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

An ionic liquid, namely [Betaine][HPO], 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.