Nonpolar aprotic solvent

Crown Ethers Nucleophilic Substitution Reactions in Relatively Nonpolar Aprotic Solvents by Phase-Transfer Catalysis... 

In some ways the ideal solvent for an Sn2 reaction would be a nonpolar aprotic solvent such as a hydrocarbon or a relatively nonpolar chlorinated hydrocarbon. 

A term, usually referring to a solvent, describing a compound which act neither as a proton donor nor a proton acceptor. Examples of polar aprotic solvents include dimethylformamide, dimethylsulfoxide, acetone, acetonitrile, sulfur dioxide, and hexamethylphosphoramide. Examples of nonpolar aprotic solvents include benzene and carbon tetrachloride. Studies of reactions in protic and aprotic solvents have demonstrated the importance of solvation on reactants, leaving groups, and transition states. Degrees of nucleophilicity as well as acidity are different in aprotic solvents. For example, small, negatively charged nucleophiles react more readily in polar aprotic solvents. It should also be noted that extremely... 

Eurthermore, it was noted that the product ratio was also dependent on the nature of the solvent employed. Thus, the nitrone 186 (Equation 122) undergoes cyclization in nonpolar aprotic solvents such as benzene or toluene and polar aprotic solvents such as DMSO, DME, or acetonitrile to afford the five-membered ring cycloadduct 155 as the... 

The addition of bromine to alkenes is a rapid, exothermic reaction usually taking place at room temperature. In contrast to chlorination, the rate law in bromination depends on the solvent used. On passing from hydroxylic to nonpolar aprotic solvents, the overall second-order changes to a rate law that is first-order in alkene and second-order in bromine.226 Alkene-bromine complexes with varying compositions were shown to form under reaction conditions3,218,227 228(Scheme 6.5). At low bromine concentration in protic solvents the reaction proceeds via a 1 1 complex (23). A 1 2 alkene-bromine complex (25) is involved at high bromine concentration in nonprotic solvents. The ionic intermediates (24, 26) were shown to exist as contact ion pairs, solvent-separated ions, or dissociated ions. 

Some investigations on the solvent effect concerning the aggregation tendency of surfactant in nonpolar media have been made in mixed solvent systems. These yield information on the relative stability of a particular miceliar structure in one of the solvent components with respect to the other. Also inversion of the micellar structure has been observed in such cases where nonpolar, aprotic solvents were mixed with those giving rise to hydrophilic interactions, i.e., which are in general structure forming. 

Borabenzene anions can serve as n ligands to a thallium(I) center, as demonstrated by the work of Herberich et al. (183). Reaction of alkali metal borinates with thallium(I) chloride yields the pale yellow, sublimable complexes LVIa,b [Eq. (16)] (see Fig. 11), which are only sparingly soluble in nonpolar aprotic solvents but easily soluble in pyridine and dimethylsulfoxide (183). 

The general process begins with Cr(CO)3L3, in which the L unit can be CO (most common),MeCN, " o-alkylpyridine, ammonia, and other donor ligands (equation 91). The rate (reaction temperature) is related to the nature of L the most reactive readily available source of Cr(CO)3 is ( ] -naphthalene)Cr(CO)3, which undergoes favorable arene exchange under mild conditions with many substituted arenes. " The most general and convenient procedure employs a mixture of THF and di-n-butyl ether at reflux. " A variety of polar and nonpolar aprotic solvents has been used and, for some purposes such as complexation of a-amino acids with aromatic side chains, water-THF mixtures are effective. 

In general, polar componnds (e.g., alcohols, thiols, amines, carboxylic acids, amides) tend to dissolve in (polar) protic solvents (e.g., water, alcohols). Nonpolar compounds tend to dissolve in (nonpolar) aprotic solvents (e.g., benzene, petrol, hexane). 

Solubility sol in both polar and nonpolar aprotic solvents like diethyl ether, THF, methylene chloride, pentane, hexane, etc. 

The ease and the stereochemical course of hydrogenation of a,p-unsaturated ketones are particularly influenced by the nature of the solvent and the acidity or basicity of the reaction mixture. Some efforts have been made to rationalize the effect of the various parameters on the relative proportions of 1,2- to 1,4-addition, as well as on the stereochemistry of reduction. For example, the product distribution in -octalone hydrogenation in neutral media is related to the polarity of the solvent if the solvents are divided into aprotic and protic groups. The relative amount of cis- -decalone decreases steadily with decreasing dielectric constant in aprotic solvents, and increases with dielectric constant in protic solvents, as exemplified in Scheme 21 (dielectric constants of the solvents are indicated in parentheses). Similar results were observed in the hydrogenation of cholestenone and of testosterone. In polar aprotic solvents 1,4-addition predominates, whereas in a nonpolar aprotic solvent hydrogenation occurs mainly in the 1,2-addition mode. 

How do we rationalize what appears to be a trimolecular reaction Because the solvent is a nonpolar aprotic solvent, the phosphonium carboxylate must be present as an ion pair and can be considered as a single entity. The carboxylate ion also may be properly situated to remove the proton. 

Hydrogen abstraction by LO to propagate free radical chains is facile also in nonpolar aprotic solvents when lipids are at high concentrations. However, at moderate lipid concentrations, H abstraction must compete with internal rearrangements and scission (304), and at low concentrations it may become insignificant (305). 

Conjugate additions. Efficient reaction between silyl ketene acetals and conjugated carbonyl compounds in nonpolar aprotic solvents (such as toluene, while containing TMEDA) is possible when catalyzed by LiAl[OC(CF3)2Ph]. The catalyst is derived from LiAlH and HOC(CF3)2Ph. 

Finally, in nonpolar aprotic solvents such as benzene or cyclohexane trityl anion formation is possible only with activating agents more powerful than /-BuONa vide infra). 

Modification of the reaction conditions, such as higher temperatures, using different nonpolar aprotic solvents or addition of lithium bromide, iron(III) chloride, hydroquinone, or benzoyl peroxide slightly reduced the yield of the brominated cyclopropane. The bromine at the methyl group can be replaced by hydrogen in high yield using sodium triethylborohydride in... 

Equilibration may also be involved in some of the reactions of acyl-stabilized ylides such as Ph3P=CHC(0)CH3, or of the formyl analogue Ph3P=CHCHO, reagents that tend to produce ( )-alkenes in alcohols or halocarbons as well as in the nonpolar, aprotic solvents. These highly stabilized ylides are not very reactive, and extended reaction times increase the risk of Z/E interconversion. On the other hand, product equilibration has been ruled out for at least some of the E-selective reactions of the relatively reactive a-substituted ylide Ph3P=C(Me)C02R". 

Solubility for X = Cl, sol in H2O, CH3OH, CH3CN, DMF, and DMSO insoluble in nonpolar, aprotic solvents for X = PFg, sol in CH3CN, acetone, DMF, and DMSO insoluble in H2O. Form Supplied in the dichloride is commercially available from Strem Chemicals, Inc. and Sigma-Aldrich as the hexahydrate. [Ru(bpy)3] + complexes appear as red to orange crystals or powder. 

Depending on the modifications of poly-(p-phenylene terephthalamide) and analogous aromatic polyamides, it is possible to vary the solubility from concentrated sulfuric acid, to nonpolar aprotic solvents with inorganic salts, or to nonpolar aprotic solvents and to common organic colvents. In particular the incorporation of noncoplanar 2,2 -disubstitution has proven to remarkable enhance the solubility and lower the crystallinity. Gaudiana et al. [35] demonstrated that para-linked aromatic polyamides containing noncoplanar 2,2 -bis(trifluorome-thyl)biphenylene units are highly soluble in... 

In nonpolar aprotic solvents, such as the aliphatic and aromatic hydrocarbons and symmetrical halogenated hydrocarbons, or in polar solvents, such as aldehydes, ethers, and asymmetric halogenated hydrocarbons, the cathodic process can be the reduction of oxygen, which is quite soluble in hydrocarbons, or the reduction of protons allowed by the presence of halogen acid resulting from the hydrolysis of halogenated hydrocarbons. The polar behavior of the solvent favors the solvating effect of metal ions, the solubilization of the corrosion products of the corrosion process. 

The results obtained are certainly not conclusive they are indicative, however. Although much more data is required for absolute certainty, it seems very likely that most of the aj constants reported in Table 7 are applicable in dipolar aprotic solvents and probably in nonpolar aprotic solvents and in the gas phase as well. Certain substituents do have effects that are strongly dependent on the media. Those groups include charged substituents and protonic substituents capable of hydrogen bond formation. 

The results of the correlations clearly demonstrates the applicability of the <7/j+ constants in protic solvents. Sets 6 and 17 suggest that they are also applicable in dipolar aprotic solvents whereas set 21 indicates that they may be applied to work in gas phase. These latter results are only suggestive however, further work is required to establish beyond any doubt the applicability of the or constants in dipolar aprotic and nonpolar aprotic solvents and in the gas phase. 

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