Biocompatible ionic liquid [Betaine][H 2 PO 4 ] as a reusable catalyst for the substitution of xanthen-9-ol under solvent-free conditions.

An ionic liquid, namely [Betaine][H 2 PO 4 ], was found to be an efficient catalyst for the direct substitution reaction of xanthen-9-ol with different nucleophiles under solvent-free conditions. This catalytic system is easy to be operated and the following work-up procedure is simple, with the ionic liquid catalyst reusable for at least five cycles at a high catalytic activity level. In addition, the ionic liquid is easy to prepare and its raw materials are inexpensive and have good biocompatibility. Therefore, our study presents an intriguing and sustainable protocol for the direct substitution of alcohol.