Dimethyl sulfoxide dielectric constant

Solvent for Displacement Reactions. As the most polar of the common aprotic solvents, DMSO is a favored solvent for displacement reactions because of its high dielectric constant and because anions are less solvated in it (87). Rates for these reactions are sometimes a thousand times faster in DMSO than in alcohols. Suitable nucleophiles include acetyUde ion, alkoxide ion, hydroxide ion, azide ion, carbanions, carboxylate ions, cyanide ion, hahde ions, mercaptide ions, phenoxide ions, nitrite ions, and thiocyanate ions (31). Rates of displacement by amides or amines are also greater in DMSO than in alcohol or aqueous solutions. Dimethyl sulfoxide is used as the reaction solvent in the manufacture of high performance, polyaryl ether polymers by reaction of bis(4,4 -chlorophenyl) sulfone with the disodium salts of dihydroxyphenols, eg, bisphenol A or 4,4 -sulfonylbisphenol (88). These and related reactions are made more economical by efficient recycling of DMSO (89). Nucleophilic displacement of activated aromatic nitro groups with aryloxy anion in DMSO is a versatile and useful reaction for the synthesis of aromatic ethers and polyethers (90). 

The effect of solvents on the kinetics of addition to hexyne-1 was studied (56) with Et3SiH. Solvents with dielectric constants from 1.6 to 20.7 had scarcely any measureable effects on the rates of addition. Electron-donating solvents such as pyridine or dimethyl sulfoxide even in very small amounts stopped the reaction entirely. 

FIGURE 3 2 Solvent extraction efficiencies (EF) as functions of dielectric constants (D), solubility parameters (6), and polarity parameters (P and E -). Solvents studied silicon tetrachloride, carbon disulfide, n pentane. Freon 113, cyclopentane, n-hexane, carbon tetradiloride, diethylether, cyclohexane, isooctane, benzene (reference, EF 100), toluene, trichloroethylene, diethylamine, chloroform, triethylamine, methylene, chloride, tetra-hydrofuran, l,4 dioxane, pyridine, 2 propanol, acetone, ethanol, methanol, dimethyl sulfoxide, and water. Reprinted with permission from Grosjean. ... 

Figure 18. Correlations between the solubility of cmchonidme and the reported empirical polarity (A) and dielectric constants (B) of 48 solvents [66]. Those solvents are indicated by the numbers in the figures 1 cyclohexane 2 n-pentane 3 n-hexane 4 triethylamine 5 carbon tetrachloride 6 carbon disulfide 7 toluene 8 benzene 9 ethyl ether 10 trichloroethylene 11 1,4-dioxane 12 chlorobenzene 13 tetrahydrofuran 14 ethyl acetate 15 chloroform 16 cyclohexanone 17 dichloromethane 18 ethyl formate 19 nitrobenzene 20 acetone 21 N,N-drmethyl formamide 22 dimethyl sulfoxide 23 acetonitrile 24 propylene carbonate 25 dioxane (90 wt%)-water 26 2-butanol 27 2-propanol 28 acetone (90 wt%)-water 29 1-butanol 30 dioxane (70 wt%)-water 31 ethyl lactate 32 acetic acid 33 ethanol 34 acetone (70 wt%)-water 35 dioxane (50 wt%)-water 36 N-methylformamide 37 acetone (50 wt%)-water 38 ethanol (50 wt%)-water 39 methanol 40 ethanol (40 wt%-water) 41 formamide 42 dioxane (30 wt%)-water 43 ethanol (30 wt%)-water 44 acetone (30 wt%)-water 45 methanol (50 wt%)-water 46 ethanol (20 wt%)-water 47 ethanol (10 wt%)-water 48 water. [Reproduced by permission of the American Chemical Society from Ma, Z. Zaera, F. J. Phys. Chem. B 2005, 109, 406-414.]...

Anastopoulos et al. [47] have analyzed interfacial rearrangements of triphenyl-bismuth and triphenylantimony at mercury electrode in nonaqueous solvents of high dielectric constant. These phenomena were detected as the peaks in the capacitance-potential curves at intermediate negative potentials for triphenyl-bismuth and triphenylantimony in N-methylformamide, A,A-dimethylforma-mide, dimethyl sulfoxide, propylene carbonate, and methanol solutions. 

The ideal solvent for electrochemical studies should satisfy a number of requirements. In addition to the properties required for any good solvent for organic chemistry, such as a high solvating power and a low reactivity towards common intermediates, solvents for electrochemical use should be difficult to oxidise or reduce in the potential range of interest. Traditionally, the recommended potential limits are +3 V (versus the SCE) for oxidations and —3 V for reductions. Also, the solvent should have a dielectric constant higher than about 10 in order to ensure that the supporting electrolyte is well dissociated. Commonly used solvents are acetonitrile (MeCN) and dichloromethane for oxidations, and MeCN, N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) for reductions. 

The effective correlation times for an approximately isotropic motion, tr, ranged from 40.3 ps in methanol to 100.7 ps in acetic acid for 5a, and from 61.6 ps to 180.1 ps for 5b in the same solvents. Neither solvent viscosity nor dielectric constant bore any direct relationship to the correlation times found from the overall motion, and attempts to correlate relaxation data with parameters (other than dielectric constant) that reflect solvent polarity, such as Kosover Z-values, Win-stein y-values, and the like, were unsuccessful.90 Based on the maximum allowed error of 13% in the tr values derived from the propagation of the experimental error in the measured T, values, the rate of the overall motion for either 5a or 5b in these solvents followed the order methanol N,N-dimethylformamide d2o < pyridine < dimethyl sulfoxide. This sequence appears to reflect both the solvent viscosity and the molecular weight of the solvated species. On this basis, and assuming that each hydroxyl group is hydrogen-bonded to two molecules of the solvent,137 the molecular weights of the solvated species are as follows in methanol 256, N,N-dimethylformamide 364, water 144, pyridine 496, and dimethyl sulfoxide 312. 

The influence of solvents was extensively studied [38, 40b, 42], with reactions shown capable of being performed in neat, or, virtually in any polar medium. Whilst high dielectric constant oxygenated solvents such as tetrahydrofuran (THF), 1,4-dioxane, acetone (Et20), dimethyl sulfoxide (DMSO), and dimethyl-formamide (DMF) are used in non-asymmetric MBH reactions, dichloroethane (CH2C12) or acetonitrile are preferred for asymmetric transformations. MBH re-... 

Acetonitrile. Acetonitrile is resistant to both oxidation and reduction, is transparent in the region 200-2000 nm, and is an excellent solvent for many polar organic compounds and some inorganic salts. Its dielectric constant of 37 permits reasonably high conductivities, although there is evidence of some association (see Table 7.8). It is less basic than dimethylformamide and dimethyl sulfoxide, and therefore does not solvate alkali metal cations as strongly. However, acetonitrile forms stable complexes with Ag(I) and Cu(I) ions. 

Dimethyl sulfoxide (Me2SO). The applications of Me2SO in electrochemistry have been thoroughly reviewed.93 It is a particularly useful solvent because it has a high dielectric constant and is sufficiently resistant to both oxidation and reduction to provide a fairly wide potential range. It is, however, not as resistant as acetonitrile or propylene carbonate to oxidation and these latter two solvents are preferred over Me2SO for this purpose. 

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-... 

Dimethyl sulfoxide (DMSO) — Organic solvent ((CH3)2SO or DMSO, melting point 18 °C, boiling point 189°C) with a density (1.10gem-3 at 25°C) higher than water. DMSO is highly polar (dielectric constant er = 46.45) and hygroscopic. DMSO is miscible with water in any ratio and can be dried over 4 A molecular sieves [i]. 

Figure 5. Ionization constants of acids in various solvents vs. the dielectric constant function at 25°C. A,B,C ethanol-water (O), methanol-water (A), dioxane-water ( ). B,C acetone-water ( ), glycerol-water (W). B 2-methoxyethanol-water (V), dimethyl-sulfoxide-water (M).

EPD solvents do not correctly reflect the ionizing properties of these solvents due to the differences in dielectric constants. Although Sn(CH3)3l is considerably ionized in pure tributylphosphate, the solutions are essentially nonconducting because of the very low dielectric constant e = 6.8 of this medium (see Section IV). Puoss-Krauss analysis of conductance data for Sn(CH3)3l in strong EPD solvents, such as dimethylformamide (DME), dimethyl sulfoxide (DMSO), pyridine, and hexamethylphosphoric amide (HMPA), reveal that the substrate is completely ionized and consequently behaves as a 1 1 electrolyte (33). 

Useful solvents must themselves resist oxidation or reduction, should dissolve suitable ionic solutes and nonelectrolytes, and in addition should be inexpensive and obtainable in high purity. Kratochvil indicated that the most potentially useful solvents are those that have a dielectric constant greater than about 25 and have Lewis-base properties. Some solvents meeting these criteria are acetonitrile, dimethyl-sulfoxide, dimethylformamide, dimethylacetamide, propylene carbonate, ethylene carbonate, formamide, sulfolane, and y-butyrolactone. Solvents of the Lewis-base type show specific solvation effects with many metal cations (Lewis acids). Thus acetonitrile functions as a Lewis base toward the silver ion. At the same time it reacts but little with the hydrogen ion. 

In either dimethyl-formamide or dimethyl sulfoxide, the reaction rates became too fast to measure even in the absence of a catalyst. It thus appears that while the ionizing power of the solvent as indicated by the dielectric constant is an important factor for the solvent effect, it is not the only one. The slow reaction in the case of acetonitrile may have been caused by the nitrile competing with the isocyanate for the electrons of the base catalyst and thereby neutralizing the catalyst by complexing. 

At 50 volumes percent most of the organic solvents selected decrease the dielectric constant of water from 10 to 30 units depending on the solvent, except for dimethyl sulfoxide, which has a dielectric constant close to that of water (76.0 and 80, respectively at 20°C). 

Fig. 4. Dielectric constant (D) of hydroorganic solvents as a function of percentage in volume. DMSO, dimethyl sulfoxide EGOH, ethylene glycol MeOH, methanol PrOH, propylene glycol MPD, 2-methyl-2,4-pentanediol. Temperature, 20°C. From Douzou (1977b). Reprinted with permission of Academic Press.

Dielectric Constant of Dimethyl Sulfoxide -Water Mixtures 1... 

Dimethylformamide-water mixtures, dielectric constant of, 95 Dimethyl sulfoxide-water mixtures, dielectric constant of, 94... 

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