DMSO, nonaqueous solvents

While water has been used as a solvent more than any other media, nonaqueous solvents [e.g., acetonitrile, propylene carbonate, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or methanol] have also frequently been used. Mixed solvents may also be considered for certain applications. Double-distilled water is adequate for most work in aqueous media. Triple-distilled water is often required when trace (stripping) analysis is concerned. Organic solvents often require drying or purification procedures. These and other solvent-related considerations have been reviewed by Mann (3). 

Results in other solvents are scanty for metals other than Hg. Liquid Ga and its T1 and In liquid alloys have been studied in DMSO, DMF, NMF, AN,343,894 MeOH360 andEtOH.361 Among solid metals, only Bi,28,152 Au,25,26,109 Al,750,751 and Fe729 have been investigated in a number of nonaqueous solvents. Pt and Pd have been studied in DMSO and... 

The general picture emerging from the pzc in aqueous solutions is that the major variation of <7-0 between two metals is due to with a minor contribution from AX that is governed by metal-solvent interactions. If this is also the case in nonaqueous solvents, a similar picture should be obtained. This is confirmed by Fig. 20 in which the data in DMSO are reported. As in aqueous solution, all points lie to the left of the point of Hg. Bi, In(Ga), and Tl(Ga) lie with Hg on a common line deviating from the unit slope. As in aqueous solution, Ga is further apart. Au is in the same position, relatively close to the Hg line. Finally, the point of Pt is (tentatively) much farther than all the other metals. 

Ito et al.40 examined the electrochemical reduction of C02 in dimethylsulfoxide (DMSO) with tetraalkylammonium salts at Pb, In, Zn, and Sn under high C02 pressures. At a Pb electrode, the main product was oxalic acid with additional products such as tartaric, malonic, glycolic, propionic, and n-butyric acids, while at In, Zn, and Sn electrodes, the yields of these products were very low (Table 3), and carbon monoxide was verified to be the main product even at a Pt electrode, CO was mainly produced in nonaqueous solvents such as acetonitrile and DMF.41 Also, the products in propylene carbonate42 were oxalic acid at Pb, CO at Sn and In, and substantial amounts of oxalic acid, glyoxylic acid, and CO at Zn, indicating again that the reduction products of C02 depend on the electrode materials used. 

The NHS ester end of NHS-LC-biotin reacts with amine groups in proteins and other molecules to form stable amide bond derivatives (Figure 11.4). Optimal reaction conditions are at a pH of 7-9, but the higher the pH the greater will be the hydrolysis rate of the ester. Avoid amine-containing buffers which will compete in the acylation reaction. NHS-LC-biotin is insoluble in aqueous reaction conditions and must be solubilized in organic solvent prior to the addition of a small quantity to a buffered reaction. Preparation of concentrated stock solutions may be done in DMF or DMSO. Nonaqueous reactions also may be done with this reagent for the modification of molecules insoluble in water. The molar ratio of NHS-LC-biotin to a... 

The electroreduction of sulfur in nonaqueous solvents (DMF, DM SO etc.) has been studied by several authors for the past 35 years [47-60]. Experimentally, a solution of sulfur is yellow (pale) and the reduced solutions are intensely colored. Electrochemically, the response of the electroreduction of sulfur in classical organic solvent (DMF, DMA, DMSO, CH3CN etc.) is similar. The reduced forms, that is, polysulfides S or S , have characteristic absorption bands in the visible range. Structurally, sulfur is a ring and polysul-fldes are expected to be Knear chains. To understand the electrochemical behavior of sulfur, it was necessary to take into account these structural aspects. This was done only in 1997 [60]. 

The behavior of the Zn(II)/Zn(Hg) system in nonaqueous solvents containing tetraalkylammonium perchlorate ions was presented in works [70-73]. The data show that the standard rate constant, kg, in DMF and DMSO [70] solutions changes with size of the electrolyte cation in the order kg (TPA+) > kg (TBA+) > kg (TEA+) kg... 

Double layer at both pc-Au and singlecrystal Au electrodes brought in contact with such nonaqueous solvents as dimethylsulfoxide (DMSO), dimethylfor-mamide (DMF), acetonitrile, propylene carbonate (PC), and selected alcohols has also been studied. The experimental methods used involved CV and impedance measurements, except for butanol isomers, for which surface-enhanced... 

Photoreduction of cobalt(III) complexes in nonaqueous solvent systems has been little studied because of the limited solubility of cobalt(III) complexes and their tendency to photooxidize the solvent. Irradiation with 365-mjj. light of cis- or trans-Co(en)2C 2 + and Co(en)2Cl(DMSO)2+ in dimethylsulfoxide (DMSO) leads rapidly to production of a green tetrahedral cobalt(II) product apparently with concurrent solvent oxidation.53,71 Irradiation with 365-mjx light of the molecular Co(acac)3 in benzene rapidly gives a red precipitate which may be the cobalt(II) acetylacetonate.53... 

Infant formula Disperse sample in nonaqueous solvent mixture (DMSO/DMF/ CHC13, 2 + 2+1) containing 0.1% (w/v) ascorbic acid. Partition total lipid fraction into hexane, centrifuge. Radial-PAK cartridge containing Resolve silica 5 /xm... 

The reactions are usually carried out [201,202] in nonaqueous solvents (Solv) (alcohols, acetonitrile, DMF, and DMSO) which take part mainly as ligands in formed molecular complexes. Additionally to them, the nitrogen-containing bases (pyridine, bipy, 1,10-phen) were used. Co, Ni, Cu, Zn, Cd, Pb have mainly been applied as a source of complex-former. The ammonium salts are represented by halides and pseudohalides, in particular rhodanides, which have been used especially widely [664-675],... 

In many cases, only the first point is important, and thus a great deal of work in this field has been carried out with protic nonaqueous solvents such as alcohols (MeOH, EtOH, IPrOH) and acids (e.g., acetic acid) [99-105], However, there are many reactions for which the second and third points are also relevant. Hence, there are many reports on the use of solvents such as acetonitrile, methylene chloride, THF, DMSO, DMF, and electrolytes from the R +X- family (R = alkyl, X = CE, BF4E etc.) in unique organic synthesis. Several typical examples are summarized in Table 11 [106-115],... 

Dimethyl sulfoxide is an important solvent in nonaqueous electrochemistry due to its high polarity (dielectric constant of 47), its high donor number (29.8), and a relatively wide electrochemical window. The limiting cathodic voltages in which this solvent can be used depend on the cation used (as expected from the discussion on the cation effects on the reduction processes of the above nonaqueous solvents). Using salts of alkali metals (Li, Na, K), the cathodic limit obtained was around -1.8 — -2 V versus SCE [49], whereas with tetrabutyl ammonium, the cathodic limit was as low as -2.7 — -3 V versus SCE [49], There is evidence that in the presence of Na ions, DMSO reduction produces CH4 and H2 on plati-... 

A primary reason for low yields of 5-HMF is its rapid conversion to levulinic acid in aqueous media. However, catalysis of the transformation with lanthanides has led to dramatic increases in the yield of 5-HMF. The effectiveness of different lanthanide cations has been surveyed.490,491 In nonaqueous solvents, such as DMSO, almost quantitative yields of 5-HMF have been reported.492 Performing the dehydration in the presence of activated carbon (to adsorb the generated 5-HMF) has also been reported as effective.493... 

In nonaqueous solvents such as DMSO-d6, complementary nucleosides will form Watson-Crick base pairs that can be monitored by NMR. The spectra of guanosine and cytidine, both separately and together, are shown in Figure 14.27. For guanosine, the observed resonances include Hg at 5 8.6, NH2 at 5 7.2, and the Hr at 5 6.4. For cytidine, the observed resonances are H6 at 5 8.5, NH2 at 5 7.8, H < at 5 6.5, and H5 at 5 6.45. In a 1 1 mixture, the resonances for the amine protons of both the guanosine and cytidine bases are shifted downfield due to hydrogen bond formation. In addition, the... 

Many salts are soluble in DMSO, so the choice of supporting electrolyte is less restricted than in most other nonaqueous solvents. In general, perchlorates, even KCIO4, nitrates, and halides, are soluble, whereas fluorides, cyanides, sulfates, and carbonates are not thus not only NaC104, LiCl, NaNO, and tetraalkylammonium salts can be used but also such salts as NH4PF6 and NH4SCN. The ability of DMSO to solvate ions is also of importance in the indirect electrolytic hydrodimerization of, for example, acrylonitrile using Na(Hg) [388]. 

According to M Halla and coworkers [206], halogenated benzophenones behave in two different ways in nonaqueous solvents such as DMF, DMSO, and MeCN. For m-fluoro-, p-fluoro-, and m-chlorobenzophenone, a pair of electrons is apparently involved in the reduction, and benzophenone is produced quantitatively. However, for the electrolysis of p-chloro-, m-bromo-, and p-bromobenzophenone, fewer than two electrons per molecule are transferred, and benzophenone is obtained in less than 100% yield. For p-bro-... 

Electrochemical reduction of CO2 in nonaqueous solutions is significant from the following viewpoints Firstly, hydrogen evolution reaction can be suppressed. Secondly, the concentration of water as a reagent can be accurately regulated and the reaction mechanism may be more easily studied. Thirdly, the solubility of CO2 in organic solvents is much liigher than in water. Various metal electrodes have been tested for CO2 reduction in some nonaqueous solvents, such as propylene carbonate (PC), acetonitrile (AN), DMF, and dimethyl sulfoxide (DMSO), as tabulated in Table 5. Methanol is also used for CO2 reduction, and mentioned in the next Section. 

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