Example 16
A solution of Varenicline free base (20.0 g) in methylene dichloride (100 ml) was stirred with the aqueous solution of Malonic acid (11.82 g, 1.2 eq in 100 ml of water). The aqueous layer containing Varenicline malonate was stirred with methylene dichloride to remove the nitrosamine impurity by solvent extraction. Thereafter, follow the general procedure for the isolation of Varenicline base from the aqueous layer. Yield: 13.6 g