Oxygen containing compounds, protons

Ruelle, P., Kesselring, U. W., Prediction of the aqueous solubility of proton-acceptor oxygen-containing compounds by the mobile order solubility model, J. Chem. Soc.,... 

It has been known since the turn of the century that amongst oxygen-containing compounds crystalline salts with protonic acids are most readily formed by 2,6-dimethyl-4-pyrone [190] (Collie and... 

These species, for oxygen-containing compounds, have a large stability (in excess of 20 kcal mol - ) and require a very loose association. This stability allows for partial proton transfer to the alcohol, even when the ester has a larger proton affinity than the alcohol. The scheme is also consistent with the picture that reactions will take place only at centres prone to form a carbenium ion, namely secondary or tertiary carbon centres. 

If the unknown, neutral, oxygen-containing compound does not give the class reactions for aldehydes, ketones, esters and anhydrides, it is probably either an alcohol or an ether. Alcohols are readily identified by the intense characteristic hydroxyl adsorption which occurs as a broad band in the infrared spectrum at 3600-3300 cm-1 (O—H str.). In the nuclear magnetic resonance spectrum, the adsorption by the proton in the hydroxyl group gives rise to a broad peak the chemical shift of which is rather variable the peak disappears on deuteration. 

In the example HCl + H20 —> H301+ + Cl1-, which substance is the acid and which is the base Look at the compound that contains chlorine. As a reactant the chlorine has one proton, but as a product the chlorine is an ion by itself. The chlorine compound has lost a proton and the HCl can be labeled as an acid. The water, or oxygen-containing compound, has two hydrogen atoms as a reactant but now has three hydrogen atoms/ions as a product. Therefore, the water is labeled as a base. (See Figure 9.1.)... 

Steps 3 and 4. These steps are equilibria in which oxygens lose or gain a proton. Such acid-base equilibria are reversible and rapid and go on constantly in any acidic solution of an oxygen-containing compound. In step 4, it does not matter which —OH group is protonated since these groups are equivalent. 

OXONIUM COMPOUNDS. Coordination compounds, commonly of certain oxygen-containing organic substances, with mineral acids, of the general type [R 0]HCI. These compounds bear a strong resemblance to the oxonium (hydronium) ion, which is a proton in combination with a water molecule, and is the form in which protons commonly exist in aqueous solutions. 

Metal oxygen cluster compounds with keggin structure have received attention as acid catalysts for several acid catalysed reactions in the liquid as well as in vapour phase conditions [1-6]. Studies on a series of salts with monovalent cations and various heteropolyanions have revealed that certain of these solids in particular those containing potassium, cesium,ammonium and thallium cations possess microporous structure [7-11]. Photoacoustic FTIR investigations and the studies on the chemisorption of ammonia and pyridine have shown that residual protons remain and these protons are responsible for the catalytic activity[12,13]. 

---