The Individual Acids

Only the racemic form of this acid is obtained from the sugar-alkali reaction. As in the formation of lactic acid, a non-asymmetric enediol is an intermediate in its production (see Section III), and hence the racemate is the sole representative of the four-carbon metasaccharinic acid class. 

Application of the techniques of chromatography and ion exchange, not known to Nef, should greatly simplify the isolation of individual sac-eharinic acids from such mixtures. 

CHiOH-CHa-CHOH-COzH DL-(2,4-Dihydroxybutyrio acid) (phenylhydrazide, m. p., 130-131°) 

Additional evidence regarding the structure of DL-(3-deoxytetronic acid) was obtained (by Nef) by resolution of the acid through the brucine salt. 

One of the two resulting enantiomorphs gave, on oxidation with nitric acid, the enantiomorph of naturally occurring (—)-malic acid. 

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High silicon iron offers excellent resistance to attack by all concentrations of nitric-sulphuric acid mixtures. The mixed acid corrodes the iron at rates never greater and often lower than the individual acids of comparable concentration. 

Figure 9.2. Chromatogram of a seawater extract (20 ml) sample for amino acids collected at 6 m in the Kiel Fjord. The concentrations of the individual acids were quantified as follows (in nmol/1) meto, 11 asp 34.4 thr, 23.2 ser, 88 glu, 36 gly, 100 ala, 56 vol, 16 ileu, 9.6 leu, 12 galactosamine and amino sugars, 4 tyr, 6.8 phe, 7.2 B-ala, 20.8 a-amino-y, 14.4 orn, 44 lys, 12 hist, 7.2 arg, 8.6 cysS02H, 4 cit, trace tan, cys, trace glucose-amine, trace met, trace urea, trace phosphoserine, trace OH-lys, trace. The total concentration of amino acid in the sample lies around 51 q.g/1, assuming a mean molecular weight of 100. Source [264]...

Figure 1.10 Differential heats of adsorption as a function of coverage for ammonia on H-ZSM-5 (o) and H-mordenite ( ) zeolites [70], In both cases, the heats decrease with the extent of NH3 uptake, indicating that the strengths of the individual acidic sites on each catalyst are not uniform. On the other hand, the H-ZSM-5 sample has a smaller total number of acidic sites. Also, the H-mordenite sample has a few very strong sites, as manifested by the high initial adsorption heat at low ammonia coverage. These data point to a significant difference in acidity between the two zeolites. That may account for their different catalytic performance. (Reproduced with permission from Elsevier.)...

The extent to which the pH of a solution is buffered against additions or removals of protons is measured by the solution s pH buffer capacity. This is defined as the amount of strong acid or base required to produce unit change in pH. The buffering depends on the transfer of protons between donors and acceptors, i.e. Bronsted acids and bases, which form conjugate acid-base pairs. The pH buffer capacity of a solution is calculated from the buffer capacities of the individual acid-base pairs present. 

Course A. To calculate the heat of dissociation, AH2, at the decomposition temperature of the individual acid-soaps,... 

Some Effects of Lipolysis. The most serious effect of lipolysis is the appearance of the so-called rancid flavor which becomes detectable in milk when the ADV exceeds 1.2-1.5 mEq/liter (Brathen 1980). The fatty acids and their soaps, which are thought to be implicated in the rancid flavor, have been studied in an effort to assess the role of the individual acids in the overall rancid flavor picture. Scanlan et al (1965) reported that only the even-numbered fatty acids from C4 to Cl2 account for the contribution of fatty acids to the flavor, but that no single acid exerts a predominating influence. Another study has implicated the sodium and/or calcium salts of capric and lauric acids as major contributors to the rancid flavor (Al-Shabibi, et al. 1964). Butyric acid, assumed to be the compound most intimately associated with the flavor, was not singled out in either study as being especially involved. 

QUANTITATIVE ASPECTS. Normally the presence of high quantities of the organic acid is sufficient for diagnosis. However, quantification is sometimes required. To do this, serial amounts of the individual acid must be carried through the derivatization, and a calibration curve set up. The various acids show widely different responses to the argon detector. From the standard curves the amounts can be derived by interpolation. Calculation on the basis of urine dilution must be included as well as the aliquot of the final solution that was taken for injection. The procedure for this is similar to that described for estriol in pregnancy urine. 

HETEROPOLYACIDS. Acids derived mini two or more other acids, under such conditions dial the negative radicals or the individual acids retain their structural identity within the complex radical or molecule formed. The term heteropolvacids is usually restricted to complex acids in which both radicals are derived from oxides, such as phosphomolybdic acid. 

In the analysis of fruit juices, it is important to determine the levels of the individual acids to assess authenticity and quality. A range of these acids can be determined using an enzyme-linked assays and these procedures have been collaboratively tested and published in the IFU compendium of methods (citric no. 22, isocitric no. 54, D-malic no. 64, L-malic no. 21 and D-and L-lactic acids no. 53). r-Biopharm now distributes the Boehringer Mannheim kits to assess the levels of these acids. Similar kits are available from other suppliers. 

It is clear that the levels of the individual acids in rancid milk can be considerably lower than the threshold values reported by Scanlan et al. (1965), which do not include the levels contributed by the fresh milk, (i.e., approximately half the concentrations shown in the second column). Thus, the flavor of the combination of the acids in rancid milk is apparently sufficient to exceed the threshold for detection of rancidity. 

Anhydrides composed of two different acids are called mixed anhydrides and are named by using the names of the individual acids. 

To identify suitable materials for an acid complex such as Hl, one can begin by surveying materials applicable to the individual acid/chemical. Table 4.5 to table 4.7 list the corrosion properties of various materials in I2, HI acid, and H2SO4.12 is a strong oxidizer, especially in liquid form at high temperature. The corrosion rates of a number of corrosion-resistant materials in I2 at 300 and 450°C are listed in table 4.5. Even though the data show that gold and platinum are stable in an I2 environment, they have been found to dissolve in HI. Refractory metals such as Ta and Nb alloys are probably the best candidates within the l2-rich environment in Section 1. 

The individual acids in the acid series are denoted as i and the individual nucleophiles as j thus in the Bronsted equation a series of acids i is varied for a constant nucleophile J. Comhining Eqns. 99 and 100 yields Eqn. 101 ... 

Protonic Acid Media.—As with last year s Report the coverage in this section is incomplete, and more information will be found under those headings dealing with the individual acids. 

As will be shown later, the amount of chemisorbed base can serve as a measure of the number of active catalyst sites. However, besides this quantitative factor which depends on the number of active acidic sites, there is an additional quality factor which is a function of the specific strength of the individual acid sites. Acid strength is determined by bondii forces and is closely concerned with the potential of chemical reactivity. In an acid of the Br0nsted type, the acid strength is determined by the degree of freedom of the proton. Of special significance in the cases discussed here are the experimental results which lead to the... 

Earlier data have indicated that 3-pyridinol is a weaker base than pyridine. A reexamination of these basicities suggests that the reverse is true and that the 3-hydroxyl group is electron releasing here and its introduction increases the basicity of the nitrogen of pyridine and alkylpyridines. pM values for the individual acid dissociation steps for pyridoxamine, pyridoxal, 3-hydroxypyridine-4-carboxaldehyde, and 3-hydroxypyridine-2-carboxaldehyde have been obtained by NMR measurements in Dq 0 solution. ... 

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