Preparation method of minocycline hydrochloride

The invention provides a preparation method of minocycline hydrochloride. The preparation method comprises the following steps: 1) preparing sancycline: preparing the sancycline by taking demeclocycline hydrochloride as a raw material; 2) preparing 7-iodosancycline: under a strong acid condition, taking N-iodosuccinimide and the sancycline to react to prepare a reaction solution, namely the 7-iodosancycline; 3) preparing the minocycline hydrochloride: taking the 7-iodosancycline and dimethylaminotrimethyl tin to react in an amine solvent and an amide solvent under the action of a palladium complex catalyst to prepare a reaction solution, and adjusting the pH (Potential of Hydrogen) of the reaction solution to be 0.8 to 1.0 with concentrated hydrochloric acid; after de-coloring with active carbon, adjusting the pH of the reaction solution to be 3.8 to 4.0 with ammonia water; freezing and crystallizing; after filtering, drying a filter cake to obtain the minocycline hydrochloride. The minocycline hydrochloride prepared by the preparation method has the advantages of low cost, stable structure, few isomer impurities, low content of epimers and relatively high product purity.