[Cl-].[CH3:2][C:3]1[CH:8]=[C:7]([NH:9][C:10](=[O:18])[C:11]2[CH:16]=[CH:15][CH:14]=[CH:13][C:12]=2[CH3:17])[CH:6]=[CH:5][C:4]=1[C:19](=[O:27])C[N+]1C=CC=CC=1.[Cl-].CC1C=CC(C(=[O:44])C[N+]2C=CC=CC=2)=C(NC(=O)C2C=CC=CC=2C)C=1.[OH-].[Na+].Cl>CO.O>[CH3:2][C:3]1[CH:8]=[C:7]([NH:9][C:10](=[O:18])[C:11]2[CH:16]=[CH:15][CH:14]=[CH:13][C:12]=2[CH3:17])[CH:6]=[CH:5][C:4]=1[C:19]([OH:27])=[O:44]The isomer mixture of 1-{2-[2-methyl-4-(2-methylbenzoylamino)phenyl]-2-oxoethyl}pyridinium chloride and 1-{2-[4-methyl-2-(2-methylbenzoylamino)phenyl]-2-oxoethyl}pyridinium chloride obtained in the above Reference Example 6 (207.3 g, 0.544 mole) is suspended in methanol (0.4 L) and thereto is added a solution of sodium hydroxide (52.5 g, 1.31 mole) in water (0.6 L), and the mixture is stirred at 60-76° C. for about 4 hours to complete the reaction. To the reaction mixture is added concentrated hydrochloric acid (0.108 L) at the same temperature to adjust pH=1. The mixture is stirred under ice cooling for one hour, and the precipitated crystals are separated by filtration. The resulting crystals are washed with water and dried at around 60° C. to give the crude product (125.5 g, yield 85.6%). A part of this crude product (20 g) is recrystallized from methanol (340 mL) and dried at 60° C. to give the desired product (12.1 g, yield 60.5%, purity by HPLC 99.7%).
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