Nonpolar organic compounds, reaction with

The process employs the supercritical fluid carbon dioxide as a solvent. When a compound (in this case carbon dioxide) is subjected to temperatures and pressures above its critical point (31°C, 7.4 MPa, respectively), it exhibits properties that differ from both the liquid and vapor phases. Polar bonding between molecules essentially stops. Some organic compounds that are normally insoluble become completely soluble (miscible in all proportions) in supercritical fluids. Supercritical carbon dioxide sustains combustion and oxidation reactions because it mixes well with oxygen and with nonpolar organic compounds. 

Although ethers are relatively inert toward reaction, they usually show good solvent properties for many nonpolar organic compounds. This strong dissolving power coupled with low reactivity makes ethers good solvents in which to run reactions. 

Figure 2. Micellar catalysis a, reaction of a water-soluble ion with a nonpolar organic compound and b, reaction of a water-soluble ion with a polar organic compound. Key , ion aaws, nonpolar organic reactant and polar...

Zeolites are clays with rather large internal pore structures which have the property of concentrating nonpolar organic compounds within their cavities. Measurements of gaseous hydrocarbon equilibria have shown enhancements of several orders of magnitude within zeolite pores relative to the vapor phase. Cyclodimerization of butadiene to 4-vinylcyclohexene (Equation 7.5) at 250°C was catalyzed by large-pore zeolites in the sodium form (Dessau, 1986). Zeolites in the Cu(I) form also promoted Diels-Alder addition of furan and other dienes with electron-deficient dienophiles such as methyl vinyl ketone (Equation 7.6). Dichloro-methane was the solvent in these reactions, which usually were carried out at 0°C or lower (Ipaktschi, 1986). 

Both polar and nonpolar organic compounds exhibit a rich chemistry with bare transition metal ions(l). Small polar compounds react with ions such as Fe and Co , in a single, bimolecular step to form a metal-olefin complex, reaction (i). 

In the case of reactions of anionic reagents with nonpolar organic compounds this is often a difficult task since sources of anions - corresponding sodium or potassium salts are soluble only in higly polar, preferentially protic, solvents. On the other hand these solvents are usually unsuitable for nonpolar compounds. Furthermore they interact strongly with anions affecting unfavourably the course of the reactions. 

The previous chapters have demonstrated that liquid-liquid extraction is a mass transfer unit operation involving two liquid phases, the raffinate and the extract phase, which have very small mutual solubihty. Let us assume that the raffinate phase is wastewater from a coke plant polluted with phenol. To separate the phenol from the water, there must be close contact with the extract phase, toluene in this case. Water and toluene are not mutually soluble, but toluene is a better solvent for phenol and can extract it from water. Thus, toluene and phenol together are the extract phase. If the solvent reacts with the extracted substance during the extraction, the whole process is called reactive extraction. The reaction is usually used to alter the properties of inorganic cations and anions so they can be extracted from an aqueous solution into the nonpolar organic phase. The mechanisms for these reactions involve ion pah-formation, solvation of an ionic compound, or formation of covalent metal-extractant complexes (see Chapters 3 and 4). Often formation of these new species is a slow process and, in many cases, it is not possible to use columns for this type of extraction mixer-settlers are used instead (Chapter 8). 

Sodium or potassium ions can also participate in the phase-transfer process when they are converted to lipophilic cations by complexation or by strong specific solvation. A variety of neutral organic compounds are able to form reasonably stable complexes with K+ or Na + and can act as catalysts in typical phase-transfer processes. Such compounds include monocyclic polyethers, or crown ethers (1), and bicyclic aminopolyethers (cryptates) (2). They can solubilize inorganic salts in nonpolar solvents and are particularly recommended for reactions of naked anions. Applications of these compounds have been studied.12,21-31... 

A major use of ethers in the organic laboratory is as solvents for reactions. Ethers are nonpolar enough to dissolve many organic compounds, and the electrons on the oxygen can interact with alkali metal cations to help solubilize salts. In addition, ethers are nonacidic and are not very reactive. For these reasons they are especially useful in reactions involving strongly basic reagents. In addition to diethyl ether, other ethers that are commonly used as solvents are 1.2-dimethoxyethane (DME) and the cyclic ethers tetrahydrofuran (THF) and 1,4-dioxane ... 

Although electrolytes normally do not exhibit significant solubility in nonpolar solvents, many metal ions can react with a wide veriety of organic compounds to form species that are soluble in organic eolvenls. Such solubility, which depends on a chemical reaction, provides a basis for separating and concentrating metals that are present as ions in aqueons eolution. 

A remarkable property of crown ethers is that they allow inorganic salts to be dissolved in nonpolar organic solvents, thus permitting many reactions to be carried out in nonpolar solvents that otherwise would not be able to take place. For example, the Sn2 reaction of 1-bromohexane with acetate ion poses a problem because potassium acetate is an ionic compound that is soluble only in water, whereas the alkyl halide is insoluble in water. In addition, acetate ion is an extremely poor nucleophile. 

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