The present invention relates to a process for preparing risedronic acid comprising the step of combining a 3-pyridyl acetic acid or a salt thereof, phosphorous acid, and a halophosporous compound selected from PCl
3
, PCl
S
, POCl
3
, PBr
3
, POBr
3
, and PBr
5
in the presence of a diluent that is either a bicyclic aliphatic hydrocarbon or a substituted cyclic aliphatic hydrocarbon or a mixture thereof, in combination with a codiluent, that is orthophosphoric acid
本发明涉及一种制备利福仙酸的方法,包括以下步骤:在存在一种稀释剂的情况下,将
3-吡啶乙酸或其盐、
磷酸和从PCl3、PClS、POCl3、PBr3、POBr3和PBr5中选择的卤
磷化合物组合,并与一种共稀释剂正
磷酸一起使用。其中,所述稀释剂为双环脂肪族碳氢化合物、取代环脂肪族碳氢化合物或其混合物。