Compounds from aqueous solutions solubility

In the isolation of organic compounds from aqueous solutions, use is frequently made of the fact that the solubility of many organic substances in water is considerably decreased by the presence of dissolved inorganic salts (sodium chloride, calcium chloride, ammonium sulphate, etc.). This is the so-called salting-out effect. A further advantage is that the solubility of partially miscible organic solvents, such as ether, is considerably less in the salt solution, thus reducing the loss of solvent in extractions. 

Another method of removing mercury compounds from aqueous solution is to treat them with water-soluble reducing agents, thus hberating metallic mercury (26). The use of formaldehyde (qv) at a pH of 10—12 also is recommended. 

Figure 11.6 Sorption isotherms for two kinds of nonionic organic compounds from aqueous solutions to suspended kaolinite (a) slightly monopolar compound, pyrene, showing a linear isotherm up to its solubility (Backhus, 1990), and (b) monopolar compound, 1,3,5-trinitrobenzene, showing a hyperbolic isotherm (Had-erlein et al., 1996).

Supercritical fluids such as carbon dioxide can be used as solvents to extract organic compounds from aqueous solutions. In order to achieve recoveries of these products often in low concentration, cosolvents as methanol or other alcohols have been added to improve the solubility and the selectivity of the primary fluid. To optimize the extract recovery, the knowledge of phase equilibria of the ternary system carbon dioxide-methanol-water is required at different temperatures and pressures. 

For illustration, rubbery polymeric membranes, whose polymeric network is sufficiently elastic and mobile to allow comparatively large organic compounds to diffuse through it (Table 3.6-2), are in general used for the recovery of organic compounds from aqueous solutions. Because of its small size, the bulk solvent, water, unfortunately diffuses through the membrane even better. This is why in organo-philic pervaporation the selectivity is mainly achieved and determined by the ratio of the solubility coefficients (sorption selectivity. Table 3.6-2). Membrane selectivity, as defined in Eq. (7), is an intrinsic parameter and can differ from the overall process selectivity, as wiU be shown later. 

The surfaces of the resins are highly aromatic. Sizable fractions of the surfaces are benzene rings (Albright, 1986). For this reason, the unfunctionalized polymeric resins are hydrophobic. The ion exchange resins are, however, not hydrophobic. The hydrophobic resins need to be pretreated to become wetted prior to use in water treatment. The pretreatment involves immersion in a water-soluble solvent, such as acetone or methanol, to displace air from the pores, followed by displacement of the solvent by water or aqueous solution. The aromatic surfaces of the resins make them excellent sorbents for removal of organic compounds from aqueous solution, particularly those with low solubilities. 

Nonpolar compounds (from aqueous solutions and soluble in hexane, heptane and chloroform)... 

The constant K is termed the distribution or partition coefficient. As a very rough approximation the distribution coefficient may be assumed equal to the ratio of the solubilities in the two solvents. Organic compounds are usually relatively more soluble in organic solvents than in water, hence they may be extracted from aqueous solutions. If electrolytes, e.g., sodium chloride, are added to the aqueous solution, the solubility of the organic substance is lowered, i.e., it will be salted out this will assist the extraction of the organic compound. 

Many of the heavy metal xanthates have been piepaied from aqueous solutions of the alkah metal xanthates and the water-soluble compound of the heavy metal desired. 

In general, the tetracyclines are yellow crystalline compounds that have amphoteric properties (Fig. 2) (15). They are soluble in both aqueous acid and aqueous base. The acid salts tend to be soluble in organic solvents such as 1-butanol, dioxane, and 2-ethoxyethanol In fact, 1-butanol is used to extract the salts from aqueous solution. 

Beryllium fluoride is hygroscopic and highly soluble in water, although its dissolution rate is slow. FluoroberyUates can be readily prepared by crystallization or precipitation from aqueous solution. Compounds containing the BeP ion are the most readily obtained, though compounds containing other fluoroberyUate ions can also be obtained, eg, NH BeF, depending upon conditions. 

These compounds are odourless, rather unstable compounds, and should be distilled under vacuum in an inert atmosphere. They are water-soluble but can be extracted from aqueous solution with a solvent such as diethyl ether. 

Functional organosilanes can be applied to substrates directly from aqueous solutions, provided the silane compound is soluble is water. 

Environmental chemicals occur as pure liquid or solid compounds, dissolved in water or in nonaqueous liquids, volatilised in gases, dissolved in solids (absorbed) or bound to interfaces (adsorbed). Figure 5 gives a schematic view of the different physical states at which substrates are taken up by microbial cells. There is a consensus that water-dissolved chemicals are available to microbes. This is obvious for readily soluble chemicals, but there is also clear evidence for microbial uptake of the small dissolved fractions of poorly water soluble compounds. Rogoff already had shown in 1962 that bacteria take up phenanthrene from aqueous solution [55], In the intervening time many other researchers have made the same observation with various combinations of microorganisms and poorly soluble compounds [14,56,57]. 

The structure of [H2Wi2O42]10 (paratungstate B) has been determined in at least eight different compounds (Fig. 20). This polyanion is not very soluble and is easily crystallized from aqueous solutions at pH 6-7 with cations such as Na+, K+, NH4, and Mg2+ (158). The role of hydrated cations in the stabilization and crystallization of this polyanion has been discussed (159). The position of the protons has been located by neutron diffraction as internally bound (159, 160) as predicted on the basis of crystallographic work (158b). 

The logarithm of the solubility product for hydroxyapatite is -58.6 and that of fluorapatite (CajtPO jF) is -60.6 (57), and thus, D = 0.01 in favour of fluoride incorporation into the solid apatite precipitate. Accordingly, it should be difficult to prepare solid solutions of these compounds by precipitation from aqueous solution and if prepared batchwise, they are expected to contain logarithmic gradients in their internal composition. Yet, Moreno et al.(M3) report linear changes in the lattice parameters of such solid solutions. They also determined their solubility behavior. 

The hexammino-salts are yellow or brownish compounds, easily crystallised and fairly stable. They withstand the action of boiling water for some time, and can therefore be crystallised from aqueous solution if crystallisation be carried out quickly. Acid solutions of the salts are very stable, but alkaline and neutral solutions are decomposed on heating. The salts are more soluble than the corresponding aquo-pentammino-salts, and their solutions are brownish yellow in colour. The hydrated salts effloresce in air and become opaque and reddish brown in colour. On heating they lose ammonia, leaving eobaltic oxide and a cobaltous salt. In cold solution they give no precipitate with sodium hydroxide, ammonium hydroxide, or alkali... 

The sulphato-derivative, [Pd(NH3)2S04], crystallises in orange-yellow octahedra, is soluble in cold water, and is precipitated from aqueous solution by hydrochloric acid. It is obtained by treating the hydroxo-compound with sulphuric acid, or by the double decomposition of the chloride with silver sulphate.2... 

The compound Re(CO)5(FBF3) is soluble in water to give a solution of [Re(CO)5(OH2)]+. A series of water insoluble neutral pentacarbonylrhenium derivatives has been obtained from aqueous solutions of pentacarbonyl-(tetrafluoroborato)rhenium and various salts12 ... 

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