Formamide dielectric constant

Energy minimization, ccmformational searching and molecular mechanics were performed using Alchemy 2000 program system from Tripos loaded on a PC Pentium Computer. For molecular mechanics optimization, the MM3 Molecular Mechanics siAroutine with a value of 4.7 for dimethyl formamide dielectric constant, a RMS gradient of 0.05 kCai/A mot and a delta of energy of 0.001 kCai/A was used. 

Tables 1 and 2 Hst the important physical properties of formamide. Form amide is more highly hydrogen bonded than water at temperatures below 80°C but the degree of molecular association decreases rapidly with increa sing temperature. Because of its high dielectric constant, formamide is an excellent ionizing solvent for many inorganic salts and also for peptides, proteias (eg, keratin), polysaccharides (eg, cellulose [9004-34-6] starch [9005-25-8]) and resias.

The importance of the solvent, in many cases an excess of the quatemizing reagent, in the formation of heterocyclic salts was recognized early. The function of dielectric constants and other more detailed influences on quatemization are dealt with in Section VI, but a consideration of the subject from a preparative standpoint is presented here. Methanol and ethanol are used frequently as solvents, and acetone,chloroform, acetonitrile, nitrobenzene, and dimethyl-formamide have been used successfully. The last two solvents were among those considered by Coleman and Fuoss in their search for a suitable solvent for kinetic experiments both solvents gave rise to side reactions when used for the reaction of pyridine with i-butyl bromide. Their observation with nitrobenzene is unexpected, and no other workers have reported difficulties. However, tetramethylene sulfone, 2,4-dimethylsulfolane, ethylene and propylene carbonates, and salicylaldehyde were satisfactory, giving relatively rapid reactions and clean products. Ethylene dichloride, used quite frequently for Friedel-Crafts reactions, would be expected to be a useful solvent but has only recently been used for quatemization reactions. ... 

An interesting observation reported in Table XLIX is the increase in the hydroquinone/catechol ratio from 1.44 to 1.99 when the dielectric constant of the medium is decreased from 58.9 to 39.2 by addition of methanol to water. A similar increase in the hydroquinone/catechol ratios was also observed in phenol hydroxylation catalyzed by TS-1 (266) in dioxane-water and tert-butyl alcohol-water mixtures. The para/ortho ratio increased nearly 10-fold when 10% dioxane was added to water. Similarly, the para/ortho ratio more than doubled (1.3-3.0) when 10% tert-butyl alcohol was added to water. An opposite trend, namely, a decrease in the para/ortho ratio from 1.4 to 0.6, was observed when 10% formamide (s = 108) was added to water. Because of geometric constraints in the MFI pores, catechol is expected to be formed more easily on the external surface of TS-1 crystallites than in the pores (91). Hydroquinone, less spatially demanding, can form in the TS-1 channels. A greater coverage of the hydrophobic... 

The recent introduction of non-aqueous media extends the applicability of CE. Different selectivity, enhanced efficiency, reduced analysis time, lower Joule heating, and better solubility or stability of some compounds in organic solvent than in water are the main reasons for the success of non-aqueous capillary electrophoresis (NACE). Several solvent properties must be considered in selecting the appropriate separation medium (see Chapter 2) dielectric constant, viscosity, dissociation constant, polarity, autoprotolysis constant, electrical conductivity, volatility, and solvation ability. Commonly used solvents in NACE separations include acetonitrile (ACN) short-chain alcohols such as methanol (MeOH), ethanol (EtOH), isopropanol (i-PrOH) amides [formamide (FA), N-methylformamide (NMF), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA)] and dimethylsulfoxide (DMSO). Since NACE—UV may present a lack of sensitivity due to the strong UV absorbance of some solvents at low wavelengths (e.g., formamides), the on-line coupling of NACE... 

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.]...

D. L. Chapman, for potassium tri-iodide. 0. Gropp measured the effect of temp, on the conductivity of solid and frozen soln. of sodium iodide. For the effect of press, on the electrical properties, vide alkali chlorides. A. Reis found the free energy for the separation of the ions of K1 to be 144 lrilogrm. cals, per mol. for iN al, 158 Lil, 153 and for HI, 305. S. W. Serkofi 35 measured the conductivity of lithium iodide in methyl alcohol P. Walden, of sodium iodide in acetonitrile P. Dutoit in acetone, benzonitrite, pyridine, acetophenone. J. C. Philip and H. R. Courtman, B. B. Turner, J. Fischler, and P. Walden of potassium iodide in methyl or ethyl alcohol J. C. Philip and H. P. Courtman in nitromethane P. Dutoit in acetone. H. C. Jones, of rubidium iodide in formamide. S. von Lasczynsky and S. von Gorsky, of potassium and sodium iodides in pyridine. A. Heydweiller found the dielectric constants of powdered and compact potassium iodide to be respectively 3 00 and 5 58. 

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. 

Some of the stimulus for studying these systems arose from the availability and use of some of these ligands as solvents, a subject reviewed by Vaughan38 who includes details of methods of purification and electrochemical parameters. The dielectric constants are much higher when these molecules contain an N—H bond thah when they are JV.V -dimethyl substituted. Formamide, its V-methylated derivaties and dimethylacetamide (DMA) are liquids at room temperature iV-methyl-... 

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-... 

Turning now to an assessment of the H-bond energies within a dielectric medium, via explicit inclusion of both the dipeptide and the formamide, relevant data are reported in Table 15-5 for the more stable C7 conformer. A dielectric constant of... 

Fig. 40. Plot of the unperturbed chain dimension A against the total degree of substitution for cellulose acetate (CA)-solvent systems. Solid line CA-DMAc chain line asymptotic A at the limit of the dielectric constant s = I broken line A of cellulose at the free rotational state7 asymptotic A value at the limit of s = 1 asymptotic A value at the limit of e = 1 and = 0 (j formamide ) water (j DMAc O- acetone -O THF O TCE...

Electromotive force measurements of HC1 solutions in pure NMA and in NMA/dioxane solvent mixtures using the silver-silver chloride electrode have been reported by Dawson and his co-workers (1,2,3). The only other potentiometric studies in a solvent of dielectric constant higher than that of water appear to have been in formamide (6,7,8,9, 10) and in N-methylpropionamide (NMP) (11,12,13,14,15). 

The activity coefficients in the mixed solvents are all higher than those in pure water. This suggests that HBr is dissociated completely and does not form ion pairs in mixtures of water and NMA of these compositions. From electrostatic considerations, this is in accord with expectation since mixed solvents have higher dielectric constants than water. This observation is consistent with earlier studies, which showed that the activity coefficient of HC1 is higher in the pure solvents formamide (6,7), NMA (1,2), and NMP (15) than in water. Similarly, our own preliminary results show the same to be true of HBr in pure NMA at 35°C. 

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. 

It is amphoteric, being deprotonated by xs KOH while dissociating hydroxyl ion [i.e., reversing Eq. (g)] in solvents of high dielectric constant such as formamide. The neutral hydroxycarbonyl complex loses COj on warming, whereas its potassium salt is stable in solution even at lOO C ... 

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. 

Other organic amides, such as formamide, A-methylformamide, A-methylaceta-mide, and tetramethylurea, have been investigated as solvents for electrochemical use primarily due to their high dielectric constant none of them, however, seem to offer distinct advantages over DMF or NMP and in some respects they are inferior. N,N-Dimethylacetamide may be purified by destination in vacuum [374]. 

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. 

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. 

An investigation into the co-solvent employed was also carried out [21]. The solvents were selected so that they differed significantly in dielectric constant (fi, indicated by the values in parentheses) dichloromethane (8.9), trifluoroethanol (26.7), acetonitrile (37.5), water (78.4) and formamide (111). The epoxidation of 1-phenylcyclohexene with catalyst (17) was tested using these co-solvents with water in a 1 1 ratio. Epoxidation did not occur in dichloromethane this is perhaps due to the poor miscibility of the two solvents, thus limiting the availability of the inorganic oxidant in the organic phase. No reaction was also observed in formamide. This could be due to the iminium species being too well stabilized/solvated, and the possibility of an irreversible attack by the formamide cannot be dismissed. In trifluoroethanol, the reaction had a similar profile to that in acetonitrile both reactions were complete in 30 min, but the ee was somewhat lower (26% ee in trifluoroethanol and 40% ee in acetonitrile). 

Formamide exhibits a high dielectric constant, is strongly H-bonding, and is a highly organizing solvent. Micelles, and even vesicles, have been obtained in... 

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-... 

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)... 

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