Method for preparing ambroxol trans-impurity 6,8-dibromo-3-(trans-4-hydroxycyclohexyl)-1,2,3,4-tetrahydroquiazoline

The invention relates to a novel technology for Febuxostat. The method for preparing the Febuxostat comprises the following steps of: reacting 2-hydroxy-5-cyano-benzaldehyde with NaSH in a solvent to obtain 3-formyl-4-hydroxythiobenzamide; reacting the 3-formyl-4-hydroxythiobenzamide with 2-halogenated ethyl acetoacetate, and closing the ring to obtain 2-(3-formyl-4-hydroxyphenyl)-4-methyl-5-ethyoxycarbonylthiazole; reacting 2-(3-formyl-4-hydroxyphenyl)-4-methyl-5-ethyoxycarbonylthiazole with hydroxylamine in a solution of formic acid to obtain 2-(3-cyano-4-hydroxyphenyl)-4-methyl-5-ethyoxycarbonylthiazole; reacting 2-(3-cyano-4-hydroxyphenyl)-4-methyl-5-ethyoxycarbonylthiazole with halogenated isobutene to obtain 2-(3-formyl-4-isobutoxyphenyl)-4-methyl-5-ethyoxycarbonylthiazole under the action of potassium carbonate; and finally, hydrolyzing to remove the ester group by using sodium hydroxide, thereby obtaining the product Febuxostat. The provided preparation method is simple in process and high in reproduc