[Cl:1]C1C(C#N)=NC(Cl)=C(Cl)C=1Cl.F[C:14]1[C:15]([C:23]#[N:24])=[N:16][C:17]([F:22])=[C:18]([F:21])[C:19]=1[F:20]>[Cl-].C([P+](CCCC)(CCCC)CCCC)CCC.C(Cl)Cl>[Cl:1][C:14]1[C:15]([C:23]#[N:24])=[N:16][C:17]([F:22])=[C:18]([F:21])[C:19]=1[F:20]A mixture of 3,4,5,6-tetrachloropicolinonitrile (16.1 g, 66 millimoles (mmol)) and 3,4,5,6-tetrafluoropicolinonitrile (5.9 g, 33 mmol) were heated to 160° C. under nitrogen to form a solution. To this stirred solution was added tetrabutyl phosphonium chloride (Bu4PCl; 0.36 g, 1.2 mmol), and the solution was held at 160° C. for 1 h. An aliquot was dissolved in methylene chloride (CH2Cl2) and passed through a short pad of silica gel before GC analysis. The profile of halogenated picolinonitriles was: 11.2% Cl4—PN; 11.3% 4,6-F2—PN; 2.3% 5,6-F2—PN; 19% 3,6-F2—PN; 52.6% 6-F—PN and 3.6% 4-F—PN. About 80% of the mixture is useful in the halogen exchange reaction to produce 3-chloro-4,5,6-trifluoropicolinonitrile.
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