Acid–base equilibria in systems involving substituted pyridines in polar aprotic protophobic media and in the amphiprotic methanol

Activation and Deactivation of Cp*Ir(TsDPEN) Hydrogenation Catalysts in Water

“…[11] Using the correlations of pK a 's of pyridines in other sol- 2+ . [19] The lability of the HTsDPEN ligand in the unsaturated [1HH] 2+ is attributed to the high acidity of the dicationic tosylamine complex.…”

Potentiometric studies of cationic heteroconjugation equilibria in systems involving free and protonated pyridine derivatives in dimethyl sulfoxide

“…(8) The procedures for preparation and purification of 2,6-dinitrophenol, tetran-butylammonium 2,6-dinitrophenolate, tetra-n-butylammonium perchlorate, and tetra-nbutylammonium chloride were also described previously. (8,11) A cell for the e.m.f. measurements was assembled as follows: glass electrode | the system studied || modified calomel electrode.…”

“…It is quite striking that, in the amphiprotic methanol, a solvent regarded as rather unfavourable for conjugation equilibria, the cationic standard heteroconjugation constants could be measured for most of the substituted pyridine systems. (11) The lgK f • fell in the range 1.58 to 2.29. Consequently, it can be stated in general that the cationic standard heteroconjugation constants determined in systems involving organic N -bases, unlike those with substituted pyridine N -oxides, do not constitute a regular series.…”

“…The heteroconjugation reactions between protonated base BH + and free base B 1 were studied in o-dichlorobenzene, (1,2) chlorobenzene, (1,2) nitrobenzene, (3,4) nitromethane, (4,5) acetonitrile, (6)(7)(8) acetone, (9)(10)(11) propylene carbonate (12) and methanol (11) on the basis of conductometric, (1)(2)(3) solubility, (4,9) potentiometric, (6-8, 10, 11) and calorimetric (12) methods. The asymmetric hydrogen bond in (NHN) + bridges was also investigated by i.r.…”

“…It can be concluded that the tendency towards cationic heteroconjugation in systems of protonated pyridine derivatives and conjugate free bases in polar aprotic solvents like nitromethane, acetonitrile, and acetone is rather poor. (5,8,11) In most of the systems, the equilibrium is either completely absent or the equilibrium constants are so small that they cannot be measured potentiometrically. It is quite striking that, in the amphiprotic methanol, a solvent regarded as rather unfavourable for conjugation equilibria, the cationic standard heteroconjugation constants could be measured for most of the substituted pyridine systems.…”