Pyridine protic equilibria

S. Goswami, A. R. Chakravarty, and A. Chakravorty, Chemistry of ruthenium. 7. Aqua complexes of isomeric bis[(2-arylazo)pyridine]ruthenium(II) moieties and their reactions solvolysis, protic equilibriums, and electrochemistry, Inorganic Chemistry, vol. 22, no. 4, pp. 602—609, 1983. 

Apart from the qualitative observations made previously about suitable solvents for study, the subject of solvates has two important bearings on the topics of thermochemistry which form the main body of this review. The first is that measured solubilities relate to the appropriate hydrate in equilibrium with the saturated solution, rather than to the anhydrous halide. Obviously, therefore, any estimate of enthalpy of solution from temperature dependence of solubility will refer to the appropriate solvate. The second area of relevance is to halide-solvent bonding strengths. These may be gauged to some extent from differential thermal analysis (DTA), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) solvates of "aprotic solvents such as pyridine, tetrahydrofuran, and acetonitrile will give clearer pictures here than solvates of "protic solvents such as water or alcohols. 

Cyclic ketones cannot usually be dimerized to the corresponding -hydroxy ketones under protic conditions. An exception to this generalization is shown in equation (2S)P The 2,3-dioxopyrrolidine is quantitatively dimerized by being warmed briefly with ethanolic pyridine, or by attempted recrystallization from warm toluene. In this case, as in equation (27), the favorable equilibrium constant is no doubt related to the inductive effect of the amide C=0, which favors hydration and other addition reactions of the ketonic carbonyl. 

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