[C:1](=[S:3])=S.[NH2:4][C:5]1[CH:6]=[C:7]2[C:12](=[CH:13][CH:14]=1)[CH:11]=[C:10]([C:15]([OH:17])=[O:16])[CH:9]=[CH:8]2.C(N(CC)CC)C.II.Cl.S([O-])([O-])=O.[Na+].[Na+]>O1CCCC1.O>[N:4]([C:5]1[CH:6]=[C:7]2[C:12](=[CH:13][CH:14]=1)[CH:11]=[C:10]([C:15]([OH:17])=[O:16])[CH:9]=[CH:8]2)=[C:1]=[S:3]Carbon disulfide (0.26 mL, 4.4 mmol) was added to a mixture comprising 6-amino-2-naphthoic acid (0.28 g, 1.5 mmol), tetrahydrofuran (1.0 mL), water (1.0 mL) and triethylamine (0.51 mL, 3.6 mmol), followed by stirring at room temperature for 24 hours. To the obtained reaction mixture, a tetrahydrofuran (1.0 mL) solution of iodine (0.41 g, 1.6 mmol) was dropwise added over a period of 5 minutes at 0° C., followed by stirring at 0° C. for further two hours. Thereafter, 1M hydrochloric acid (1.5 mL) and sodium sulfite (38 mg, 0.30 mmol) were added and mixed. The formed insoluble matter was collected by filtration and dried under reduced pressure. Then, carbon disulfide (2.0 mL) was added and thoroughly mixed. Then, the insoluble matter was collected by filtration to obtain 6-isothiocyanato-2-naphthoic acid as a cream-colored solid (0.32 g, yield: 96%, HPLC purity: 94%, HPLC retention time: 3.7 min). LC-MS ES-228 (retention time: 4.5 min, condition 1).
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