JIN, TONG-SHOU, RUI-QIAO ZHAO, and TONG-SHUANG LI. 2010. “An Efficient and Convenient Procedure for Preparation of 5-Arylidene Barbituric Acid Catalyzed by ZrO2 SO42- Solid Superacid With Grinding”. Asian Journal of Chemistry 19 (5):3815-20. https://asianpubs.org/index.php/ajchem/article/view/13284.