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

Potentiometric and ab initio studies of acid–base interactions of substituted 4-halo(Cl,Br)pyridine N-oxide systems

“…Our experience in studying these equilibria in polar aprotic protophobic solvents such as acetone [1,2], acetonitrile [1,3], benzonitrile [1,4], propylene carbonate [1,5], nitromethane [1,6], as well as in polar aprotic protophilic solvents, dimethylformamide [1,7], dimethyl sulfoxide [1,7,8], and the polar amphiprotic methanol [1,2,9] enabled the conclusion to be drawn that best results could be achieved by correlating experimental data obtained using the potentiometric titration technique with those computed by ab initio methods, e.g. Hartree-Fock and Møller-Plesset methods.…”

Basicity comparison for di-substituted 4-nitropyridine derivatives in polar non-aqueous media

“…On the other hand, dimethyl sulfoxide, a highly polar and strongly basic aprotic protophilic solvent as a medium, was chosen to avoid potential complications associated with establishing of intricate association equilibria as was the case with weak polar solvents. Additionally, to expand the area for drawing conclusions about the influence of the medium on establishing (acid + base) equilibria in systems with 4-nitropyridines studied, the values of acidity constants determined (expressed as pK a ) were compared with those previously obtained in another polar protophobic aprotic solvent, acetone (AC) [24], and with the results for the unsubstituted pyridine (Py) [9,10,12,25,26].…”

“…For this reason, (acid + base) equilibria occurring in the systems consisting of heterocyclic N-bases such as pyridine, quinoline, piperidine and their derivatives [8][9][10][11][12], as well as aliphatic and heterocyclic amine N-oxides [13][14][15][16][17][18] have been extensively investigated in our laboratory. Consequently, the values of acidity constants (expressed as pK a ) for variety of heterocyclic organic bases have been determined in non-aqueous solvents such as acetonitrile [14,16], benzonitrile [18], propylene carbonate [10], nitromethane [11], acetone [8,17], cyclohexanone [8], methanol [9], N 0 ,N 0 -dimethylformamide [11,13], dimethyl sulfoxide [12,13], as well as in the mixed solvents [15].…”

A potentiometric study of (acid + base) equilibria in substituted 4-nitropyridine N-oxide systems in methanol and dimethyl sulfoxide

“…Equation (2) shows that the cationic homoconjugation reactions create symmetric complex ions, [BHB] + , whereas as seen from equation (3) cationic heteroconjugation is a reaction in which a cationic acid BH + reacts with base B 1 conjugated with an acid other than BH + to afford a hydrogen-bonded cations, [BHB 1 ] + . A number of studies of (acid + base) equilibria in nonaqueous solvents were carried out at our laboratory using polar aprotic solvents with diverse polarity and donor properties, such as acetone [1,2], acetonitrile [1,3], benzonitrile [1,4,5], propylene carbonate [1,6], nitromethane [1,7,8], N 0 ,N 0 -dimethylformamide (DMF) [1,8], dimethyl sulfoxide (DMSO) [1,9,10], as well as in the selected amphiprotic solvent, methanol [1,2,11]. In these investigations we revealed that the acidity constants (pK a ) obtained in non-aqueous solvents are linearly correlated with the pK a values in water [11].…”