Formic acid, interaction with water

The band at 1721 cm-1 may be due to the C = 0 stretching vibration of a carboxylic acid or ester. This band is observed in pure formic acid and in pure methyl formate at 1730 cm -1 [70]. The slight shift to lower frequency can be due to interaction with water. 

Zharov, V. T. Pervukhin, O. K. Structure of liquid-vapor equilibrium diagrams in systems with chemical interaction. II. Methanol-formic acid—methyl formate—water system. Zh. Fiz. Khim. 1972, 46, 1970-1973. 

The LLE data of the ternary system composed of water + formic acid+ cumene were measured at different temperatures of 298.15, 303.15, and 308.15. The equihbrium data of the ternary mixture were also predicted by the UNIFAC method. It was found that UNIFAC with original group interaction parameters developed for LLE did not provide good prediction. The average RMSD value between the observed and calculated mole fractions with a reasonable error was 8.14% for the UNIFAC model. The solubility of water in cumene increases with amounts of formic acid added to water + cumene mixture. 

The IPA system does not require a co-solvent, but one can be used if this proves advantageous. In the TEAF system a solvent is normally used, though neat TEAF or formic acid can be used if required. The solvent can have a large effect on the reaction rate and optical purity of the product this may in part be because the substrate seems to bind by weak electrostatic interactions with the catalyst, and is also partly due to the pH of the system. Solvents have a dramatic effect on the ionization of formic acid for example, in water the piCa is 3.7, but in DMF it is 11.5. This is because formation of the formate anion becomes less favorable with less polar solvents (see Table 35.2). The piCa of triethy-lamine is far less sensitive. As a consequence, formic acid and triethylamine may remain unreacted and not form a salt. The variation in formic acid piCa can also have a significant impact on the catalyst and substrate, particularly when this is an imine. 

The separation of synthetic red pigments has been optimized for HPTLC separation. The structures of the pigments are listed in Table 3.1. Separations were carried out on silica HPTLC plates in presaturated chambers. Three initial mobile-phase systems were applied for the optimization A = n-butanol-formic acid (100+1) B = ethyl acetate C = THF-water (9+1). The optimal ratios of mobile phases were 5.0 A, 5.0 B and 9.0 for the prisma model and 5.0 A, 7.2 B and 10.3 C for the simplex model. The parameters of equations describing the linear and nonlinear dependence of the retention on the composition of the mobile phase are compiled in Table 3.2. It was concluded from the results that both the prisma model and the simplex method are suitable for the optimization of the separation of these red pigments. Multivariate regression analysis indicated that the components of the mobile phase interact with each other [79],... 

Besides water, other solvent molecules have been investigated to a small extent in connection with anion solvation. We mention here two examples of solvation by formic acid, concerning the ions Cl- 230> and CIO4 235). In the first case coordination numbers up to four were considered. For the one to one complexes the energy of interaction is larger for Cl- than for CIO4. 

Acylaminobiguanides are cyclised by alkalis without difficulty, with loss of water, to 5-guanidino-l,2,4-triazoles. Their interaction with formic acid affords the expected guanamines in the majority of examples 391, 392) (see also Section VII, I). Contrary to a previous claim 91), isonicotinic acid hydrazide dihydrochloride and cyanoguanidine do not give the biguanide under neutral conditions, but form merely a molecular adduct of the reactants 416). 

Another recent example of the question of the formation of intermediate metal-C02 complexes in these reactions was the theoretical study by Ohnishi et al. [84] of the hydrogenation of C02 to formic acid by Ru catalysts. In the presence of water, there was no direct metal coordination of C02, but formation of adducts in which the C and O atoms of C02 interacted with the H (hydride) ligand and the H atom of H20 rfs-Ru(H)2(PMe3)3(H20)(C02). In the absence of water molecules,... 

Song and Naidong [129] analyzed omeprazole and 5-hydroxyomepra-zole in human plasma using hydrophilic interaction chromatography with tandem mass spectrometry. Omeprazole and its metabolite 5-hydroxy omeprazole and the internal standard desoxyomeprazole were extracted from 0.05 ml of human plasma using 0.5 ml of ethyl acetate in a 96-well plate. A portion (0.1 ml) of the ethyl acetate extract was diluted with 0.4 ml of acetonitrile and 10 /il was injected onto a Betasil silica column (5 cm x 3 mm, 5 /rm) and detected by atmospheric pressure ionization 3000 and 4000 with positive electrospray ionization. Mobile phase with linear gradient elution consists of acetonitrile, water, and formic acid (from 95 5 0.1 to 73.5 26.5 0.1 in 2 min). The flow-rate was 1.5 ml/min with total rim time of 2.75 min. The method was validated for a low limit of quantitation at 2.5 ng/ml for both analytes. The method was also validated for specificity, reproducibility, stability, and recovery. 

In some cases, strange approximations were applied in order to circumvent the problems connected with large systems. The interaction energy of the antibiotic tetranactin with an ammonium ion was calculated by replacing the tetranactin by four formaldehyde and four water molecules 158). In an improved study the tetranactin was approximated by using formic acid, ethane, propane and methanol molecules 159>. In an other study [18] crown-6 was simulated by three dimethyl ether molecules 160). 

A marked decrease, compared to water, in lyophobic interactions towards the nonpolar residues of the protein. Of the common strongly protic liquids, only hydrofluoric acid, formic acid, and hydrazine are not completely miscible with simple hydrocarbons, while the others, such as ethylenediamine, dichloroacetic and trifluoroacetic acids, are completely miscible with them. Even in the cases of hydrofluoric acid, formic acid, and hydrazine, the solubility of hydrocarbons is much greater than in water. Thus, a satmated solution of benzene in formic acid at 25°C contains 0.088 mole fraction of benzene, compared to 0.00035 mole fraction of benzene in water (see Section IV,B,3 and Table IV). 

Except for the formic acid extraction, < all the other methods yielded approximately the same amount of polysaccharide. However, even after more than 20 successive extractions of a Swiss brown-earth (Braunerde) with acid, water, and alkali, further extracts gave a positive anthrone reaction for sugars. " The extraction of polysaccharides is probably made difficult by their interaction with inorganic surfaces and humic substances. 

Compounds that are strongly water soluble, such as H2O2, HO2, and to some extent OH radicals together with HCHO (formaldehyde) and certain constituents to be oxidized such as SO2 and carboxylic acids, are incoiporated into the liquid phase. This process leaves behind in the gas phase the less-soluble components such as NO, CO, and CH4. HO2 participates in the liquid phase in an O3 destruction cycle, leading to the formation of formic acid, HCOOH. In the water phase OH reacts with CH2O and HCOOH to form HO /O . These radicals are especially important in the aquatic atmosphere because they interact with Fe(II), Fe(III), and their complexes to produce H2O2, which, in turn, oxidizes aqueous SO2 (see also Figure 12.3e) ... 

A typical mobile-phase composition is an acetonitrile-water gradient with a fixed concentration of trifluoroacetic acid (TFA), formic, or acetic acid (typically 0.05-0.5%). TFA acts as an ion-pairing agent and masks secondary interactions with the silica-based stationary phase. TFA may significantly suppress the ESI response in positive-ion mode. To avoid this, either formic acid is preferred or a mixture of 0.02% TFA and 0.5% acetic acid can be used. Some silica-based RPLC materials can be used with a lower TFA concentration (PepMap ). Alternatively, poly(styrene-divinylbenzene) polymeric materials (PS-DVB) can be applied. With a monolithic PS-DVB column, only a small decrease in separation efficiency on the monolithic column was observed when the TFA concentration was reduced from 0.2%to0.05%[51]. 

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