Alcoholysis of trifluoromethyl groups attached to the pyridine ring

In dimethylformamide solution, trifluoroethoxylation and methoxylation of 5-chloro-3-trifluoromethylpyridine (2) yield 5-chloro-3-tris(trifluoroethoxyl)methyl pyridine (2a) and a dimethyl ketal of 3-chloronicotinic acid anhydride (2b) with fluorines as leaving groups, respectively. The corresponding reactions of 2,3-dichloro-5-trifluoromethylpyridine (3) only yield the 2-alkoxy-substituted products 3a and 3b with chloro as the leaving group and the 2-dimethylamino product 3c which was formed by the action of solvent dimethylformamide as a nucleophile. Differences in their reaction behaviour and possible mechanisms are also discussed.