4-Amino-2,2 -bipyridyl, basicity

Basicity measurements of 4-amino-2,2 -bipyridyl and some of its N-substituted derivatives have shown that, when an electron-withdrawing substituent is present, the protonation occurs at the distant ring and derivatives with electron-donating substituents are protonated at N(l) of the substituted ring [78JCS(P2)1215]. 

Unsubstituted and N-substituted bipyridyls 76 (R = H, Me, Ph, MeCO, 4-MeC6H4S02) were investigated for amino-imino tautomerism using basicity measurements and UV spectral data. The bipyridyls 76 (R = H, Me, MeCO) were shown to exist predominantly in the amino form both in aqueous solution and in non-polar media. The tautomeric equilibrium of 76 (R = 4-McC6H4S02), however, depends on the solvent polarity whereas the imino tautomer predominates in water and ethanol, significant amounts of the amino tautomer were observed in dioxane and cyclohexane (78JCS(P2)1215). 

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