The invention discloses a refining method of 4-phenylaminopiperidine
analgesic, comprising the following steps of firstly preparing an
acid salt from the 4-phenylaminopiperidine
analgesic, purifying the
acid salt after recrystallization, alkalizing the salt again to obtain free basic groups, adding another acid to the mixture to obtain another
acid salt, re-crystallizing and refining the obtainedanother acid salt by a second
solvent to obtain the acid salt. According to the invention, the process is simple, the used agents are simply and easily obtained, and only twice salifying operation and recrystallization operation are needed; and by utilizing the refining method, the content of impurities is remarkably reduced, the purity reaches the weight standard associated with the
pharmacopoeia, the purity and the yield of
fentanyl compound acid salts prepared from
fentanyl compound free basic groups are remarkably improved, the production cost is reduced, and the production efficiency is remarkably improved.