Mandelic acid, ionization

The phase-diagrams for a number of ternary systems involving mandelic acid, C Hg CH(OH) COjH, were studied by 2 oss 8). who thereby was able to establish the compositions of a variety of interesting acid salts from racemic and optically-active forms of this acid. Strictly speaking, an acid salt MHXj exists only in the solid state, for in solution it breaks down into free acid and the ionized salt M+X. ... 

Styrene may be analyzed by GC, nsing a flame ionization detector. Air analysis may be performed by charcoal adsorption, followed by desorption of the analyte with carbon disnl-fide and injection of the elnant into GC-FID (NIOSH Method 1501 see Section 26.2). Styrene intake in the body may be estimated by analyzing mandelic acid in the nrine by liquid chromatography, polarography, or GC. However, the presence of other aromatics may interfere, as these componnds also generate the same urinary metabolite. Styrene in exhaled air may be analyzed by absorption over ethanol or charcoal followed by GC, UV, or IR analysis. 

Suitable acids for this experiment are acetic acid, succinic acid, benzoic acid, mandelic acid. Weak polybasic acids e.g. succinic add), in the dilutions employed here, act electrically as monobasic acids, i.e. only one hydrogen atom is ionized. 

Thus, in terms of stereochemical theory, the minimal requirement for the differentiation of enantiomers by a chiral reagent is a one-point approach rather than a three-point attachment . This idea is illuminated by the data cited earlier for the heats of neutralization between the base, a-phenylethylamine, and mandelic add. Here the reaction does not involve a covalent bond formation rather it is an ionization leading to an electrostatic situation. For the neutralization of (R )-base with (/ )-acid, — AH = 7.630 0.013 kcal/mol for (/ )-base with (S)-acid, —AH = 7.431 0.014 kcal/mol—a significant difference of approx. 0.2 kcal/mol. 

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