Acidity in different solvents

Femandez-Garcfa J.C., Orgiles-Barcelo, and A.C., Martm-Martmez J.M., 1991, Halogenation of styrene-butadiene rubber to improve its adhesion to polyurethanes, J. Adhes. Sci Technol, 5, 1065-1080. Oldfield D. and Symes T.E.F., 1983, Surface modification of elastomers for bonding, J. Adhes., 16, 77-96. Pastor-Bias M.M., Ferrandiz-Gomez T.P., and Martm-Martmez J.M., 2000, Chlorination of vulcanized styrene-butadiene rubber using solutions of trichloroisocyanuric acid in different solvents, J. Adhes. Sci. Technol, 14, 561-581. 

TABLE 7.2 Effects of the Lewis Acid in Different Solvents for Reaction (1)... 

Resolution of racemic 1,3/4/6,7,llb-hexahydro-2H-pyrazino[l,2-a]iso-quinolin-4-one into enantiomers was unsuccessful either through the crystallization of diastereomeric chiral salts prepared from enantiopure acids in different solvent mixtures, or with kinetic resolution by an enzymatic acylation using different enzymes (08EJO895). 

TABLE 7.9 Comparison of p/fa Values of Several Acids in Different Solvents... 

It must be stressed that the above agreement between the predicted and experimental values for pRa as a function of medium changes is an exceptional case. The reasons for this are two-fold. First, there is a paucity of thermodynamic measurements (5AGtr) for organic acids and their conjugate bases. Secondly, there is at present considerable doubt as to the validity of p/Ca values measured in different solvents. These doubts arise because of variations in apparent orders of acidity in different solvents and the observations of anomalous types of ionization behaviour in a number of systems. 

Additionally, examination of pKa values in DMSO and mixtures of DMSO with hydroxylic solvents, as obtained by different methods, has revealed considerable variation. This is illustrated in Table 6 for two compounds frequently used as anchors for acidity function scales. If one is to correlate pATa values with thermodynamic transfer functions [eqn (6)], rationalize varying orders of acidity in different solvents (Table 6), or use them inBr nsted relationships (Section 3),... 

Acidity constants always compare the acidity of a proton donator with the basicity of the solvent. Therefore, only acidity constants relating to the same solvent can be compared [iii, iv]. The acidity constant strongly depends on the dielectric constant of the solvent and solvent-solute interaction parameters. About relations between the acidity constants of one acid in different solvents see reference [v]. 

Recently, Blackmond (Klussmann et al. 2006) and Hayashi (Hayashi et al. 2006) investigated the solid-liquid equilibrium of scalemic amino acids in different solvents and the consequences for catalysis. The most striking example, serine, has its eutectic at >99% ee, with the practical consequence that an almost racemic sample can provide an almost enantiopure solution in the solid-liquid equilibrium. It is also known that trituration can influence enantiomeric and diastereomeric compo-... 

At this point, we can only refer to the various acidity scales for different series of solvents, such as those of Hammett [15] and Grunwald [16]. The acidity functions are introduced in order to obtain expressions that are not affected by the relative permittivity and that allow a quantitative comparison of acidity in different solvents. It should be stated, however, that there exists no single scale of acidity or basicity that is universally valid in all types of solvents and appHcable to both equilibrium and kinetic situations [17, 109]. 

Elias et al.82-84) and Yamada et al.87,88 have independently reported that an isokinetic relationship exists between (AHf - AH ) and (AS - ASg) in the free radical polymerization of methyl methacrylate and methacrylic acid in different solvents ... 

This expression means that the values of pAM and the H0 values obtained for the standard solutions should coincide in the case when the primary medium effects for acid and base are the same, i.e. log y0 BH+ - log 7o,b = 0. Practical investigations of proton acidity in different solvents gives the evidence that this is not usually the case [50]. 

Figure 1.12 Solubility of adipic acid in different solvents. (Reprinted with permissions from S. Decker, W.P. Fan, and A.S. Myerson (1986), Solvent Selection and Batch Crystallization, Ind. Eng. Chem. Fund. 25, 925. 1986 American Chemical Society.)...

The solutions of HCl and HOSO3CH3 in aliphatic alcohol (i.e., C H2 +iOH) - normal alcohol C1-C5 and isomeric alcohol C3-C5 have been studied. If the components taking part in resolvation process are capable of H-bonding, the anion solvation by these components cannot be neglected. The differenees in K s values for both acids in different solvents may be explained as follows. 

Figure 6. C-resoncmces of the pterldine part of folic acid in different solvents.

The stability of the hydronium ion determines the pH of water or that of other acids dissolved in water. This changes when we compare the acidity in different solvents. Neat acids such as HF and H2SO4 are much more acidic than when they are dissolved in water. This is because different protonated species are present. For HF dissolved in HF there is the equilibrium... 

Although separation factors between conjugated bile acids are not as good in thin-layer as in paper chromatography, the thin-layer method has been much more used in recent years because of its greater simplicity and speed. The mobilities of common conjugated bile acids in different solvent systems are given in Table IV. It should be observed that several systems can be used in two-dimensional development. 

Table 175. Solubility of some amino acids in different solvents Moles per liter at 25° C ...

Figure 6 Rf values of 2- ubstituted benzoic acids in different solvents. The solvent composition organic componentAvater (40 60 v/v) with addition of 0.1 M tetramethyl ammonium bromide (pK value in parentheses) O, tenzoic acid (4,19) , 2-hydroxy (2,97) , 2-acetoxy (3.5) , 2-carboxy (2.91/5.59) , 2-nitro (2.16) , 2-methyl (3.91) A, 2-amino (6.97) T, 2-chloro (2.92). (From Ref. 162, by permission of Friedr. Viewig and Sohn.)...

A quantum-chemical study of the mechanism of the condensation reaction between propanoic acid and aniline has been made. The mechanism of proton-transfer reactions of 3,5-dinitrosalicylic acid (41) has been the subject of a review (50 references). A successful correlation has been obtained between dissociation of a variety of acids in different solvents and quantum self-similarity measures of the CO2H fragment. The substituent effects of the isopropyl group in 2- (42), 3- (43), and 4-isopropylbenzoic acid (44) have been evaluated from their enthalpies of formation, gas-phase acidities, acidities in MeOH and in DMSO, and their IR spectra in tetrachloromethane. Particular attention was given to the influence of variable conformation on the observed steric effect. In contrast to 2-r-butylbenzoic acid and similarly to 2-methylbenzoic acid, 2-isopropylbenzoic acid exists in two planar conformations (42a,b) in equilibrium. Owing to this conformational freedom, the... 

Dalman LH (1937) Ternary systems of urea and acids. IV. U rea, citric acid and water. V. U rea, acetic acid and water. VI. Urea, tartaric acid and water. J Am Chem Soc 59 775-779 Apelblat A, Manzurola E (1987) Solubility of oxalic, malonic, succinic, adipic, maleic, malic, citric, and tartaric acids in water from 278.15 K to 338.15 K. J Chem Thermodyn 19 317-320 Yang H, Wang J (2011) Solubilities of 3-carboxy-3-hydroxypentanedioic acid in ethanol, butan-l-ol, water, acetone, and methylbenzene. J Chem Eng Data 56 1449-1451 Daneshfar A, Baghlami M, Sarabi RS, Sahraei R, Abassi A, Kariyan H, Khezeli T (2012) Solubility of citric, malonic, and malic acids in different solvents from 303.2-333.2 K. Fluid Phase Equilib 313 11-15... 

Pastor-Bias MM, Ferrandiz-Gomez TP, Martin-Martmez JM (2000) Chlorination of vulcanized styrene-butadiene rubber using solutions of trichloroiso-cyanuric acid in different solvents. J Adhes Sci Technol 14 561... 

Enthalpies and entropies of activation for the decarboxylation of oxalic, malonic, and acetic acids are listed in Table 1 and are shown separately on the isokinetic plots in Fig. 8. Linear trends are observed for (1) aqueous acetic acid and sodium acetate in the presence of various catalysts (2) aqueous oxalic acid at several pH values (3) oxalic acid in different solvents and (4) malonic acid in different solvents and in aqueous solutions having a different pH. Note that the isokinetic trend for the decarboxylation of malonic acid in aqueous solutions at various pH is identical to that for the reaction in nonaqueous solvents, i.e., there is one isokinetic trend for malonic acid. Moreover, the effect of pH on the activation parameters for the decarboxylation of malonic acid in aqueous solution is minimal. On the other hand, the activation data for the decarboxylation of oxalic acid in aqueous solutions determined by Crossey (1991) do not follow the same isokinetic trend as do the corresponding data for this reaction in other solvents. By contrast, activation data calculated from the rate constants determined by Dinglinger and Schroer (1937) for oxalic acid in water (pH 0.5) fall on the isokinetic trend set by the decarboxylation of oxalic acid in nonaqueous solvents, as well as the rate data determined by Lapidus et al. (1964) in the vapor phase. The cause of the disparity between the isokinetic relationships determined by Crossey (1991) and the remainder of the oxalic acid results requires further investigation. The reaction could have been surface-catalyzed, but this is doubtful because some of the oxalic acid... 

---