PURPOSE: To prepare purified hydrochloric acid, in high efficiency, by contacting a specific silicon compound with crude hydrochloric acid containing hydrogen fluoride, and removing the produced organic fluorosilane from the system.

CONSTITUTION: A nearly equimolar mixture of hydrochloric acid and hydrogen fluoride is produced as a by-product in the preparation of fluorochlorohydrocarbons by the fluorination of halogenated hydrocarbon. The mixture is added with about 1W10 equivalent, based on the contained hydrogen fluoride, of the silicon compound of formula I [X is Cl, OH or group of formula II (R1WR6 are 1W4C alkyl or phenyl)] (e.g. trimethylchlorosilane), and the produced organic fluorosilane (e.g. trimethylfluorosilane) is removed e.g. by distillation, liquid- liquid separation, etc. to obtain high purity hydrochloric acid.