Tartaric acid temperature effects

Two mols, for example, 270 grams, of racemic a-methylphenethylamine base are reacted with one mol (150 grams) of d-tartaric acid, thereby forming dl-a-methylphenethylamine d-tartrate, a neutral salt. The neutral salt thus obtained is fully dissolved by the addition of sufficient, say about 1 liter, of absolute ethanol, and heating to about the boiling point. The solution is then allowed to cool to room temperature with occasional stirring to effect crystallization. The crystals are filtered off and will be found to contain a preponderance of the levo enantiomorph. 

Brownson JRS, Georges C, Larramona G, Jacob A, Delatouche B, Levy-Clement C (2008) Chemistry of tin monosulfide (8-SnS) electrodeposition effects of pH and temperature with tartaric acid. J Electrochem Soc 155 D40-D46... 

Fig. 6. Effect of modifying temperature on EDA with the following modifying reagent and conditions ( ) (+)-erythro-2-methyltartaric acid, pH 5.0 5.2, 0°C (O) (S.S)-tartaric acid, pH 5.0-5.2, 0°C (A) ( + )-2-methyl glutamic acid, pH 5.0, 0°C (O) (S)-valine, isoelectric point, 0 C ( ) (S)-glutamic acid, pH 5.2, 0 C. Reaction conditions MAA (neat), 60"C, 80 100 kg/cm2.

The toxic action of white arsenic has been attributed to its inhibitory action on the oxidative processes,9 partly owing to the effect of the change of pH on the enzyme concerned. Small quantities of arsenious acid reduce the power of suitably prepared extracts of animal tissues to oxidise reduced phenolphthalein. The oxidation of tartaric acid at the ordinary temperature and at 37-5° C. is inhibited by arsenious acid, as also is the respiration and fermentation of yeast,10 but the latter... 

A Raney Ni catalyst modified by tartaric acid and NaBr is fairly effective for enantioselective hydrogenation of a series of (3-keto esters (Scheme 1.41) [203a,214,215]. The enantio-discrimi-nation ability of the catalyst is highly dependent on the preparation conditions such as pH (3—4), temperature (100°C), and concentration of the modifier (1%). Addition of NaBr as a second modifier is also crucial. Ultrasonic irradiation of the catalyst leads to even better activity and enantioselectivity up to 98% ee [214d-f. The Ni catalyst is considered to consist of a stable, selective and weak, nonselective surface area, while the latter is selectively removed by ultrasonication. 

Before dyeing with oxidation dyes, the furs are treated with the appropriate killing agents and then mordanted with metal salts. Iron, chromium, and copper salts, alone or in combination, are used for mordanting, and the uptake process requires several hours. Adjustment of the pH is effected with formic, acetic, or tartaric acid. The final dyeing process is carried out in paddles with the precursors and hydrogen peroxide until the actual dye lake is developed and adsorbed within the hair fiber. It takes quite a few hours at room temperature until the dyeing process is finished. 

We have developed a stable CAB 2 (R = aryl) complex that can be prepared in situ by mixing tartaric acid derivative and arylboronic acid at room temperature. In contrast with 2, R = H, which is both air- and moisture-sensitive, the B-alkylated catalyst 2, R = aryl or alkyl, is stable and can be stored in closed containers at room temperature (Eq. 39). A solution of the catalyst (20 mol %) is effective in catalyzing the hetero Diels-Alder reaction of aldehydes with a Danishefsky diene to produce dihydro-pyrone derivatives of high optical purity (up to 98 % ee) (Eq. 40) [39]. The extent of asymmetric induction is largely dependent on the structure of the boronic acid. In general, bulky phenylboronic acid (R = 2,4,6-Me3CeH2, o-MeOC6H4) results in excellent asymmetric induction. 

Several arylboronic acids have been examined in place of borane-THF to improve the Lewis acidity of 2 and the stereoselectivity [49b]. The boron substituent of 2 has a large effect on the chemical yield and the enantiomeric excess of the allylation adduct, and 3,5-bistrifluoromethylbenzeneboronic acid results in the greatest reactivity— when a complex which is easily prepared from a tartaric acid derivative and 3,5-bistri-fluoromethylbenzeneboronic acid in propionitrile at room temperature is used, the reactivity is improved without reducing the enantioselectivity. For instance, the reaction of l-trimethylsilyl-2-methyl-2-propene with benzaldehyde in the presence of only 10 mol % 2 proceeds to give 99 % yield and 88 % ee (Fig. 19). 

The procedure is discussed in detail by Delmon et al.(82-84). The crucial step appears to be the rapid dehydration of the starting solution before any of the components can crystallize out of solution separately. Delmon(85) suggests that a rotary vacuum evaporation would be an effective method of drying the precursor. The actual structure of the precursor is not well defined, but appears to require at least one equivalent of citrate ion per mol of metal ion(83), as presumably the citrate complexes all the metal species in so Iution. The resulting powder patterns, after annealing, indicated no contamination. Delmon(J3) suggests that any multifunctional acid containing at least one carboxyl and one hydroxyl function may be effective. Experiments with tartaric acid on the iron/chromium system produced results similar to citric acid a calcination temperature of 500°C was necessary before crystallization occurred. 

Examples of (a) are quite common and of (b) much less common. A few are shown in Table 1. It should be observed that there are numerous d-d and d-l pairs reported as melting as the same temperature, as for example the diethyl esters of d- and tartaric acid (M.P. 17 °C). Where the chiral centre is sequestered within the molecule, and has httle or no influence on the packing shape, differences of packing energy may well be too small to be measured except under the most refined conditions (see also Section 1.12). The effects of chemical contamination must in any case put in doubt the interpretation of small differences in the search for evidence of discrimination. 

Tartaric acid is one of the most prevalent acids in unripe grapes and mnst. Indeed, at the end of the vegetative growth phase, concentrations in unripe grapes may be as high as 15 g/1. In musts from northerly vineyards, concentrations are often over 6 g/1 whereas, in the south, they may be as low as 2-3 g/1 since combustion is more effective when the grape bunches are maintained at high temperatures. 

The effectiveness of enantioselective hydrogenations on chiral modified RNi catalysts depends on many factors. It is influenced by variables of modification procedure, pH of solution modifier, structure of modifier, concentration of modifier, temperature of solution, period of action of modified solution, and presence of additional components. In the case of modifier (2R, 3R)-tartaric acid, it proved very important to add NaBr into the modifying solution. The amount of TA adsorbed on the catalyst determined the effectiveness of the resulting MRNi catalyst... 

---