Preparation method of piperaquine derivative

The invention discloses a preparation method of a piperaquine derivative III, namely, 1,4-bi(7-chloroquinolin-4-yl)piperazine. The piperaquine derivative III is a piperaquine dimmer impurity and is one of main impurities of crude drugs or preparations of piperaquine and piperaquine salt. The piperaquine derivative III can be used for analyzing and detecting the purity of chemicals piperaquine and piperaquine salt, thereby controlling the quality of piperaquine and piperaquine salt.