[N:1]([O-])=O.[Na+].[NH2:5][C:6]1[C:15]2[CH2:14][CH2:13][CH2:12][CH2:11][C:10]=2[C:9]([S:16]([OH:19])(=[O:18])=[O:17])=[CH:8][CH:7]=1.O.O.[Cl:22][Sn]Cl>O.[OH-].[Na+].Cl>[ClH:22].[NH:5]([C:6]1[C:15]2[CH2:14][CH2:13][CH2:12][CH2:11][C:10]=2[C:9]([S:16]([OH:19])(=[O:17])=[O:18])=[CH:8][CH:7]=1)[NH2:1]1 g of NaNO2 is added to a solution of 3 g of the acid obtained in step A in 10 ml of water and 2 ml of 30% sodium hydroxide. This solution is poured over 1 hour into 10 ml of concentrated HCl cooled to 5° C. After stirring for 3 hours at 5° C., a solution of 7.5 g of SnCl2.2H2O in 15 ml of concentrated HCl is added slowly while the temperature is maintained at 5° C. The mixture is left stirring for one and a half hours at RT and filtered, and the residue is dried under vacuum to obtain 2.86 g of the expected product.
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