Preparation method of metoprolol

The invention discloses a preparation method of metoprolol. The method comprises the following steps: firstly, preparing p-hydroxyphenylethyl methyl ether and sodium hydroxide solution into an alkalescence solution, heating the alkalescence solution, mixing with heated epoxy chloropropane, and introducing into an extracting tower type reactor for reaction; meanwhile, introducing methylbenzene into the extracting tower type reactor for extraction, pumping reaction liquid into a rectifying tower after the reaction liquid enters a receiving groove, enabling the methylbenzene steamed out of the upper part of the rectifying tower and a small quantity of the epoxy chloropropane to enter the extracting tower type reactor from the bottom for continuous reaction, thus obtaining an intermediate (II) at the bottom of the rectifying tower, and then carrying out ammonolysis reaction on the intermediate (II) and isopropylamine, thus obtaining the metoprolol. The method provided by the invention is simple and environment-friendly in operation, the dosage of alkali is accurately controlled by adjusting a pH value, and thus the open-loop side reaction on the epoxy chloropropane and the intermediate is reduced. In addition, by adopting the tower-type continuous reaction, the time is shortened by a large margin, and the dosage of the epoxy chloropropane is reduced, so that the open-loop side reaction is correspondingly reduced, and the quality and yield of a product are improved.