Acid and Amine Values

Linear peptides will have free amino- and carboxy- terminal groups. Thus they will exhibit titration curves similar to a free amino acid, but with the pKa values shifted closer to simple acid and amine values (there will be no charge stabilization). 

It is worth noting that a full pH range scan for an equimolar proportion of acid and amine, i.e., a horizontal cut in the middle of the map, would result in a similar double transition, with an extremely wide central region with WII phase behavior and precipitated catanionic species, with two Will bands at high and low pH, and eventually a small WI region at extreme high and low pH values. 

ASTM 2076-92, Standard Test Methods for Acid Value and Amine Value of Fatty Ammonium Chlorides, ASTM, Philadelphia, PA, 1992. 

Abstract—Inconnection with previous papers [1,2] some investigations were carried out of dielectric polarization of complexes composed of carboxylic acids and amines in order to establish a relationship between their polarity and pl value of acidic component. 

Overall, a large variability in Koc values was observed, especially for the more polar compounds. For relatively nonpolar esters, Koc was considered a useful model for sorption to soil with high organic carbon and low clay content, with variation by a factor of 3-5. Significant correlations between Koc and molecular size, self polarizability, and MCIs were observed. For polar acids and amines, Koc values varied up to two orders of magnitude, and poor correlations were obtained for most of the parameters examined. 

Probably the occurrence of this limiting value means that the long chains are orientated in the surface, so that the structure of the surfaces of the hydrocarbons, acids, and amines is practically the same, both in the arrangement of molecules and in the motions of the molecules. The orientation may be approximately perpendicular to the surface, but all that can be definitely stated is that it is probably the same for all the compounds. 

Sections 3.3.1 and 4.2.1 dealt with Bronsted acid/base equilibria in which the solvent itself is involved in the chemical reaction as either an acid or a base. This Section describes some examples of solvent effects on proton-transfer (PT) reactions in which the solvent does not intervene directly as a reaction partner. New interest in the investigation of such acid/base equilibria in non-aqueous solvents has been generated by the pioneering work of Barrow et al. [164]. He studied the acid/base reactions between carboxylic acids and amines in tetra- and trichloromethane. A more recent compilation of Bronsted acid/base equilibrium constants, determined in up to twelve dipolar aprotic solvents, demonstrates the appreciable solvent influence on acid ionization constants [264]. For example, the p.Ka value of benzoic acid varies from 4.2 in water, 11.0 in dimethyl sulfoxide, 12.3 in A,A-dimethylformamide, up to 20.7 in acetonitrile, that is by about 16 powers of ten [264]. 

When carboxylic acids are treated with ammonia or amines, salts are obtained. The salts of ammonia or primary or secondary amines can be pyrolyzed to give amides, but the method is less convenient than 16-72, 16-73, and 16-75 and is seldom of preparative value. Heating in the presence of a base such as hex-amethyldisilazide makes the amide-forming process more efficient. " Boronic acids catalyze the direct conversion of carboxylic acid and amine to amides. 

The first three descriptors have been plotted for 27 amines that have similar values in the remaining two dimensions. Carboxylic acids form a tight cluster near, but separate from, the esters. Alcohols are farther away from the acids, and amines are even farther. Aliphatics are widely separated from aromatics. The formation of these clusters is typical and is what justifies calling these dimensions chemical functionality descriptors. ... 

Fig. 1. The R, values in paper chromatography for the protein amino acids including cystine and for a-aminobutyric acid. I. Solvent butanol-acetic acid-water (12 3 5), 2. solvent phenol-water-conc. NH, aq (120 30 1). I, Alanine 2, a-aminobutyric acid 3, arginine 4, asparagine 5. aspartic acid 6, cysteine 7, cystine 8, glutamic acid 9, glutamine 10, glycine II, histidine 12, isoleucine 13, leucine 14, lysine 15, methionine 16, phenylalanine 17, proline 18, serine 19, threonine 20, tryptophan 21, tyrosine 22, valine. I, Area for acid amino acids II, area for neutral amino acids III, area for basic amino acids and amines.

Inhibition of spontaneous polymerization of (meth) acrylates is necessary not only at their storage but also in the conditions of their synthesis proceeding in the presence of sulfuric acid. In this case, monomer stabilization is more urgent, since sulfuric acid not only deactivates mat r inhibitors but also is capable of intensifying polymer formation. The concentration dependence of induction periods in these conditions has a brightly expressed nonlinear character. And, unlike polymerization in bulk, decomposition of polymeric peroxides is observed at relatively low temperatures in the presence of sulfuric acid, and the values [X] of the amines studied are by ca. 10 times lower than [HQ]. ... 

A number of the methods which depend on pK-values, including paper electrophoresis and ion-exchange chromatography, provide clear results for the derivatives of neutral a-amino acids. For derivatives of P-and y-amino acids and amines this is not necessarily the case. The lability towards acid is also indicative, but it is not easy to exploit it in quantitative measurements. 

In principle it should be possible to obtain more accurate values of AH by calorimetric measurements AS° can then be obtained by combining AH with an accurate measurement of K at a single temperature, and ACp follows if AH has been measured at more than one temperature. Extensive work of this kind has been recently carried out by Christensen and his collaborators for carboxylic acids and amines in water. However, the calorimetric method also has its pitfalls, since a series of apparently accurate measurements for phenols, anilines, and benzoic acids were subsequently deemed unreliable on the basis of a comparison with dissociation constants measured spectrophotometrically over a range of temperatures. 

D 2076-64 (Reapproved 1987) Acid Value and Amine Value of Fatty Quaternary Ammonium Chlorides D 2078-86 Iodine Value of Fatty Quaternary Ammonium Chlorides D 2080-64 Average Molecular Weight of Fatty Quaternary Ammonium Chlorides... 

These tables include all organic and inorganic ligands for which reliable values have been reported in the literature. The present volume is restricted to organic ligands other than amino acids and amines. 

Figure 12.6 Pictures of aqueous dispersions of carbojylic acid- and amine-functionalized CNCs at different pH values, indicating the gelation of the material upon neutralizing the respective functional g oups. Adapted with permission from A. E. Way, L. Hsu, K. Shanmuganathan, C. Weder and S. J. Rowan, ACS Macro Lett, 2012, 1, 1001-1006, Copyright 2012 American Chemical Society.

The dissociation constants of amino acids can be determined, for example, by titration of the acid. Figure 1.2 shows titration curves for glycine, histidine and aspartic acid. Table 1.2 lists the dissociation constants for some amino acids. In amino acids the acidity of the carboxyl group is higher and the basicity of the amino group lower than in the corresponding carboxylic acids and amines (cf. pK values for propionic acid, 2-propylamine and alanine). As illustrated by the comparison of pK values of 2-aminopropionic acid (alanine) and 3-aminopropionic acid ( 3-alanine), the pK is influenced by the distance between the two functional groups. 

Ka and Kai characterize the basic and acidic properties of the mixture (A° + A + ), which is regarded as being a sole species. The approximation to be achieved is evident. The pH value cannot be too far from the neutrality since the carboxylic and amine groups are both functions that are the vehicle of a weak acidity or basicity. Moreover, when equilibria are attained in solution, it may exist as concentrations approximately equal in undissociated carboxylic acid and amine functions, since their analytical concentrations are identical. In these conditions, the concentrations [H3O+] and [OH ] are negligible in Eq. (5.18). Hence,... 

Volatile corrosion inhibitors (VCIs), also called vapor phase inhibitors (VPIs), are compoimds transported in a closed environment to the site of corrosion by volatilization from a source. In boilers, volatile basic compounds, such as morpholine or hydrazine, are transported with steam to prevent corrosion in condenser tubes by neutralizing acidic carbon dioxide or by shifting surface pH toward less acidic and corrosive values. In closed vapor spaces, such as shipping containers, volatile solids such as salts of dicyclohexylamine, cyclohexylamine, and hexamethylene-amine are used. On contact with the metal surface, the vapor of these salts condenses and is hydrolyzed by any moisture to liberate protective ions. It is desirable, for an efficient VCI, to provide inhibition rapidly and to last for long periods. Both qualities depend on the volatility of these compounds, fast action wanting high volatility, whereas enduring protection requires low volatility. 

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