[Cl:1][C:2]1[CH:3]=[C:4]([CH:9]([NH2:11])[CH3:10])[CH:5]=[CH:6][C:7]=1[Cl:8].C(O)(=O)[C@H](C1C=CC=CC=1)O.[OH-].[Na+]>C(OC)(C)(C)C>[Cl:1][C:2]1[CH:3]=[C:4]([C@H:9]([NH2:11])[CH3:10])[CH:5]=[CH:6][C:7]=1[Cl:8]A solution consisting of 41 g of (RS)-1-(3,4-dichlorophenyl)ethylamine and 78 g of methyl t-butyl ether was heated to 45° C. while stirring, and a mixture of 14.6 g of L-mandelic acid and 90 g of methyl t-butyl ether was added thereto over about 30 minutes, followed by stirring at the same temperature for 30 minutes. Then, after cooled to 20° C. over 6 hours, the precipitated crystals were filtered, washed twice with 40 g of methyl t-butyl ether and dried to obtain 32.9 g of diastereomer salt. 82 g of a 5% aqueous sodium hydroxide solution was added to the crystals, followed by extraction twice with 10 g of methyl t-butyl ether. The solvent was distilled off from the resulting organic layer to obtain 18.2 g of (R)-1-(3,4-dichlorophenyl)ethylamine. This had the optical purity of 87.4%ee.
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