Rad-Moghadam, Kurosh, and Nasser Montazeri. “Coumarin Synthesis via Pechmann Condensation on Silica-Supported Sulfuric Acid Under Microwave Irradiation”. Asian Journal of Chemistry, vol. 21, no. 1, Mar. 2010, pp. 499-03, https://asianpubs.org/index.php/ajchem/article/view/18950.