O- -Lactic acid

Alpha-gras, n. alfa grass, esparto, -milchsaure, /. (,o -)lactic acid, -naphtol, n. alpha naphthol, a-naphthol (l-naphthol). -strahlen, m.pl. alpha rays, -zellstoff, m. alpha cellulose. Alpranken, f.pl. bittersweet (Solanum dulcamara). 

O Lactic acid, CH3CHOHCOOH, is a monoprotic acid that is produced by muscle activity. It is also produced from milk by the action of bacteria. What is the pH of a 0.12 mol/L solution of lactic acid ... 

H2SO4.3H2O o-terphenyl Toluene - — Phenolphthalain O Ca(N03)2.4H20 A Sucrose O Lactic acid... 

Figure 9.5 Changes in titratable acidity (O), lactic acid ( ) and lactose ( ) on heating homogenized milk in sealed cans at 116°C. Titratable acidity expressed as mg lactic acid/100 g...

Figure 7. Ionization constants of acids in ethanol-water mixtures vs. the dielectric constant function at 25°C. A Malonic acid (O), lactic acid (A), succinic acid ( ). (B) Cyanoacetic acid ( ), salicyclic acid ( ), glutaric acid ( ). C Chloroacetic acid (O), glycolic acid (A), isovaleric acia(D).

Copyrigjiit O WSl Witey-VCH Vef GmbH Co. KGaA ISBNst 3-527-2 093-1 (Hafdb ) 3-527-60085-X (Electronic) j 5 o-Lactic Acid Derivatives... 

The above-mentioned chemical catalytic routes lead to racemic AHA mixtures. For the direct use of LA (or its esters) as a solvent or platform molecule for achiral molecules like acrylic acid and pyruvic acid, stereochemistry does not matter. The properties of the polyester PLA, the major application of LA, however, suffer tremendously if d and l isomers are built in irregularly [28]. This is exemplified by atactic PLA, made from racemic LA, which is an amorphous polymer with low performance and limited application. However, when l- and D-lactic acid are processed separately into their respective isotactic L- and d-PLA, as discovered by Tsuji et al., a stereocomplex is formed upon blending these polymers. This polymer exhibits enhanced mechanical and thermal properties [28, 164]. A productive route to D-Iactic acid is, however, missing today. If the chemocatalytic routes to LA are to become viable, enantiomer resolution of the racemate needs to be performed. Given separation success, a cheap source of o-lactic acid will be unlocked immediately, providing an additional advantage over the fermentation route (cfr. Table 2). 

Lactic acid is a chiral molecule existing as two stereoisomers, l- and o-lactic acid which can be produced by different ways, i.e., biologically or chemically synthesized (Averous 2008). 

In contrast, the chemical process could lead to various ratio of l- and o-lactic acid. Indeed, the chemical reactions leading to the formation of the cychc dimer, the lactide, as an intermediate step to the production of PLA, could lead to macromolecular chains with L- and o-lactic acid monomers. This mechanism of ring-opening polymerization (ROP) from the lactide explains the formation of two enantiomers. This ROP route has... 

Scheme 1.4 shows three lactides consisting of different stereoisomeric lactic acid units, l- and D-lactides consist of two l- and o-lactic acids, respectively, while meso-lactide consists of both d- and L-lactic acids. Racemic lactide (rac-lactide) is an equimolar mixture of d- and L-lactides. The melting points (Tm) of these lactides are compared in Table 1.3. Note that the is higher in rac-lactide and is lower in meso-lactide. 

In some instances, two enantiomers are found in nature, but they are not found together in the same biological system. For example, lactic acid occurs naturally in both forms. The L-lactic acid is found in living muscle, whereas the o-lactic acid is present in sour milk. When we realize that only one enantiomer is found in a given biological system, it is not too surprising to find that the system can usually use or assimilate only one enantiomer. Humans utilize the o-isomers of monosaccharides and are unable to metabolize the L-isomers. The d form of glucose tastes sweet, is nutritious, and is an important component... 

Both L- and o-lactic acid stereoisomers are naturally occurring however, most of the lactic acid in nature is L-type or sometimes racemic. The fact that lactic acid that is produced in the human body is in the L-enantiomeric form and the interest in the biomedical applications of this polymer have led both research and production to concentrate on L-lactide or OL-lactide polymers [16-18]. The o-isomer does not have many applications, except for use in particular medicinal chemicals. 

The two lactic acid isomers shown in Figure 10.15 are labeled o-lactic acid and L-lactic acid (d is for dextro, meaning right l is for levo, meaning left). They might be expected to have quite similar properties, and they do. They have identical melting points, boiling points, and solubilities, for instance. And if we try to prepare lactic add in the... 

Fike R and S, the symbols d and l indicate the configuration of an asymmetric center, but they do not indicate whether the compound rotates the plane of polarization of polarized light to the right (+) or to the left (-) (Section 4.8). For example, o-glyceraldehyde is dextrorotatory, whereas o-lactic acid is levorotatory. In other words, optical rotation, like melting points or boiling points, is a physical property of a compound, whereas R, S, D, and l are conventions humans use to indicate the configuration about an asymmetric center. 

Biosynthetic routes often have product-specific advantages over chemical synthesis, which are important for extending and adding value to some bulk products listed in O Table 1.1. For example, optically active compounds, such as lactic acid, can be produced as either l- or o-lactic acid employing specific species of lactobacilli as biocatalysts, whereas chemical synthesis produces a racemic mixture of d, L-lactic acid. Specific properties of polylactide polymers and chemical derivatives of lactic acid differ importantly depending upon the chirality of the monomer (stereospecificity). 

The modified pseudoreference electrode has been successfully used in construction of NAD-dependent amperometric biosensors for o-lactic acid with the linear response ranging from 0.01 to 2 mM of o-lactic acid and detection limit as low as 0.0025 mM. 

Uuito, I., Juuti, H., ParkMnen, J., et al. Biodegradable self-expanding poly-L/o-lactic acid vascular stent a pilot study in canine and porcine iliac arteries. J. Endovasc. Then Off. J. Int. Soc. Endovasc. Spec. 11, 712-718 (2004). doi 10.1583/04-127MR.l... 

A recent paper reported that lipase-catalyzed ROP of lactide occurred with enantioselection of D-lactide [55]. Here, a new lipase-catalyzed enantioselective oligomerization of an alkyl lactate (RLa) is described (Scheme 7) [53] Novozym 435-catalyzed polycondensation of alkyl o-lactates at 50°C gave oligo (o-lactic acid)s (oligoDLAs) at up to 82% yields with n = 2-7. Primary alkyl lactates of Et-, Pr-, and Bu-, showed a higher reactivity than longer alkyl lactates like Pe-, Hx-, Hp-, and Oc-. A secondary alkyl lactate of BuDLa showed a decreased reactivity. u-Lactates did not show any reactivity, i.e., enantioselection for D-isomers is very strict. 

---