orbital: The Electronic Journal of Chemistry, vol. 10, no. 7, Dec. 2018, pp. 503-8, https://periodicos.ufms.br/index.php/orbital/article/view/16023.