Background: The synthesis of high value risedronic acid is not fully resolved, as, for the
time being, the best method based on the preparation from 3-pyridylcarboxylic acid by reaction
with phosphorus trichloride in methanesulfonic acid gives risedronic acid in a good yield, but in an
Methods: Alternative protocols realizing the synthesis in sulfolane as the solvent and/or in the
presence of suitable IL additive were developed to obtain the target dronic acid in a pure form.
Results & Conclusion: Using phosphorus trichloride and phosphorous acid in two equivalents
quantities together with 0.6 equivalents of [bmim][BF4] without any solvent, the method afforded
the target dronic acid in a yield of 66% in a pure form.