Acidity, pure aqueous solutions

G. Kortum, W. Vogel, and K. Andrussow, Dissociation Constants of Organic Acids in Aqueous Solution, International Union of Pure and Applied Chemistry, Butterworths, London, 1961. 

The lifetimes of the 9 main thymidine hydroperoxides 5-7 that were determined in pure aqueous solutions at 37 °C were found to vary from 1 h for the two trans diastereomers of 6-hydroperoxides (Table 1) to several weeks for 5-(hydroperoxymethyl)-2 -deoxyuridine. It may be added that the cis diastereomers are more stable than the trans homologues, irrespective of the pair of diastereomeric hydroperoxides. Interestingly, at neutral or slightly acidic pH values a specific hydrolytic decomposition pathway was observed for the two classes of hydroxyhydroperoxides. Thus, it was found that the trans and... 

Rubidium acid salts are usually prepared from rubidium carbonate or hydroxide and the appropriate acid in aqueous solution, followed by precipitation of the crystals or evaporation to dryness. Rubidium sulfate is also prepared by the addition of a hot solution of barium hydroxide to a boiling solution of rubidium alum until all the aluminum is precipitated. The pH of the solution is 7.6 when the reaction is complete. Aluminum hydroxide and barium sulfate are removed by filtration, and rubidium sulfate is obtained by concentration and crystallization from the filtrate. Rubidium aluminum sulfate dodecahydrate [7488-54-2] (alum), RbA SO 12H20, is formed by sulfuric acid leaching of lepidolite ore. Rubidium alum is more soluble than cesium alum and less soluble than the other alkali alums. Fractional crystallization of Rb alum removes K, Na, and Li values, but concentrates the cesium value. Rubidium hydroxide, RbOH, is prepared by the reaction of rubidium sulfate and barium hydroxide in solution. The insoluble barium sulfate is removed by filtration. The solution of rubidium hydroxide can be evaporated partially in pure nickel or silver containers. Rubidium hydroxide is usually supplied as a 50% aqueous solution. Rubidium carbonate, Rb2C03, is readily formed by bubbling carbon dioxide through a solution of rubidium hydroxide, followed by evaporation to dryness in a fluorocarbon container. Other rubidium compounds can be formed in the laboratory by means of anion-exchange techniques. Table 4 lists some properties of common rubidium compounds. 

By treating the crude solution of perdisulphuric acid with the requisite quantity of barium carbonate or hydroxide, the unaltered sulphuric acid can be removed and a pure aqueous solution of pcrdi-sulphuric acid obtained.4... 

Hydrogen peroxide exhibits a weak acidic character, having a dissociation constant of about 1.5 x 10 l2 thus, pure aqueous solutions of hydrogen peroxide have pH values below 7. The dissociation constant of hydrogen peroxide is 10 ... 

Perbromic acid is a strong monobasic acid. Its aqueous solutions are stable up to about 6 M (55% HBr04), even at 100°. Fairly concentrated solutions may develop a yellow bromine color from the decomposition of traces of bromate ion and hypobromous acid. If a 6 M perbromic acid solution is allowed to stand for several months, the bromate and hypobromite will have all decomposed, and the resulting bromine can be flushed out with pure nitrogen, leaving a colorless solution. 

Hydrogen chloride is produced industrially on a huge scale and is used as the anhydrous gas as well as a hydrochloric acid in aqueous solution. Several industrial routes to synthesize HCl are in use (1) direct burning of hydrogen in chlorine, which results in a very pure product (equation 85) (2) reaction of an inorganic metal halide with a less volatile protic acid, such as sulfuric acid, to form the more volatile hydrogen halide (equation 86) and (3) as a by-product of the chlorination of hydrocarbons (equation 87). 

Trifluoroacetic acid is a nonoxidizing acid whose aqueous solutions are comparable in strength with those of the mineral acids 115), but as a bulk solvent it is weakly acidic and does not even protonate water (236). Trifluoroacetic acid is also weakly basic and is a nonelectrolyte in 100% sulfuric acid (21). One of the major difficulties of using pure trifluoroacetic acid is its remarkable affinity for water and, to maintain an anhydrous medium, a small quantity of trifluoroacetic anhydride is usually added. This affinity for water is so pronounced that trifluoroacetic acid will dehydrate oxyacids and, for example, converts sulfuric acid into polysulfuric acid. 

An aqueous solution of sulfuric acid and a salt of periodic acid, trisodium paraperiodate, or one of the potassium periodates, has been used frequently as a substitute for pure periodic acid. When the product of the oxidation reaction is to be isolated, the effect of the presence of metal ions on the yield should be considered. If the product is volatile or slightly soluble, or is isolated either as a slightly soluble derivative or by extraction with organic solvents, the presence of metal ions should not reduce the yield. In the case of certain methylhexosides which were oxidized by periodic acid formed from potassium metaperiodate and an equivalent of sulfuric acid in aqueous solution, the presence of potassium ions was found to cause a low yield of the crystalline strontium salt prepared by the strontium hypobromite oxidation of the dialdehyde resulting from the periodic add reaction. Oxidation by pure periodic add, a solution of which is prepared either from crystalline parapeiiodic add or by the previously mentioned method from potassium metapeiiodate, is desirable when the presence of difficultly removed metal ions affects the yield adversely. 

Glycolic acid is extremely hydrophilic, and a pure aqueous solution of glycolic acid, saturated at a concentration of about 80%, has a pH of 0.5. This pH, considerably lower than its pK, of 3.83, shows that the solution consists mostly of pure acid and is effective for performing a peel. The pH of a glycolic acid solution determines its acidifying power on the skin a 3% glycolic acid solution at pH 3 can acidify the first five layers of corneocytes, whereas at 10% and pH 3, it causes a deeper and more rapid acidification of the... 

This product is pure enough for use in preparing boron trifluoride. If a clean, pure preparation of ammonium fluoborate is required for another purpose, the best way to make it is to mix the theoretical amounts of ammonium acid fluoride and boric acid in aqueous solution in a plastic dish, and evaporate to crystallization on a steam bath. ... 

Selenic acid is said to be the only acid which in pure aqueous solution will attack gold. Perform experiments to see if it will attack, gold leaf. 

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