Name: Lactic Acid
CAS No: 2-Hydroxypropionic acid [50-21-5], (R)-(–)-2-Hydroxypropionic acid [10326-41-7], (S)-(þ)-2-Hydroxypropionic acid [79-33-44], (RS)-()-2-Hydroxypropionic acid [598-82-3]
BP: Lactic Acid JP: Lactic Acid PhEur: Lactic Acid USP: Lactic Acid
Acidum lacticum; E270; Eco-Lac; 2-hydroxypropanoic acid; ahydroxypropionic acid; DL-lactic acid; Lexalt L; milk acid; Patlac LA; Purac 88 PH; racemic lactic acid.
2-Hydroxypropionic acid [50-21-5], (R)-(–)-2-Hydroxypropionic acid [10326-41-7], (S)-(þ)-2-Hydroxypropionic acid [79-33-44], (RS)-()-2-Hydroxypropionic acid [598-82-3]
C3H6O3 90.08
Lactic acid is used in beverages, foods, cosmetics, and pharmaceuticals (see Table I) as an acidifying agent and acidulant. In topical formulations, particularly cosmetics, it is used for its softening and conditioning effect on the skin. Lactic acid may also be used in the production of biodegradable polymers and microspheres, such as poly(D-lactic acid), used in drug delivery systems.(1,2) See also Aliphatic Polyesters. Lactic acid is also used as a food preservative. Therapeutically, lactic acid is used in injections, in the form of lactate, as a source of bicarbonate for the treatment of metabolic acidosis; as a spermicidal agent; in pessaries for the treatment of leukorrhea; in infant feeds; and in topical formulations for the treatment of warts.
Lactic acid consists of a mixture of 2-hydroxypropionic acid, its condensation products, such as lactoyllactic acid and other polylactic acids, and water. It is usually in the form of the racemate, (RS)-lactic acid, but in some cases the (S)-(þ)-isomer is predominant. Lactic acid is a practically odorless, colorless or slightly yellowcolored, viscous, hygroscopic, nonvolatile liquid.
See Table II
Boiling point 1228C at 2 kPa (15 mmHg) Dissociation constant pKa = 4.14 at 22.58C Flash point >1108C Heat of combustion 15.13 kJ/kg (3615 cal/kg) Melting point 178C Osmolarity A 2.3% w/v aqueous solution is isoosmotic with serum. Refractive index n D 20 = 1.4251 Solubility Miscible with ethanol (95%), ether, and water; practically insoluble in chloroform. Specific heat 2.11 J/g (0.505 cal/g) at 208C Specific gravity 1.21 Specific rotation [a]D 21 = 2.68 (8% w/v aqueous solution) for (R)- form; þ2.68 (2.5% w/v aqueous solution) for (S)-form. Viscosity (dynamic) 28.5 mPa s (28.5 cP) for 85% aqueous solution at 258C.
Lactic acid is hygroscopic and will form condensation products such as polylactic acids on contact with water. The equilibrium between the polylactic acids and lactic acid is dependent on concentration and temperature. At elevated temperatures lactic acid will form lactide, which is readily hydrolyzed back to lactic acid. Lactic acid should be stored in a well-closed container in a cool, dry place.
Incompatible with oxidizing agents, iodides, and albumin. Reacts violently with hydrofluoric acid and nitric acid
Lactic acid is prepared by the fermentation of carbohydrates, such as glucose, sucrose, and lactose, with Bacillus acidi lacti or related microorganisms. On a commercial scale, whey, corn starch, potatoes, or molasses are used as a source of carbohydrate. Lactic acid may also be prepared synthetically by the reaction between acetaldehyde and carbon monoxide at 130–2008C under high pressure, or by the hydrolysis of hexoses with sodium hydroxide. Lactic acid prepared by the fermentation of sugars is levorotatory; lactic acid prepared synthetically is racemic. However, lactic acid prepared by fermentation becomes dextrorotatory on dilution with water owing to the hydrolysis of (R)-lactic acid lactate to (S)- lactic acid.
Lactic acid occurs in appreciable quantities in the body as an end product of the anaerobic metabolism of carbohydrates and, while harmful in the concentrated form (see Section 15), can be considered nontoxic at the levels at which it is used as an excipient. A 1% v/v solution, for example, is harmless when applied to the skin. There is evidence that neonates have difficulty in metabolizing (R)-lactic acid, and this isomer and the racemate should therefore not be used in foods intended for infants aged less than 3 months old.(3) There is no evidence that lactic acid is carcinogenic, teratogenic, or mutagenic. LD50 (guinea pig, oral): 1.81 g/kg(4) LD50 (mouse, oral): 4.88 g/kg LD50 (mouse, SC): 4.5 g/kg LD50 (rat, oral): 3.73 g/kg
Lactic acid is caustic in concentrated form and can cause burns on contact with the skin and eyes. It is harmful if swallowed, inhaled, or absorbed through the skin. Observe precautions appropriate to the circumstances and quantity of material handled. Eye protection rubber gloves, and respirator are recommended. It is advisable to handle the compound in a chemical fume hood and to avoid repeated or prolonged exposure. Spillages should be diluted with copious quantities of water. In case of excessive inhalation, remove the patient to a well-ventilated environment and seek medical attention. Lactic acid presents no fire or explosion hazard but emits acrid smoke and fumes when heated to decomposition.
GRAS listed. Accepted for use as a food additive in Europe. Included in the FDA Inactive Ingredients Database (IM, IV, and SC injections; oral syrups and tablets; topical and vaginal preparations). Included in medicines licensed in the UK. Included in the Canadian List of Acceptable Non-medicinal Ingredients.
Aliphatic polyesters; sodium lactate.
A specification for lactic acid is contained in the Food Chemicals Codex (FCC).(5) The EINECS number for lactic acid is 200-018-0. The PubChem Compound ID (CID) for lactic acid includes 612, 107689 and 61503.