Tartaric add

The poly(alkenoic acid)s used in glass polyalkenoate cement are generally similar to those used in zinc polycarboxylate cements. They are homopolymers of acrylic acid and its copolymers with itaconic add, maleic add and other monomers e.g. 3-butene 1,2,3-tricarboxylic add. They have already been described in Section 5.3. The poly(acrylic add) is not always contained in the liquid. Sometimes the dry add is blended with glass powder and the cement is activated by mixing with water or an aqueous solution of tartaric add (McLean, Wilson Prosser, 1984 Prosser et al., 1984). 

Surface faceting may be particularly significant in chiral heterogeneous catalysis, particularly in the N i/P-ketoester system. The adsorption of tartaric add and glutamic acid onto Ni is known to be corrosive and it is also established that modifiers are leached into solution during both the modification and the catalytic reaction [28]. The preferential formation of chiral step-kink arrangements by corrosive adsorption could lead to catalytically active and enantioselective sites at step-kinks with no requirement for the chiral modifier to be present on the surface. 

Stereocontrolled total syntheses of penicillanic acid S. S -dioxide and 6-aminopenicillanic add from (5)-asparatic add and (i ,i )-tartaric add, respectively, have been reported (Eq. 4.37).45... 

Highly enantioselective hydrogenation of / -keto esters is achieved by using a Raney Ni catalyst modified by tartaric add and NaBr (Fig. 32.14) [9, 55]. The catalyst should be prepared under controlled conditions induding suitable pH (3-4), temperature (100°C), and concentration of the modifier (1%) to achieve an optimum stereoselectivity. The addition of NaBr, an achiral modifier, is important. Furthermore, ultrasonic irradiation of the catalyst tends to increase the activity and enantioselectivity [9f,g]. Ultrasonication may remove nonselective sites of the catalyst surface. 

The evidence for the formation of complex heteropoly-acids with tantalic acid is very comparable to that set forth in the case of niobic acid (see p. 165). Solutions of tantalates are readily hydrolysed in aqueous solution by boiling, and even more readily by the addition of mineral acids, acetic acid or succinic acid in the presence, however, of arsenious add, arsenic add, tartaric add or dtric add no precipitation of tantalic add takes place. Again, tincture of galls yields a yellow predpitate with solutions of tantalates which have been rendered feebly acid with sulphuric add this reaction does not, however, take place in the presence of ordinary tartaric add, racemic add or citric acid. Tartaric add also prevents the formation of the predpitates which are thrown down on the addition of potassium ferrocyanide or potassium ferricyanide to faintly acid solutions of tantalates, and hinders the precipitation of tantalic add from solutions in inorganic acids by the action of ammonia. In all these cases it is assumed that complex acids or their salts are produced, in consequence of which the usual reaction does not take place. 

OPTICAL ISOMER- Either of two kinds of optically active three-dimensional isomers (stereoisomers). One kind is represented by mirror-image presence of one or more asymmetric carbon atoms in the compound (glyceraldehyde, lactic acid, sugars, tartaric add, amino acids). The other kind is exemplified by diastereoisomers, which are not mirror images. These occur in compounds having two or more asymmetric carbon atoms thus, such compounds have 2 optical isomers, where n is the number of asymmetric carbon atoms. 

Figure 2 Fischer projections of (a) (2/t,3/Q-tartaric add, (b) (2S,3S)-tartaric add and (c) (2/ ,35)-tartaric acid (meso-...

Several structures of the transition state have been proposed (I.D. Williams, 1984 K.A. Jorgensen, 1987 E.J. Corey, 1990 C S. Takano, 1991). They are compatible with most data, such as the observed stereoselectivity, NMR measurements (M.G. Finn, 1985), and X-ray structures of titanium complexes with tartaric add derivatives (I.D. Williams, 1984). The models, e-g, Jorgensen s and Corey s, are, however, not compatible with each other. One may predict that there is no single dominant Sharpless transition state (as has been found in the similar case of the Wittig reaction see p. 29f.). 

The anhydrous d-tartaric add was obtained from Matheson, Coleman and Bell, East Rutherford, New Jersey. 

Powders with a tartaric acid basis are tested for as follows About 20 grams of the powdered bread are treated with water in a flask of about 200 c.c. capacity on a water-bath, the liquid being concentrated to about 50 c.c., transferred to a separating funnd, acidified with sulphuric add and extracted with ether. The ethereal solution is evaporated in a porcelain dish and the residue heated with a few crystals of resorcinol and one or two drops of concentrated sulphuric acid until white fumes appear the formation of a violet-red coloration indicates the presence of tartaric add. 

So-called effervescing citrates of magnesia are mixtures consisting principally of sugar, tartaric add and sodium bicarbonate in some cases glucose also is present. 

Fixed Acidity.—This is determined by difference. The volatile acidity is multiplied by 1-25 to refer it to tartaric add, the number thus obtained being subtracted from the total acidity calculated as in (1) the remainder represents the fixed acidity in grams of tartaric acid per litre. 

It is sufficient to determine in the two wines those components which are of special interest in relation to the scope of the analysis. If any differences occur, the way in which the wine has been treated will be evident. Thus, if a wine exhibits general and proportional deficiencies of its constituents, mere watering is proved, and the extent of this may be calculated. If, however, as frequently happens, besides watering, addition of tartaric add has occurred, the alcoholic strength will be lowered, but the acidity will not be lowered in the same proportion, and so on. 

Similar to the success achieved with TADDOLs (see Chapter 8) [17], many chiral catalysts and chiral ligands were synthesized from tartaric add, which provides a proper C2-symmetric framework and structural diversity. TaDiAS 1 has remarkable structural diversity because a wide variety of catalysts can be easily synthesized by changing the acetal moieties (R1 and R2), aromatic parts (Ar), and counter anions (X ), making it possible to fine-tune, three-dimensionally, the catalyst (vide infra). Other candidates, such as 2, 3, and 4 (Figure 6.3), produced unsatisfactory results (<10% ee) during preliminary catalyst screening of the N-substituents [4a]. Thus,... 

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