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LACTIC ACID

Lactic acid is used in the food industry, in mordant dyeing, in leather production, in fermentation shops as a bactericidal agent, for the production of medicines, plasticizers. Ethyl and butyl lactates are used as solvents for cellulose ethers, drying oils, vegetable oils; butyl lactate - as well as a solvent for some synthetic polymers.

Lactic acid (2-hydroxypropionic acid)
Substance group: Organic acids

Molecular weight 90.1; colorless crystals. Known D (+) -lactic acid, D (-) -lactic (meat-lactic) acid and racemic lactic acid - fermentation lactic acid. For D, L- and D- lactic acids - melting point, respectively, 18 ° C and 53 ° C; boiling point, respectively, 85 ° C / 1 mm Hg. and 103 ° C / 2mm Hg; for D- lactic acid, the specific optical rotation for the D-line of sodium at a temperature of 20˚C: [α] D 20   -2.26 (concentration 1.24% in water). For D, L -lactic acid ∆H 0 formation - 682.45 kJ / mol; ∆H 0 melting 11.35 kJ / mol; ∆H 0 evaporation 110.95 kJ / mol (25 ° C), 65.73 kJ / mol (150 ° C). For L- lactic acid ∆H 0 combustion - 1344.8 kJ / mol; ∆H 0 formation -694.54 kJ / mol; ∆H 0 melting 16.87 kJ / mol.

Due to the high hygroscopicity of lactic acid, its concentrated aqueous solutions are usually used - syrupy, colorless, odorless liquids. For aqueous solutions of lactic acid, the density is g / cm 3 at a temperature of 20˚C d 4 20 1.0959 (40%), 1.1883 (80%), 1.2246 (100%); specific optical rotation for the sodium D-line at a temperature of 25˚С: [α] D 25   1.3718 (37.3%), 1.4244 (88.6%); h 3.09 and 28.5 mPa ∙ s (at 25 ˚С), respectively, for 45.48 and 85.32% solutions; g 46.0.10 -3 N / m (25 ° C) for 1 M solution; e 22 (17 ° C). Lactic acid dissolves in water, ethanol, poorly - in benzene, chloroform, and other halogenated hydrocarbons; pK a 3.862 (at 25 ° C); pH of aqueous solutions 1.23 (37.3%), 0.2 (84.0%).

Oxidation of lactic acid is usually accompanied by decomposition. Under the action of HNO 3 or O 2 of air in the presence of Cu or Fe, HCOOH, CH 3 COOH, (COOH) 2 , CH 3 CHO, CO 2 and pyruvic acid are formed. Reduction of lactic acid HI leads to propionic acid, and reduction in the presence of Re-mobile leads to propylene glycol.

Lactic acid dehydrates to acrylic acid, when heated with HBr, forms 2-bromopropionic acid, when the Ca salt reacts with PCl 5 or SOCl 2 -2-chloropropionyl chloride . In the presence of mineral acids, self-esterification of lactic acid occurs with the formation of lactone, as well as linear polyesters. When lactic acid interacts with alcohols, hydroxy acids RCH 2 CH (OH) COOH are formed, and when lactic acid salts react with alcohol esters. The salts and esters of lactic acid are called lactates.

Lactic acid is formed as a result of lactic acid fermentation (with sour milk, sauerkraut, pickling vegetables, ripening cheese, ensiling feed); D- lactic acid is found in tissues of animals, plants, and also in microorganisms.

In industry, lactic acid is obtained by hydrolysis of 2-chloropropionic acid and its salts (100 ° C) or lactonitrile CH 3 CH (OH) CN (100 ° C, H 2 SO 4 ), followed by the formation of esters, the isolation and hydrolysis of which leads to a high quality. Other methods of producing lactic acid are known: the oxidation of propylene with nitrogen oxides (15-20 ° C) followed by treatment with H 2 SO 4 , the interaction of CH 3 CHO with CO (200 ° C, 20 MPa).

Lactic acid is used in the food industry, in mordant dyeing, in leather production, in fermentation shops as a bactericidal agent, for the production of medicines, plasticizers. Ethyl and butyl lactates are used as solvents for cellulose ethers, drying oils, vegetable oils; butyl lactate - as well as a solvent for some synthetic polymers.

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