Lactic acid physical properties

Physical properties. All are colourless crystalline solids except formic acid, acetic acid (m.p. 18 when glacial) and lactic acid (m.p. 18°, usually a syrup). Formic acid (b.p. loo ") and acetic acid (b.p. 118 ) are the only members which are readily volatile lactic acid can be distilled only under reduced pressure. Formic and acetic acids have characteristic pungent odours cinnamic acid has a faint, pleasant and characteristic odour. 

Specific rotation is a physical property of a substance just as melting point boil mg point density and solubility are For example the lactic acid obtained from milk is exclusively a single enantiomer We cite its specific rotation m the form [a]o =+3 8° The temperature m degrees Celsius and the wavelength of light at which the measure ment was made are indicated as superscripts and subscripts respectively... 

Physical Properties. Pure, anhydrous lactic acid is a white, crystalline soHd with a low melting poiat. However, it is difficult to prepare the pure anhydrous form of lactic acid generally, it is available as a dilute or concentrated aqueous solution. The properties of lactic acid and its derivatives have been reviewed (6). A few important physical and thermodynamic properties from this reference are summarized ia Table 1. 

Table 1. Physical and Thermodynamic Properties of Lactic Acid...

Many of the physical properties are not affected by the optical composition, with the important exception of the melting poiat of the crystalline acid, which is estimated to be 52.7—52.8°C for either optically pure isomer, whereas the reported melting poiat of the racemic mixture ranges from 17 to 33°C (6). The boiling poiat of anhydrous lactic acid has been reported by several authors it was primarily obtained duriag fractionation of lactic acid from its self-esterification product, the dimer lactoyUactic acid [26811-96-1]. The difference between the boiling poiats of racemic and optically active isomers of lactic acid is probably very small (6). The uv spectra of lactic acid and dilactide [95-96-5] which is the cycHc anhydride from two lactic acid molecules, as expected show no chromophores at wavelengths above 250 nm, and lactic acid and dilactide have extinction coefficients of 28 and 111 at 215 nm and 225 nm, respectively (9,10). The iafrared spectra of lactic acid and its derivatives have been extensively studied and a summary is available (6). 

DUactide (5) exists as three stereoisomers, depending on the configurations of the lactic acid monomer used. The enantiomeric forms whereia the methyl groups are cis are formed from two identical lactic acid molecules, D- or L-, whereas the dilactide formed from a racemic mixture of lactic acid is the opticaUy iaactive meso form, with methyl groups trans. The physical properties of the enantiomeric dilactide differ from those of the meso form (6), as do the properties of the polymers and copolymers produced from the respective dilactide (23,24). 

Except for their effect on plane-polarized light, two enantiomers of a chiral compound have identical physical properties. For example, the two isomers of lactic acid shown below have the same melting point, 52°C, and density, 1.25 g/mL. 

Lactide (LA), the cyclic diester of lactic acid, has two stereogenic centers and hence exists as three stereoisomers L-lactide (S,S), D-lactide (R,R), and meso-lactide (R,S). In addition, rac-lactide, a commercially available racemic mixture of the (R,R) and (S,S) forms, is also frequently studied. PLA may exhibit several stereoregular architectures (in addition to the non-stereoregular atactic form), namely isotactic, syndiotactic, and heterotactic (Scheme 15). The purely isotactic form may be readily prepared from the ROP of L-LA (or D-LA), assuming that epimerization does not occur during ring opening. The physical properties, and hence medical uses, of the different stereoisomers of PLA and their copolymers vary widely and the reader is directed to several recent reviews for more information.736 740-743... 

Enantiomers have identical chemical and physical properties in the absence of an external chiral influence. This means that 2 and 3 have the same melting point, solubility, chromatographic retention time, infrared spectroscopy (IR), and nuclear magnetic resonance (NMR) spectra. However, there is one property in which chiral compounds differ from achiral compounds and in which enantiomers differ from each other. This property is the direction in which they rotate plane-polarized light, and this is called optical activity or optical rotation. Optical rotation can be interpreted as the outcome of interaction between an enantiomeric compound and polarized light. Thus, enantiomer 3, which rotates plane-polarized light in a clockwise direction, is described as (+)-lactic acid, while enantiomer 2, which has an equal and opposite rotation under the same conditions, is described as (—)-lactic acid. 

These dendrimers expand the repertoire of polymers available for study. Current investigations are primarily limited to linear polymers that possess ill-defined solution structures and fewer hydroxyl groups for further modification. The introduction of biocompatible building blocks (e.g., glycerol and lactic acid) augments the favorable and already known physical properties of dendrimers. These properties are likely to facilitate the design of new materials for specific biomedical and tissue engineering applications. 

The physical properties and melt processing of PLA are similar to those of conventional packaging resins. It may thus be used as a commodity resin for general packaging application. In many aspects the basic properties of PLA lie between those of crystal PS and PET [ 14]. When plasticized by its own monomer lactic acid, PLA becomes increasingly flexible so that products that mimic PVC, LDPE, LLDPE, PP, and PS can be prepared [15]. Possible applications are espe-... 

As you can see from Table 6.3, there are many compounds that have the empirical formula CH20. The substance might be formaldehyde, but it could also be lactic acid (found in milk) or acetic acid (found in vinegar). Neither lactic acid nor acetic acid connect the theft to the suspect. Further information is required to prove that the substance is formaldehyde. Analyzing the physical properties of the substance would help to discover whether it is formaldehyde. Another important piece of information is the molar mass of the substance. Continue reading to find out why. 

Japan s Dainippon Ink and Chemicals (DIC) has pursued the alternate approach of combining polyester and PLA properties into one polymer. DIC developed a biodegradable copolymer called CPLA based on a co-polyester plus lactic acid. A higher ratio of co-polyester increases flexibility, while more lactic acid adds stiffness. One version of CPLA is reported to combine PS-like clarity with PP-like physical properties. 

J )-l-phen ielhylamine to give the R,R salt, and (5)-lactic acid reacts w ith the R aiiiine to give the S,R salt. The two salts are diastereomers they are ditl erent compounds, with different chemical and physical properties. It may therefore be possible to sepeuate them by crystallization or some other means. Once separated, acidification of the two diastereomeric salts with a strong acid then allow s us to isolate the two pure enantiomers of lactic acid and to recover the chiral amine for reuse. 

In 1873 Wislicenus made the suggestion that in compounds like lactic acid and the tartaric acids in which isomers have the same structure but differ in physical properties, e.g.y in their rotation of polarized light, the only explanation is that the atoms of the molecules are dijfer-ently arranged in space. Now, in considering this suggestion in con-... 

One of the most promising applications of polyolefin hybrids is a compatibilizer for blend polymer for polyolefin and non-polyolefin. In Figure 7, TEM micrographs of PP/PMMA and EBR/poly(lactic acid) (PLA) blend polymers with and without polyolefin hybrids as a compatibilizer are displayed. Figure 7(a) represents the phase stracture of a PP/PMMA (62/38 wt%) blend polymer. Since PP and PMMA are immiscible, huge PMMA domains (> 20 pm) exist in the PP matrix. When 5 wt% of PP-g-PMMA (PMMA contents 38 wt%) was added to this blend polymer as a compatibilizer, PMMA domains were finely dispersed as is shown in Figure 7(b). As a result, the physical properties for both FM and FS were drastically enhanced from 35.3 MPa for FS and 1800 MPa for FM to 61.4 MPa for FS and 2200 MPa for FM, respectively. 

Like R and S, d and l indicate the configuration of an asymmetric carbon, but they do not indicate whether the compound rotates polarized light to the right (-h) or to the left (-) (Section 5.7). For example, o-glyceraldehyde is dextrorotatory, whereas D-lactic acid is levorotatory. In other words, optical rotation, like melting or boiling points, is a physical property of a compound, whereas R, S, d, and l are conventions humans use to indicate the configuration of a molecule. 

---