Acidity constant formamide

Formamide is difficult to purify. Mandel and Decroly determined the acidity constants of formic and acetic acids in formamide at six... 

Hydrolysis of TEOS in various solvents is such that for a particular system increases directiy with the concentration of H" or H O" in acidic media and with the concentration of OH in basic media. The dominant factor in controlling the hydrolysis rate is pH (21). However, the nature of the acid plays an important role, so that a small addition of HCl induces a 1500-fold increase in whereas acetic acid has Httie effect. Hydrolysis is also temperature-dependent. The reaction rate increases 10-fold when the temperature is varied from 20 to 45°C. Nmr experiments show that varies in different solvents as foUows acetonitrile > methanol > dimethylformamide > dioxane > formamide, where the k in acetonitrile is about 20 times larger than the k in formamide. The nature of the alkoxy groups on the siHcon atom also influences the rate constant. The longer and the bulkier the alkoxide group, the lower the (3). 

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.]...

FORMAMIDE. Form amide (meibanamide), HCONHi. is the lirsi member of the primary amide series and is the only one liquid at room temperature. II is hygroscopic and has a faint odor of ammonia. Formamide is a colorless to pale yellowish liquid, freely miscible with water, lower alcohols and glycols, and lower esters and acetone. It is virtually immiscible in almost all aliphatic and aromatic hydrocarbons, chlorinated hydrocarbons, and ethers. By virtue of its high dielectric constant, close to that of water and unusual for an organic compound, formamide has a high solvent capacity lor many heavy-metal salts and for salts of alkali and alkalinc-carth metals. It is an important solvent, in particular for resins and plasticizers. As a chemical intermediate, formamide is especially useful in the synthesis of heterocyclic compounds, pharmaceuticals, crop protection agents, pesticides, and for the manufacture of hydrocyanic acid. 

PfirrwYYkT r.H.mm.i. mw aa. nu rn. —77.91% white powdr transition pt 160° (loss of w of hydration, Ref 5) and 225° decompn pt 290° (Ref 6). Sol in ethanol, dimethyl formamide, acet, tetrahydrofuran and dimethyl sulfoxide si sol in benz and w. According to Satriana (Ref 6) the dibasic salt is prepd in 92.5% yield by reacting Pb monoxide with /J-resorcylic acid in a 1 3 molar ratio in 50% ethanol at RT for five hours under a current of air. The prod is filtered off, washed with ice cold 50% ethanol and oven dried at 100° to constant wt... 

Kabanov et al. have studied the radical polymerization of acrylic acid in aqueous solutions [61] (see Chap. 4, Sect. 1.4). A crystaline, syndiotactic polymer was formed at pH 10.2-10.8. The kinetics of the photosensitized polymerization of acrylic acid was studied by Galperina et. al. [62], They observed a strong solvent dependence for the rate constant of propagation. At 293 K, kp[mol-1 dm3 s-1] = 22 500 in water, 4 200 in formamide, and 500 in dimethylsulphoxide. 

The carboxylic acid amides most conunonly studied as ligands are formamide, acetamide, and the W-substituted derivatives, particularly A,A-dimethylformamide (DMF). These compounds are often used as solvents and have high dielectric constants, particularly when they contain an N-H bond, and such uses helped to stimulate interest in the amides as ligands. There are two possible donor atoms, N or O, but all complexes of the simple amide ligands, characterized by X-ray structure determination at least, have M-O bonds. The amides are usually terminal ligands but can bridge between metal atoms in some instances. 

There are, however, a number of observations which argue against the viability of such a string of transfers. Firstly, the imidic acid resulting from the tautomerism is considerably higher in energy than the amide. Theoretical and experimental data provide an estimate of an 11-12 kcal/mol energy difference in formamide. The tautomeric equilibrium constant is only some The proton transfer would be impossibly slow it would take more... 

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. 

Deposition of polyelectrolytes Lajimi et al. [56] explored the surface modification of nanofiltration cellulose acetate (CA) membranes by alternating layer-by-layer deposition of acidic chitosan (CHI) and sodium alginate (AEG) as the cationic and anionic polyelectrolyte, respectively. The supporting CA membranes were obtained by a phase separation process from acetone/formamide. The permeation rate of salted solutions was found to be higher than that of pure water. The rejection of monovalent salt was decreased, while that of divalent salt remained constant so that the retention ratio increased. Increasing the concentration of feed solutions enhanced this selectivity effect. 

Formamide is a good solvent for proteins and salts owing to its high dielectric constant. Its main applications are as a solvent in the chemical industry, as a softener for paper, as an intermediate for the manufacturing of formic acid and esters and hydrocyanic acid, and as a reaction medium. 

The apparent acid dissociation constants (p s)Ka) of two water-insoluble drugs, ibuprofen and quinine, were determined pH-metrically in ACN water, dimethyl-formamide water, DMSO water, 1,4-dioxane-water, ethanol water, ethylene glycol-water, methanol water, and tetrahydrofuran water mixtures. A glass electrode calibration procedure based on a four-parameter equation (pH = alpha-i- SpcH -i-jH[H+] -i-jOH[OH ]) was used to obtain pH readings based on the concentration scale (pcH). We have called this four-parameter method the Four-Plus technique. The Yasuda Shedlovsky extrapolation p s)K a + log [H2O] = A/epsllon -1- B) was used to derive acid dissociation constants in aqueous solution (pKa). It has been demonstrated that the pK a values extrapolated from such solvent-water mixtures are consistent with each other and with previously reported measurements. The suggested method has also been applied with success to determine the pKa values of two pyridine derivatives of pharmaceutical Interest. Spectrometric, ultraviolet (UV) ... 

Very few studies have considered the behavior of ionomers in relatively polar solvents, i.e., solvents with high dielectric constants, e. Schade and Gartner(8) compared the solution behavior of ionomers derived from copolymers of styrene with acrylic acid, methacrylic acid, or half esters of maleic anhydride in tetra-hydrofuran (THF), a relatively non-polar solvent (e 7.6), and dimethyl formamide (DMF), a polar solvent (e = 36.7). They ob-... 

---