Formamide, 31 Table

It is to be noted that solvent effect on the reaction is rather small e.g., a 12-fold increase in rate was observed on going from THF to dimethyl-formamide (Table V, reactions 2 and 4). Addition of pyridine or PPhj, which may take up the vacant coordination site in the acyl, slows down the reaction by less than a factor of 2 (Table V, reaction 5). Furthermore,... 

Medium effects have already been discussed in sect. 3.6.3. For a majority of substituted ammonium ions the transfer from water to acetonitrile increases pKa by between 7.2 and 7.9 units. The scatter in Api a values is still larger for molecular acids ° because anion peculiarities are not levelled by solvation in acetonitrile. Medium effects are usually more uniform for transfers from acetonitrile to dimethyl-formamide (Table 3.6.1). We expect log for this transfer to be negative since dimethylformamide is more basic than acetonitrile, and we expect log to be close to zero since neither solvent is a good... 

Measurements in the formic acid system were reported by Lawrence and Parsons. The interfacial tension in formic acid (39.90 fiH cm at the electrocapillary maximum) is the highest of any non-aqueous solvent so far investigated. The work of adhesion is correspondingly low in contrast to the high value in formamide (Table 7.1.1). Preferential adsorption of formic acid from aqueous solutions occurs to a similar extent at both the (uncharged) mercury-solution interface and the air-solution interface. The formic acid dipole appears to be preferentially oriented... 

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.

Table 2. Vapor Pressure of Formamide at Various Temperatures ...

The quahty of formamide suppHed by BASE is certified as having a minimum assay of 99.5%. The principal impurities in the material are ammonium formate, methanol, water, and traces of iron. The quaUty of formamide supphed by BASE is certified to meet the specifications given in Table 3. 

Only A/-vinyl-2-pyrrohdinone (VP) [88-12-0] is of significant commercial importance and hence is the principal focus of this article. Vinylcaprolactam is available (BASF) and is growing in importance, and vinyl formamide is available as a developmental monomer (Air Products). Some physical properties are given in Table 1. 

Organic salts (e.g. trimethylammonium benzoate) are usually purified by recrystallisation from polar solvents (e.g. water, ethanol or dimethyl formamide). If the salt is too soluble in a polar solvent, its concentrated solution should be treated dropwise with a miscible nonpolar, or less polar, solvent (see Table 8, Chapter 1) until crystallisation begins. 

Select mobile phases for HPSEC based on their ability to dissolve the sample and their compatibility with the column. Zorbax PSM columns are compatible with a wide variety of organic and aqueous mobile phases (Table 3.4), but analysts should avoid aqueous mobile phases with a pH greater than 8.5. As mentioned earlier, select mobile phases that minimize adsorption between samples and silica-based packings. Sample elution from the column after the permeation volume indicates that adsorption has occurred. If adsorption is observed or suspected, select a mobile phase that will be more strongly adsorbed onto the silica surface than the sample. For example, N,N-dimethyl-formamide (DMF) is often used for polyurethanes and polyacrylonitrile because it eliminates adsorption and dissolves the polymers. When aqueous mobile phases are required, highly polar macromolecules such as Carbowax can be used to coat the silica surface and eliminate adsorption. Table 3.5 provides a list of recommended mobile-phase conditions for some common polymers. 

Table 3.3 Mulliken charges in formamide with different methods...

The equilibrium contact angles for PE and triallyl cyanurate (TAC) grafted PE with water and formamide are presented in Table 7. The grafting of TAC onto PE increases the surface energies of modified PEs [32]. 

Table 7 reveals that the grafting of TAC onto PE decreases the equilibrium contact angles of water and formamide from 92° to 65° and from 75° to 53°, respectively. This decrease is a function of the monomer level and the irradiation dose. At a fixed irradiation dose of 15 Mrad, variation of the TAC level from 0.5 to 3 parts causes a reduction in the contact angles of water by 13° (from 88° to 75°) and of formamide by 11° (from 72° to 61°). This is due to the fact that the concentration of... 

The effect of irradiation of samples in the absence of TAC on the contact angles is also reported in Table 7. Modification of the surface takes place, as is evident from the decrease in the contact angles of water and formamide. The change, which is maximum at an irradiation dose of 10 Mrad, is due to the generation of polar functionalities on the surface. This is also corroborated from the IR/XPS studies described later. The contact angles are lowered further when TAC is incorporated in the system (compare TO/5 with Tl/5, TO/15 with Tl/15, etc.)... 

Chromium aminocarbenes [39] are readily available from the reaction of K2Cr(CO)5 with iminium chlorides [40] or amides and trimethylsilyl chloride [41]. Those from formamides (H on carbene carbon) readily underwent photoreaction with a variety of imines to produce /J-lactams, while those having R-groups (e.g.,Me) on the carbene carbon produced little or no /J-lactam products [13]. The dibenzylaminocarbene complex underwent reaction with high diastereoselectivity (Table 4). As previously observed, cyclic, optically active imines produced /J-lactams with high enantioselectivity, while acyclic, optically active imines induced little asymmetry. An intramolecular version produced an unusual anti-Bredt lactam rather than the expected /J-lactam (Eq. 8) [44]. 

With optically active formamide-derived aminocarbene complexes high enantioselectivity was observed in most cases (Table 5). This chemistry was used in the synthesis of 1-carbacephalathin and 3-ANA precursors (Eq. 9) [48], as well as the synthesis of a,a -disubstituted amino acids (Scheme 1) [49]. 

The diastereoselection of the Diels Alder reaction of methyl acrylate with cyclopentadiene was investigated [74] in microemulsions prepared with isooctane oil, CTAB as surfactant and 1-butanol as cosurfactant, and the results were compared with those found in pure solvents and water (Table 6.12). In emulsions rich in 1-butanol and formamide (entries 1 and 4) the reaction was slow (72 h) and the diastereoselectivity was practically the same as that... 

Table 6.12 Diastereoselectivity of Diels-Alder reaction of methyl acrylate with cyclopentadiene in formamide microemulsion and pure solvents...

Dimethylformamide is also a suitable solvent [50], it has, however, the disadvantage of being oxidized at fairly low potentials to A-acyloxy-iV-methyl formamide [51]. The influence of the composition of the ternary system water/methanol/dimethyl-formamide on the material and current yield has been systematically studied in the electrolysis of co-acetoxy or -acetamido substituted carboxylates [32]. Acetonitrile can also be used, when some water is.added [52]. The influence of various solvents on the ratio of Kolbe to non-Kolbe products is shown in Table 1 [53]. 

Table V. Wetting Angle at the Contact with Water ( fa) and Formamide (- jO and Critical Surface Tension (1 ) at 20°C...

Such one-center enhancement effects can be illustrated by formamide 5 for nb—>7Ta (3.109c) interactions. As shown in Table 3.19, the n — -7tco interaction of 5 leads to strong conjugative stabilization (59.8 kcal mol-1) and reduced C—O bond order (1.732), the famous amide resonance of peptide chemistry ... 

Table 5.16. A comparison ofH-bond energy (AAhb) andNRTbond orders ( ab) for C=0- H—N hydrogen bonds in binary formamide complexes...

Table 5.20. Cooperative (n-dependent) properties of linear formamide chains (see Figs. 5.19 and 5.27), showing the incremental binding energy AEn, average H-bonded Ron and Rmi distances, and partial charges Q and Qn on terminal monomers of the (H2NCHO) chain (for comparison, the cyclic pentamer in Fig. 5.27(c) has Ro u = 1.879 A, Rm = 1-024 A, and average H-bond energy 7.92 heal mol x)...

Preparation of formamides from COz and a non-tertiary amine by homogeneous hydrogenation has been well studied and is extremely efficient (Eq. (12)). Essentially complete conversions and complete selectivity can be obtained (Table 17.3). This process seems more likely to be industrialized than the syntheses of formic acid or formate esters by C02 hydrogenation. The selectivity is excellent, in contrast to the case for alkyl formates, because the amine base which would stabilize the formic acid is used up in the synthesis of the formamide consequently little or no formic acid contaminates the product. The only byproducts that are likely to crop up in industrial application are the methylamines by overreduction of the formamide. This has been observed [96], but not with such high conversion that it could constitute a synthetic route to methylamines. 

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... 

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