Preparation method of imma acid

The invention belongs to the field of medicine synthesis technology, and particularly relates to a preparation method of imma acid. The preparation method comprises the steps of: carrying out heating reaction on p-chloromethyl benzoic acid, piperazine and inorganic base in water to obtain 4-((piperazine-1-yl) methyl) benzoic acid; reacting the 4-((piperazine-1-yl) methyl) benzoic acid with methyl alcohol on the premise of a catalyst to obtain 4-((4-methyl piperazin-1-yl) methyl) benzoic acid; and filtering and filling hydrogen chloride to obtain imma acid. The method is simple in reaction operation, easy to control and low in cost, the yield reaches up to more than 93%, and the purity of imam acid reaches up to more than 99.6%.