. 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...

The transition state partial molal volume behavior, rt, as a function of binary solvent composition was obtained for three reactjons b l dissection of the activation volume, AV*, into initial and transition state components: AV* = V , -Vg. The solvolyses of t-butyl chloride, benzylchloride, andp-chlorobenzyl chloride represented a gradation of reaction type between SNI and SN2 and the transition state partial molal volume behavior was found to be distinctly different in each case and in agreement with the mechanistic classification of these reactions.

The temperature dependence of the transition state volume, d V ' / d~, in a number of hydrolysis reactions derived from pressurehate data and partial volume temperature dependence. The values obtained for dVt/dT vary from near zero forp-methylbenzyl chloride to about 0.3 ml mol-I deg-I for isopropyl bromide. The interpretation of the experimental and derived values for these hydrolyses is discussed in terms of charge development with accompanying solvation effects about the solute.La dependance du volume de I'ttat de transition de la temptrature dVt/dT, dans un nombre de rkactions d'hydrolyse provient de la pression/vitesse donnte et de la dependance de la temperature du volume partiel. Les valeurs obtenues pour dVt/dT varient pres de zero pour le chlorure de p-methylbenzyle a environ 0.3 ml mol-I deg-I pour le bromure d'isopropyle. L'interpretation de ces donnees experimentales pour ces hydrolyses est discutte en terme de developpement de charge accompagnant 1es effets de solvatation autour du solute.

Various equations which have been proposed to provide the 'best' functional form for the dependence of rate upon pressure for reactions in solution have been tested for the extraction of ΔV≠ and dΔV≠/dp for the hydrolysis of benzyl chloride at 30 °C and at pressures over the range 1 to 6895 bar. One hundred individual rate constants were determined for this reaction at pressure increments of 345 bar and provide a sufficiently large body of data to permit application of statistical methods for testing the various rate–pressure functions with little risk of bias.