The solubilities of organic compounds

A compound is most soluble in that solvent to which it is most closely relaM in structure. Thus w-hexane, which is sparingly soluble in water, dissolves in three volumes of methyl alcohol, is more soluble in anhydrous ethyl ilcohol, and is completely miscible with n-butyl and higher alcohols. As the chain length increases the compound tends to resemble the hydrocarbon more and more, and hence the solubility increases. 

The effect of a halogen atom or of phenyl is analogous to an increase in ie nurrher of carbon atoms. 

The lower members of othOT homologous series of oxygen compounds— the acids, aldehydes, ketones, anhydrides, ethers and esters—have approximately the same limits of solubility as the alcohols and substitution and branching of the carbon chain has a similar influence. For the amines (primary, secondary and tertiary), the limit of solubility is about C whiM for the amides and nitriles it is about C4. 

Compounds of very high molecular weight frequently exhibit decreased solubility in inert solvents. Thus whilst glucose (C HioOt) and methyl 

An interesting illustration is urea CO(NH2)2, m.p. 132°, which is very soluble in water, and oxsmide (CONH2)2. m-P- 420°, which is sparingly soluble in water. 

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Non-aqueous microemulsions have been prepared by replacing water with formamide, a highly structured polar solvent [71]. Formamide enhances the solubility of organic compounds and is also used as a reactant. 

Metal ions in aqueous solution exist as complexes with water. The solubility of organic compounds in water depends primarily on their polarity and their ability to form hydrogen bonds with water. Organic compounds with a large part of polar components such as acetic acid, dissolve in water without limit. In such cases, the polar part dominates. By contrast, soaps and detergents have a polar end attached to a relatively large nonpolar part of the molecule. They have limited solubility and the molecules tend to coalesce to form micelles. 

Palit, S.R. Electronic interpretations of organic chemistry. II. Interpretation of the solubility of organic compounds, J. Phys. C/tem, 51(3) 837-857, 1947. 

Effects of electrolytes on the solubility of organic compounds in aqueous solutions were established empirically more than 100 years ago by Setschenow (1889). He found that the presence of dissolved inorganic salts in an aqueous solution decreases the aqueous solubility of nonpolar and weak polar organic compounds. This effect, known as the salting-out effect, is expressed by the empirical Setschenow formula... 

Table 6.3 Effects of salts on the solubility of selected organic compounds expressed as Setschnow constant (L/mol). Reprinted from Xie WH, Shin WY, Mackay DA (1997) Review of the effect of salts on the solubility of organic compounds in seawater. Marine Envir Res 44 429-444. Copyright 1997 with permission of Elsevier...

The solubilities of organic compounds such as alkanes, cycloalkanes, alkenes, aromatic hydrocarbons, saturated alkylamines, and N- and S-containing aromatic compounds in several ionic liquids were reported recently (86). The solubilities in the ionic liquid [TMAC]Al2Cl7 are listed in Table IV. 

However, it may also be possible that the buffer negatively influences the solubility of the drug and other excipients. Buffer salts can either increase or decrease the solubility of organic compounds in water. The effect depends on a combination of the polarity of the solute and of the salt. Nonpolar solutes are solubilized (salted in) by less polar organic salts and are desolubilized (salted out) by polar salts. Conversely, polar solutes are salted in by polar salts and salted out by organic salts. It was shown that for a semipolar solute such as ampicillin, strong electrolytes... 

Chiou, C. T. Kile, D. E. (1994). Effects of polar and nonpolar groups on the solubility of organic compounds in soil organic matter. Environmental Science Technology, 28,1139—44. 

An emulsifier is a molecule that possesses both polar and nonpolar moieties, i.e., it is amphiphilic. In very dilute water solutions, emulsifiers dissolve and exist as monomers, but when their concentration exceeds a certain minimum, the so-called critical micelle concentration (CMC), they associate spontaneously to form aggregates - micelles. Micelles are responsible for many of the processes such as enhancement of the solubility of organic compounds in water, catalysis of many reactions, alteration of reaction pathways, rates and equilibria, reaction loci for the production of polymers, etc. 

Grant and Higuchi (1990) commented on the solution behavior of solvates in their book on the solubility of organic compounds. The hydrated form will be more stable (less soluble) than the anhydrate in the general case. When the solvate is formed from a nonaqueous solvent that is miscibli in water, the free energy of solution of the solvent into the water reduces the activity of water and increases the apparent solubility of the solvate. An example is cited in which caffeine hydrate is less soluble in water than the anhydrate, but the solubility order reverses in ethanol. 

Surfactant A substance that reduces surface tension of the liquid used to dissolve it and increase the solubility of organic compounds. Found in herbicides. 

Goydan. R Reid, R.C., Tseng, H. Estimation of the solubilities of organic compounds in polymers by group-contribution methods. Ind. Eng. Chem. Res., 1989.28 445-454. 

The solubility of inorganic compounds, such as e.g. salts, decreases in the same way as the solubility of organic compounds in the supercritical state increases. This decrease is combined with the decrease of the dielectric constant of water. The supercritical water oxidation process is described in the following figure. 

While the solubility of organic compounds, the inert gases and such are dealt with in Chapter V, let us here discuss the solubility of the typical ionic lattices. 

The choice of the anion is most important in anodic reactions. Perchlorates have been found very useful as they are difficult to oxidize and are often soluble both in water and nonaqueous solvents. In anodic (Section VI, F) or cathodic (Section IV, A) substitution reactions the nucleophilicity of the anion is of interest. High concentrations of tetraalkylammonium p-toluenesulfonates in water make the solubility of organic compounds higher than in pure water, and such solutions combine a low ohmic resistance with good dissolving power. 

Solubility is commonly defined as the concentration of dissolved solute in a solvent in equilibrium with undissolved solute at a specified temperature and pressure. For a deeper and more detailed understanding of the diverse rules determining the solubility of organic compounds in various solvents, see references [312-316],... 

Generally liquid ammonia is a good solvent for many salts, such as nitrates, nitrites, iodides, cyanides, thiocyanides, and acetates. Ammonium salts are especially soluble. The hydroxides, fluorides, and salts with di- and trivalent anions, such as oxides and sulfides, in general are insoluble. Apart from alkali metals, some other metals and nonmetals are also soluble. A compilation of the solubilities of organic compounds in liquid ammonia shows notable solubility of saccharoses [1417],... 

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