4-Imidazol-1-yl-butane-1-sulfonic acid or a novel liquid salt? The NMR analysis and dual solvent-catalytic efficiency for one-pot synthesis of xanthenes

• Main Authors: Khaligh, Nader Ghaffari, Lim, Shi Teng, Ong, Chiu Ling, Johan, Mohd Rafie, Juan, Joon Ching
• Format: Article
• Published: Elsevier 2019
• Subjects: Q Science (General); QD Chemistry
• Online Access: http://eprints.um.edu.my/20066/; https://doi.org/10.1016/j.molliq.2019.01.041
• Institution: Universiti Malaya

The reaction of the equimolar mixture of imidazole and 1,4-butane sultone was performed at 90 °C in ethylbenzene for 12 h, and the structure of the product was investigated by the NMR analysis in CD3OD and DMSO‑d6. This work demonstrated that 4-imidazol-1-yl-butane-1-sulfonic acid could not be obtained through the above reaction and the mixture of zwitterionic (I) and ionic (II) structure is produced. The structure of the liquid salt (I + II) was characterized and analyzed by 2D NMR. Then, the dual solvent-catalytic efficiency of the liquid salt (I + II) was studied for the synthesis of a variety of xanthenes under mild conditions which afforded the desired products in good to excellent yields within short reaction times. The recyclability of the liquid salt (I + II) was studied with an average recovered yield of 89% for three subsequent runs. The recycled liquid salt showed no significant loss of the catalytic activity even after three runs and its structure remain same as fresh liquid salt (I + II).