Ramazani, Ali, Issa Amini, and Abdolhossain Massoudi. 2010. “Kaolinite Powder As an Efficient Catalyst for the Preparation of Coumarins from in Situ Generated Stabilized Phosphorus Ylides in Solvent-Free Conditions”. Asian Journal of Chemistry 18 (1):120-24. https://asianpubs.org/index.php/ajchem/article/view/21267.