Patent ID: 8686185

Claim:
A method for preparing 2-hydroxy-5-phenylalkylaminobenzoic acid derivative represented by Chemical formula 4 or its salt at a purity of at least 99%, comprising a step of preparing alkyl 2-hydroxy-5-phenylalkylaminobenzoate represented by Chemical formula 3 by reacting phenylalkyl methanesulfonate represented by Chemical formula 1 with alkyl 5-aminosalicylate represented by Chemical formula 2: wherein in the Chemical formulas 1 to 4, n is an integer from 2 to 4; R 1 , R 2 , R 4 and R 5 are hydrogen; R 3 is independently hydrogen, halogen, C 1-4 haloalkyl, nitro, hydroxy, C 1-4 alkyl, aryl, C 1-4 alkoxy or amine; A is hydrogen or C 1-3 alkyl; and B is hydrogen or acetyl; wherein the method comprises hydrolyzing alkyl 2-hydroxy-5-phenylalkylaminobenzoate represented by Chemical formula 3 to form 2-hydroxy-5-phenylalkylaminobenzoic acid sulfate; wherein the method comprises controlling the pH of the 2-hydroxy-5-phenylalkylaminobenzoic acid sulfate for purification; and wherein the purity of the 2-hydroxy-5-phenylalkylaminobenzoic acid derivative represented by Chemical formula 4 or its salt is at least 99%.