Dimethylformamide, solvent system

As, for the most part, the corresponding ester derivatives are a more important synthetic target, recent literature has demonstrated methods to prepare the esters directly. Examples include the use of nickel carbonyl in a methanol/dimethylformamide solvent system(37) the direct conversion of benzyl alcohol to methylphenyl-acetate using cobalt carbonyl(38) and a reaction system which utilizes an ammonium salt bound to an organic polymer(39). 

The cyclisation of (22) to the /J-lactam system, which is a thermodynamically unfavourable reaction, is promoted by using sodium hydride as the base in a dichloromethane-dimethylformamide solvent system at high dilution. 

CeUulose triacetate is insoluble in acetone, and other solvent systems are used for dry extmsion, such as chlorinated hydrocarbons (eg, methylene chloride), methyl acetate, acetic acid, dimethylformamide, and dimethyl sulfoxide. Methylene chloride containing 5—15% methanol or ethanol is most often employed. Concerns with the oral toxicity of methylene chloride have led to the recent termination of the only triacetate fiber preparation faciHty in the United States, although manufacture stiH exists elsewhere in the world (49). 

Liquid—hquid extraction can be used to obtain high purity linoleic acid from safflower fatty acids or linoleic acid from linseed fatty acids using furfural and hexane as solvents (18). High purity linoleic acid has been obtained from sunflower fatty acids using a dimethylformamide and hexane solvent system (19). 

Subsequently, several laboratories developed improvements in the early procedures. It was first recommended that the reaction be carried out at a low temperature ca. —T) for better results. A more notable improvement is the use of dimethylformamide-t-butanol as the solvent system, a temperature range of —20 to —25°, and the presence of triethyl phosphite during the reaction to reduce the hydroperoxide as it is formed. The triethyl phosphate which is produced is water soluble and overall yields are generally in the range of 60-70 %. 

Likewise, perfluoronaphthalene has been reacted with sodium hydrogen sulfide.42 The reaction was carried out with a 2 1 ratio of hydrogen sulfide to perfluoronaphthalene in the more polar dimethylformamide/ethylene glycol (5 1) solvent system at — 6 °C over 45 min, yielding... 

The first general comment relates to the solvent system. In those cases where the electrolysis substrate does not exist in an aqueous-ethanolic or methanolic solution in a suitable ionic form, it is necessary to provide a solvent system of low electrical resistance which will dissolve the substrate, and also a supporting electrolyte whose function is to carry the current between the electrodes. Examples of such solvents are dioxane, glyme, acetonitrile, dimethylformamide and dimethyl sulphoxide supporting electrolytes include the alkali metal halides and perchlorates, and the alkylammonium salts (e.g. perchlorates, tetrafluoro-borates, toluene-p-sulphonates). With these electrolysis substrates, mass transfer to the electrode surface is effected by efficient stirring. 

In view of the already extensive and rapidly expanding literature concerning NMA, the present comprehensive review will be restricted to the use of pure NMA as a solvent. The literature has been covered rigorously through 1975 and in major part through 1976. Much of the NMA-related literature, especially that in the 1970 s, deals with the properties and chemistry of mixed-solvent systems in which NMA is combined with water, N,N-dimethylformamide, N,N-dimethylacetamide, t-butyl alcohol, dimethyl sulfoxide, or other solvents hence, it is currently anticipated that the broad topic of NMA-containing mixed-solvent systems will be covered in another review. 

Different. solubility behaviors were observed in organic solvent systems. Regenerated cellulose did not dissolve in the SOj-amine-DMSO system which, however, readily dissolved the native and mercerized samples [15-17]. Similarly, rayon and mercerized cellulose, unlike native cellulose, were insoluble in the dimethylformamide (DMS)-chloral-pyridine solvent system 114]. Thus, the morphology of the amorphous component in addition to its content plays a significant role in the overall reactivity of cellulose. 

Although solvents such as dimethylformamide have been tried, the use of anhydrous benzene and anhydrous hydrogen cyanide appears to remain as the most general nonaqueous solvent system and several new Reissert compounds have been prepared by this method. " With the use of anhydrous hydrogen cyanide this method suffers from an obvious disadvantage. 

However, only limited experimental studies on the thermodynamic properties of polypeptide solutions have been carried out. The results of vapor sorption studies for PBLG and poly(P-benzyl L-aspartate) solutions at high polymer concentrations by Flory and Leonard could not be explained by the Flory model, but could be explained by assuming that mixing of solvent with flexible side chains dominates the thermodynamic behavior at high concentrations. Rai and Miller obtained similar results for the PBLG-dimethylformamide (DMF) system at high concentrations. They also showed that the results could be explained by the Wee-MiUer theory in which modification of Flory s lattice theory to allow for side chain... 

Aminabhavi, T.M., Gopalakrishna, B., 1995. Density, viscosity, refractive index, and speed of sound in aqueous mixtures of A,A-dimethylformamide, dimethylsulfoxide, A,A-dimethylace-tamide, acetonitrile, ethylene glycol, diethylene glycol, 1,4-dioxane, tetrahydrofuran, 2-methoxyethanol, and 2-ethoxy-ethanol at 298.15 K. J. Chem. Eng. Data 40, 856-861. Barzegar-Jalali, M., Jouyban-Gharamaleki, A., 1996. Models for calculating solubility in binary solvent systems. Int. J. Pharm. 140, 237-246. 

The Rm values obtained in different solvent systems are similar for acetone or methanol aqueous mobile phases, but for AW-dimethylformamide, they are significantly lower. This observation can be explained by the structure of AW-dimethylformamide, which is very different from water. 

For these reactions, a large variety of base-solvent systems have been used, including sodium hydride in 1,2-dimethoxyethane or dimethylformamide, aqueous sodium hydroxide, butyl-lithium or phenyllithium in hexanes, potassium hydride in tetrahydrofuran, and sodium ethox-ide in ethanol. 

Except for extracts with anhydrous EDA, data in Table 4 were obtained for humic substances isolated from an air-dried H+-exchanged humic histosol soil. For extractions with pyridine, A,A-dimethylformamide (DMF), di-methylsulfoxide (DMSO), and sulfolane, soils (60 g) were thoroughly mixed with the appropriate solvent (250 cm ). After centrifugation the residues were repeatedly extracted with water until the supernatants were only faintly colored. Supernatants for each of the solvent systems were combined and the pH values of the solutions were adjusted to 1.0 using 5M hydrochloric acid. Humic and fulvic acids were separated by centrifugation. 

A chief advantage of the procedure outlined is that the method can be used for multiple drug substances, provided that the OVIs used are included in the 23-component set. Moreover, for use with different drug substances, the only validation criterion is to verify that the drug substance does not alter the distribution coefficients between the solvent and headspace. For samples that are insoluble in DMI, other solvents such as N,N-dimethylacetamide or N,N-dimethylformamide (DMF) may be used. Alternatively, DMI may be modified with water. The use of water can promote the distribution of OVIs into the headspace, but can have deleterious effects on the GC column. As a change in the sample solvent will influence the distribution of the solvent and the headspace, more extensive validation is required when the solvent system is changed. 

Few studies have been conducted heretofore on sulfonated ionomers in solvents which can be considered relatively polar, as defined by a high dielectric constant. A recent study (13) on acrylonitrile-methallyl sulfonate copolymers in dimethyl-formamide is a notable exception. S-PS is readily soluble in a wide variety of solvents, some of them exhibiting rather high values of dielectric constant, such as dimethylformamide (DMF) or dimethylsulfoxide (DMSO). The reduced viscosity-concentration behavior of sulfonated polystyrene is markedly different in polar solvents from that in nonpolar-solvent systems. Typically there is a marked upsweep in reduced viscosity at low polymer concentrations and clearly a manifestation of classic polyelectrolyte behavior. ( 7)... 

Polar solvents such as dimethylformamide, dimethylsulfoxide, and tetrahydrofuran-water mixtures behave differently in that polyelectrolyte behavior is observed at extreme dilution for sulfonate ionomers therefore, the behavior described above does not apply directly to these solvent systems. 

According to Eq. (16), the difference between the differential heats of solution of two polymorphs is a measure of the heat of transition AH between the two forms. Because enthalpy is a state function (Hess s law), this difference must necessarily be independent of the solvent system used. However, conducting calorimetric measurements of the heats of solution of the polymorphs in more than one solvent provides an empirical verification of the assumptions made. For instance, AH values of two losartan polymorphs were found to be 1.72 kcal/mol in water and 1.76 kcal/mol in dimethylformamide [53]. In a similar study with moricizine hydrochloride polymorphs, AH values of 1.0 kcal/mol and 0.9 kcal/mol were obtained from their dissolution in water and dimethylformamide, respectively [54]. These two systems, which show good agreement, can be contrasted with that of enalapril maleate, where was determined to be 0.51 kcal/mol in methanol and 0.69 kcal/mol in acetone [55]. Disagreements of this order (about 30%) suggest that some process, in addition to dissolution, is taking place in one or both solvents. 

---