Basicity of N-substituted anilines and pyridine in dimethylsulfoxide

Abstract

. Can. J. Chem. 59, 1501Chem. 59, (1981.The ionization constants of the conjugated acids BH+ of aniline, N-methyl-and N,N-dimethylaniline, and pyridine have been determined potentiometrically in MeZSO. The heats of neutralization of the amines B and their heats of solution have been obtained by calorimetry. The pK's and enthalpies of ionization of these BH+ ions and alkylammonium ions are linearly related. Comparisons with gas phase data show that the abnormal basicity order of the amines B in Me,SO is mainly due to the decreasing exothermicity of the heat of solution of the BH+ ions with the number of N-H protons available for H-bonding to Me,SO. The large increase in basicity difference between equally substituted aromatic and alkylamines, when passing from the gas phase to Me,SO, is linked to the larger heat of vaporization of the aromatic amines. While the acid-base properties of compounds (+NMe2), and pyridine (Py). Potentiometric and belonging to related series often follow a rational calorimetric determinations were carried out to sequence in the gas phase, the sequence can be provide the necessary data in Me2S0 and some complex when the compounds are present as sol-supplementary data in water and CCl,. utes. The modifications in the basicity of alExperimental kylamines B according to the nature and number of Materials a l k~l substituents is a case in point 9 2).Me,SO (BDH) was reagent grade. It was dried (water content example, in the gas phase the basicity order is less than 0.02%) and stored over 4A molecular sieves. Aniline (Anachemia), N,N-dimethylaniline (Fisher Scientific), and Me3N > > n-PrNH2> EtNH2 > MeNH2 > NH3 pyridine (BDH, 99.5% purity) were reagent grade and used while in the solvent dimethylsulfoxide ( M~~s o ) the without further purification. N-Methylaniline (Eastman Kodak practical grade) was distilled under reduced pressure and the order becomes middle fraction used. Trifluoromethanesulfonic acid (3M MeNH, -E~NH, > n-PrNH2 > NH, -Me2NH > Me,N Chemical) was used as received, as were tetraethylammonium iodide (Baker reagent grade) after drying 12 hat 50°C and tetrathus NH3 is more basic than Me3N by 2.0 pK units. ethylammonium perchlorate (Eastman reagent) after similar Then in water, the sequence changes to drying.Potentiometric titrations of Me,SO solutions of the amines ( 2 SO that NH3 is now a weaker base than Me3N with a x lo-) to 1 x 10-2M) with standardized solutionsof HCF,SO, in 0.6 pK difference. Comparison of amines protons-Me2S0 were carried out in a glove box under a stream of dry nitrogen. The solution in the cell was maintained at 25.0°C by data in and in the gas-phase provides a means of a jacket through which temperature-controlled water llnderstanding the effect and circulated. The electrodes used were a glass electrode some interesting Variations in the ~0lVati0n of both (Radiometer G202B) which was calibrated twice with standard B and BH+. We have recently reported such HCF,S03 to give a 62.4 f 0.3 mV slope (intercept: 85.76 f a comparison (2) and we present here th...

Solvent effect on preferred protonation sites in nicotinate and isonicotinate anions

“…Extrapolation of the pKa values that we measured over the range 0-95% Me2S0 to pure Me2S0 (see Fig. 1) leads, however, to a pK,Me2SO value in good agreement with that directly determined by Benoit et al in this solvent (24).…”

Basicity of 1,8-bis(dimethylamino)naphthalene and 1,4-diazabicyclo[2.2.2]octane in water and dimethylsulfoxide

“…Our values of the enthalpies of transfer A e of PS, DABCO, PSH+, and DABCOH+ from water to Me2S0 (Table 4) present interesting results when compared with previous data (18,21) for aliphatic and aromatic amines. First, the small A e for PS is typical of what is observed for aromatics1 (for C6H6, AH: = -0.3 kJ mol-') so that, given the high negative value of A@, there must be a very large compensating positive entropy of transfer, as is common to aromatics, and which reflects the peculiarities of water as a solvent.…”

“…1 and the dissociation constant of water at 0.11 ionic strength. The pK, for PSH;' was obtained from the 13c nmr data in [10][11][12][13][14][15][16][17][18] M H2S04 by using the excess acidity method and the program developed by Cox as previously described (1 1 The free energy of transfer A@ (hypothetical 1 M solution as standard state) from water to Me2S0 for both PS and DABCO was obtained from the partition coefficient PSI, calculated in turn from the partition coefficient between Me2S0 and n-heptane, Phis, and the partition coefficient, Phlw, between water and n-heptane. For PS, we determined Phlw from the experimental relation between the distribution coefficient D and pH, log D = 6.…”

<b>Determination of protonation constants of some 3-alkyl(aryl)-4-(<i>p</i>-t-butyl(benzyl/benzyliden)amino)-4,5-dihydro-1<i>H</i>-1,2,4-triazole-5-one derivatives in ethanol–water mixtures</b>

“…In this study, six compounds (1-6) which are derivatives of 3-alkyl(aryl)-4-(p-tbutylbenzylidenamino)-4,5-dihydro-1H-1,2,4-triazole-5-one and six compounds (7)(8)(9)(10)(11)(12) which are derivatives of 3-alkyl(aryl)-4-(p-t-butylbenzylamino)-4,5-dihydro-1H-1,2,4-triazole-5-one were titrated potentiometrically in 50% (v/v) ethanol-water mixtures. The mV values, which were read from pH meter, were plotted versus sodium hydroxide volumes (mL) added and thus potentiometric titration curves were formed for all the cases (Figure 2-5).…”

“…There have been a number of systematic studies of the acidity in different media using different techniques [1][2][3][4][5][6][7][8][9][10][11][12][13], but unfortunately very few have dealt with triazoles. It is well known that two major factors influence the acidity of a molecule [14][15][16][17], namely, structural and solvent effects.…”