Anion dimethylsulfoxide

This reaction sequence illustrates how the rates of many base-catalyzed reactions can be enhanced greatly by substitution of dimethylsulfoxide for the usual hydroxylic solvents. Other examples of the enhanced reactivity of anions in dimethylsulfoxide are found in Wolff-Kishner reductions and Cope elimination reactions. The present reaction illustrates the generation of an aryne intermediate from bromobenzene. ... 

Let us compare anion-radicals with dianions, which are definitely stronger bases. For example, the cyclooctatetraene dianion (CgHg ) accepts protons even from solvents such as dimethylsulfoxide (DMSO) and V,V-dimethylformamide. The latter is traditionally qualified as an aprotic solvent. In this solvent, the cyclooctatetraene dianion undergoes protonation resulting in the formation of cyclooctatrienes (Allendoerfer and Rieger 1965) + 2H+ CgHjo. It is seen that... 

As for solvents, liquid ammonia or dimethylsulfoxide are most often used. There are some cases when tert-butanol is used as a solvent. In principle, ion-radical reactions need aprotic solvents of expressed polarity. This facilitates the formation of such polar forms as ion-radicals are. Meanwhile, the polarity of the solvent assists ion-pair dissociation. This enhances reactivity of organic ions and sometimes enhances it to an unnecessary degree. Certainly, a decrease in the permissible limit of the solvent s polarity widens the possibilities for ion-radical synthesis. Interphase catalysis is a useful method to circumvent the solvent restriction. Thus, 18-crown-6-ether assists anion-radical formation in the reaction between benzoquinone and potassium triethylgermyl in benzene (Bravo-Zhivotovskii et al. 1980). In the presence of tri(dodecyl)methylammonium chloride, fluorenylpi-nacoline forms the anion-radical on the action of calcium hydroxide octahydrate in benzene. The cation of the onium salts stabilizes the anion-radical (Cazianis and Screttas 1983). Surprisingly, the fluorenylpinacoline anion-radicals are stable even in the presence of water. 

Dimethylformamide Dimethylglyoxime mono-anion 2,9-Dimethyl-1,10-phenanthroline Dimethylsulfoxide (upper case for solvent, lower-for ligand)... 

The second critical test of this conjugate base mechanism is based on the fact that this five-coordinated intermediate, if indeed it exists, would not always have to react with the solvent, though the solvent would be what it would react with under most circumstances. We have run this type of base hydrolysis in the presence of many anions of high concentration, and the only thing that we can find is the hydroxo complex so at least in water solution, water seems to be what this five-coordinated intermediate picks up. But in dimethylsulfoxide it certainly is possible to throw in various anions, and since dimethylsulfoxide is not as good as water in coordination, other nucleophiles may react. We do find in dimethylsulfoxide that a base, such as hydroxide ion, speeds up the rate of base hydrolysis but the product, instead of being a hydroxo compound, is the complex corresponding to whatever anion we have added, such as nitrite ion, azide ion, and thiocyanate ion. 

Preparation The dimsyl anion is generated from dimethylsulfoxide (DMSO) by use of base. The resulting lithio- or sodio- derivative is generally used in the DMSO solvent. 

In other enzymes such pockets are thought to be the sites for nucleotide binding142. A completely different type of agents which reversibly affect the calcium transport and calcium-dependent ATP splitting are substances like dimethylsulfoxid and ethyleneglycol143. They do not interfere with ATP binding as chaotropic anions do. 

The Validity of the J Function. For aqueous sodium hydroxide solutions the validity of the J- function, describing the basicity of a solution by its ability to add hydroxide ions to a carbonyl group to form an anion of the geminal diol, has been proved earlier (19). For all substituted benzaldehydes studied in water-ethanol or water-dimethylsulfoxide (DMSO), the value of log (CArCH(OH)o-/CArCHo) determined from absorbance measurements was found to be a linear function of the J- function with a slope varying between 0.95 and 1.05 in the region of J values where measurements were possible. The Can-... 

Isatin, JV-methylisatin, and JV-hydroxyisatin can be reduced to semidiones by treatment with the enolate anion of propiophenone in dimethylsulfoxide.258 Nitroxides are prepared from iV-hydroxyisatin by treatment with lead dioxide in dioxan, while another nitroxide was formed spontaneously from iV-hydroxyisatin in basic dimethyl sulfoxide solution in the presence of oxygen.256... 

If an electron acceptor is available in homogeneous solution, photochemical reaction can be observed. For example, when 2 is excited (X > 350 nm) in anhydrous dimethylsulfoxide (DMSO), methylation occurs, ultimately giving rise to 9,9-dimethyl-fluorene in >80% yield. By analogy with Tolbert s mechanism for photomethylation in DMSO (4), such a process may be initiated by electron transfer to DMSO to form a caged radical-radical anion pair from which subsequent C-S cleavage occurs (eqn 4). 

Compound 14 could be made this way or alternately from the anion of dimethylsulfoxide (13) followed by oxidation to the sulfone with KMn04. This compound, although nicely crystalline, was difficult to purify and we found it better to make the morpholino derivative, Compound 18, which handled much better. 

Eggins and McNeill compared the solvents of water, dimethylsulfoxide (DMSO), acetonitrile, propylene carbonate, and DMF electrolytes for C02 reduction at glassy carbon, Hg, Pt, Au, and Pb electrodes [78], The main products were CO and oxalate in the organic solvents, while metal electrodes (such as Pt) which absorb C02 showed a higher production for CO. In DMF, containing 0.1 M tetrabutyl ammonium perchlorate and 0.02 M C02 at a Hg electrode, Isse et al. produced oxalate and CO with faradaic efficiencies of 84% and 1.7%, respectively [79], Similarly, Ito et al. examined a survey of metals for C02 reduction in nonaqueous solution, and found that Hg, Tl, and Pb yielded primarily oxalate, while Cu, Zn, In, Sn, and Au gave CO [80, 81]. Kaiser and Heitz examined Hg and steel (Cr/Ni/Mo, 18 10 2%) electrodes to produce oxalate with 61% faradaic efficiency at 6 mA cm-2 [82]. For this, they examined the reduction of C02 at electrodes where C02 and reduction products do not readily adsorb. The production of oxalate was therefore explained by a high concentration of C02 radical anions, COi, close to the surface. Dimerization resulted in oxalate production rather than CO formation. 

There are several cases of hydroxylation according to the hidden radical mechanism, within a solvent cage. As assumed (Fomin Skuratova 1978), hydroxylation of the anthraquinone sulfonic acids (AQ-SO3H) proceeds by such a pathway, and OH radicals attack the substrate anion radicals in the solvent cage. Anthraquinone hydroxyl derivatives are the final products of the reaction. In the specific case of dimethylsulfoxide as a solvent, hydroxyl radicals give complexes with the solvent and lose their ability to react with the antraquinone sulfonic acid anion radicals (Bil kis Shein 1975). The reaction is stopped just after anion radical formation, Scheme 1-102 ... 

Solodovnikov (1976) studied the kinetics of the interaction of the 4-nitro-l-chlorobenzene with sodium methylate in dimethylsulfoxide in air via the method of spectrophotometry. Kinetic calculations were made in an assumption that all the anion radicals of 4-nitro-l-chlorobenzene are converted into 4-nitrophenolate. The calculations gave a sum of rate constants for formation of 4-nitroanisole and of the 4-nitro-l-chlorobenzene anion radicals close to the rate constant for the consumption of 4-nitro-l-chlorobenzene. Solodovnokov (1976) concluded that the anion radicals of 4-nitro-l-chlorobenzene are produced by a reaction parallel to substitution. Then it should be assumed that the reaction proceeds either by a nonradical mechanism or by a hidden radical mechanism, which implies that particles of a radical nature are produced and unite in a solvent cage without passing into a solvent pool. This conclusion generated objections (Shein 1983). The discussion deserves our consideration because it reveals features and limitations of the method for discerning the ion radical nature of a reaction. 

Shein (1983) paid attention to the following facts. Dimethylsulfoxide used as a solvent may contain water and MeSNa. Water may hydrolyze the initial 4-nitro-l-chlorobenzene (spectrophotometry uses solutions extremely diluted with respect to the substrate). The presence of MeSNa may cause the formation of 4-nitrophenylmethyl sulfide and its anion radical, and this was not included in the kinetic equations. Solodovnikov (1976) considers neither the production of 4-nitroanisole nor the formation of the other products of a deeper reduction of the substrate. 

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