Preparation method of erythromycin 6,9 imino ether

The invention discloses a preparation method of erythromycin 6,9 imino ether. The method comprises the following steps: 1) with lower alcohols as reaction solvents, erythromycin thiocyanate reacts with hydroxylamine to generate thiocyanate salts of erythromycin; 2) water and water-immiscible low-polar organic solvents are added dropwise into the reaction mixture when the content of erythromycin detected with HPLC is less than 0.5%, lye is added into the mixture, after the mixture is fully mixed, to achieve a pH between 9 and 12, the mixture is allowed to stand to stratify, and a water layer is removed; 3) mesyl chloride or toluene sulfochloride is added into an organic layer for reactions of the Beckman arrangement to generate erythromycin 6,9 imino ether. The method provided by the invention simplifies operations by removing extraction of erythromycin oxime and salts of erythromycin oxime, and thus the conversion rate of erythromycin is improved and the cost of production equipment and energy is reduced. By