Edward M. Arnett

Protonation and Solvation in Strong Aqueous Acids

Publisher Summary This chapter discusses protonation and solvation in strong aqueous acids. The present status of the determination of pK and acidity functions for individual bases in terms of the Bunnett–Olsen equation is discussed. The available measured and derived thermodynamic data for the protonation of important representative bases in aqueous acids, superacids, and the gas phase is tabulated. The chapter explains how these data may be used to estimate the ionization ratios of the different bases in aqueous acid media, including their pK -values in water at different temperatures. The solvation energies of the onium ions of the protonated bases are estimated. The acidity function and hydration behavior of the different classes of bases are related and the data for a practical theory of acidity functions are discussed.

The hydration of anions in nonaqueous media

A very simple isopiestic method based on that of S. Christian is used for measuring the salting-in of water into nonpolar, low-volatility solvents by tetraalkylammonium salts. The quantity of excess water which is dissolved in such solvents is directly proportional to the salt concentration and is sharply dependent on the nature of the anion but is nearly insensitive to that of the R4N+ cation. The hydration ratioH, which we define as the moles of excess solubilized water per mole of R4N+ X−, is directly relatable to the enthalpy of hydration of the anion X− in several solvents and in the gas phase. The quantityH is also correlated with many free-energy terms including those for the Hofmeister lyotropic series, for the ability of the anions to salt nonelectrolytes out of water, for the free-energy terms for separation of these ions by reverse osmosis membranes, and for their nucleophilicities. A surprising (but not unprecedented) feature of the hydration ratio is that it, rather than its logarithm, behaves as a free-energy term. It is proposed that all these properties have in common the free energy of hydration of the anions, and this notion is supported by a close correspondence between the anionic hydration ratio and their hydrogen-bonding energies with proton donors in aprotic solvents. The results support scattered observations by other workers that isolated water molecules do not have an unusual inherent affinity for anions. Accordingly, large anionic hydration energies in bulk aqueous media reflect extensive cooperative interactions in the solvent. Implications for nucleophilic activity in phase transfer catalysis and enzyme activity are mentioned.

Thermochemical comparison of deprotonation in KAPA (potassium 3-aminopropanamide) and potassium DMSYL

Abstract Heats of deprotonation in solutions of the potassium salt of 1,3-diaminopropane in the parent amine as solvent indicate that it is over a million times more basic than the potassium salt of DMSO.

Deuterium Analysis— a Simple and Precise Method

By means of reaction with calcium hydride in a generator of simple design, the water samples are converted into H2 and HD. With hydrogen as carrier gas, the greater thermal conductivity of HD produces a peak whose size is linearly related to the deuterium content of the original water.