Dimethyl sulfoxide Dimethylformamide

Alcoholic potassium hydroxide or sodium hydroxide are normally used to convert the halohydrins to oxiranes. Other bases have also been employed to effect ring closure in the presence of labile functional groups such as a-ketols, e.g., potassium acetate in ethanol, potassium acetate in acetone or potassium carbonate in methanol.However, weaker bases can lead to solvolytic side reactions. Ring closure under neutral conditions employing potassiunT fluoride in dimethyl sulfoxide, dimethylformamide or A-methyl-pyrrolidone has been reported in the patent literature. 

Selectivities of potential hydrometallurgical interest that were demonstrated recently400 are the very good extractions of nickel and cobalt from acetonitrile, propylene carbonate, sulfolane or dimethylformamide by a cation exchanger copper, iron(II), iron(III) and zinc, present in the same solution, are either weakly extracted or are not extracted at all. It is also possible for copper to be extracted selectively from Fe3+ ions with an anion exchanger in dimethyl sulfoxide, dimethylformamide or dimethylacetamide.400... 

Substrates that are sparingly soluble in water should be dissolved in a relatively nontoxic, water-miscible solvent, such as ethanol, acetone, 1,2-propanediol, dimethyl sulfoxide, dimethylformamide or 2-methoxyethanol, prior to addition to the culture. Alternatively, solubility can be enhanced by the addition of an emulsifying agent (e.g., Tweens) or by grinding crystalline substrates to micron-size particles. 

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. 

Electrophilic cyclopropanes 392, which are useful intermediates in organic syntheses, can be prepared by the cyclopropanation of olefins with diethyl dibromomalonate and its derivatives (81MI4). The reaction is carried out in the presence of 1 mol equiv. of copper(II) bromide and 2-4 mol equiv. of DBU. Alternatively, the reaction can be effected with diethyl bromomalonate (83BCJ2687) in the presence of a catalytic amount of copper(II) bromide and a slight excess of DBU in benzene at ambient temperature. When some other base (e.g., triethylamine, DABCO, pyridine, or sodium hydride) was applied instead of DBU, the yield was lower or no reaction occurred. The use of other copper salts led to a decrease in the yield. When cyclopropanation was carried out in dimethyl sulfoxide, dimethylformamide, or acetonitrile, the yield of product 392 was again lower. 

Many substituted anilines are investigated139,140 as free bases and hydrogen bonded molecules (generally in CC14 solutions), in order to identify spectral characteristics of absorption bands of free and 1 1 or 1 2 complexes with several proton acceptor partners mainly tetrahydrofuran, dimethyl sulfoxide, dimethylformamide and dioxane are used. 

Dlethylamlne Dimethyl Phthalate Dimethyl Sulfoxide Dimethylformamide DIoctyl Phthalate... 

The fast and sufficiently complete reaction proceeds in dimethyl sulfoxide, dimethylformamide, hexamethylphosphotriamide, and excess 4-vinylpyridine, but the best results were achieved in N-methyl-N-butylimi-dazolium tetrafluoroborate, an ionic liquid. The final polymers demonstrate a noticeable volume increase by taking up as much organic solvents, both polar and nonpolar, and even water, as a hypercrosslinked polystyrene crosslinked with the same crosslinking agent (Table 9.4). Still, the specific surface area of the hydrophilic hypercrosslinked polymer is smaller than that of the hypercrosslinked polystyrene, being less than 100 m/g. In all probability, the rigidity of the hypercrosslinked vinylpyridine product is... 

The effect of solvent on the site of alkylation has been clearly demonstrated for phenolate ions. In solvents such as dimethyl sulfoxide, dimethylformamide, ethers, and alcohols, O-alkylation is dominant. In water, phenol, and trifluoroethanol, however, extensive amounts of C-alkylation occur. These latter solvents would be expected to form particularly strong hydrogen bonds with the oxygen atom of the phenolate anion. This strong solvation decreases the reactivity at oxygen and favors carbon alkylation. 

There are PAI types that are used as coatings [88]. The types with thermosetting properties are used. The polymer is delivered in the unimidized or amic acid form. Upon heating, the polymer will undergo cycliza-tion to the imide form. The cycUzation reaction is shown in Figure 14.9. The imidization reaction occurs in the temperature range of 90-150 °C. Solvents for the amic acid form include DMAC, dimethyl sulfoxide, dimethylformamide, and NMP. NMP is preferred, because it has a low odor and a relatively low level of toxicity. 

The reactivity of the pendant chloromethyl side group of polyepichlorohydrin and copolymers containing epichlorohydrin units has been used to make a variety of interesting functional polymers. In aprotic solvents such as dimethyl sulfoxide, dimethylformamide, etc., these side groups undergo substitution reactions with nucleophilic reactants such as amines (25) and... 

Water is the best solvent (often the only good one) for the Werner complex salts. Some use has been made recently of nonaqueous solvents such as methanol, dimethyl sulfoxide, dimethylformamide, and acetonitrile. However the bulk of the work on the syntheses, reactions, equilibria, and kinetics of these systems has been done with water solutions. It is not surprising then to find that the most extensively studied reaction is that of aquation. The rate of such a reaction, Eq. (21), can often be followed conveniently by means of more than one experimental technique. 

---