The invention relates to large-loop type
veterinary medicine antibiotics, in particular to a method for preparing
tulathromycin. The method mainly solves the problem that in the prior art, the dosage of n-
propylamine is large, and also solves the technical problems that due to the large dosage of n-
propylamine, a crude product is not high in content and poor in character, and
phosphate needs to be formed, neutralized and purified. The method comprises the steps that an
epoxy intermediate, ethyl
alcohol or isopropanol and N-benzyl
propylamine are added into a reactor and stirred fully and evenly, and then heating and stirring are carried out for a reaction; after the reaction is finished, a
solvent is removed,
acetone is added, and the mixture is evenly stirred and then transferred into a
pressure reactor; a
palladium carbon catalyst is added in the
pressure reactor,
hydrogen is introduced, a reaction is carried out under stirring, the catalyst is recycled through filtering after the reaction is finished, concentration is carried out to remove the
solvent, then water is added, filtering is carried out, separated-out solids are collected and subjected to
vacuum drying, a
tulathromycin crude product is obtained, and a fine
tulathromycin product is obtained after recrystallization.