LACTIC ACID

Lactic acid is an organic acid with the molecular formula C3H6O3. 
In its solid state, Lactic acid is white and miscible with water.
When dissolved, Lactic acid forms a colorless solution. Production includes both artificial synthesis and natural sources. 

CAS:    50-21-5
MF:    C3H6O3
MW:    90.08
EINECS:    200-018-0

Synonyms
DL-ALPHA-HYDROXYPROPIONIC ACID;DL-Lactic acid, ACS reagent, 85+%;dl-lactic acid, acs;LACTICACID,RACEMIC,USP;2-Hydroxy-2-methylacetic acid;Biolac;Chem-Cast;E 270

Lactic acid is an alpha-hydroxy acid (AHA) due to the presence of a hydroxyl group adjacent to the carboxyl group. 
Lactic acid is a synthetic intermediate in many organic synthesis industries and in various biochemical industries. 
The conjugate base of lactic acid is called lactate (or the lactate anion). 
The name of the derived acyl group is lactoyl.
In solution, Lactic acid can ionize by a loss of a proton to produce the lactate ion CH3CH(OH)CO2–, also known as 2-hydroxypropanoate. 
Compared to acetic acid, Lactic acid's pKa is 1 unit less, meaning that lactic acid is ten times more acidic than acetic acid. 
This higher acidity is the consequence of intramolecular hydrogen bonding between the α-hydroxyl and the carboxylate group.

Lactic acid is chiral, consisting of two enantiomers. 
One is known as Lactic acid, (S)-lactic acid, or (+)-lactic acid, and the other, its mirror image, is D-lactic acid, (R)-lactic acid, or (−)-lactic acid. 
A mixture of the two in equal amounts is called Lactic acid, or racemic lactic acid. 
Lactic acid is hygroscopic. 
Lactic acid is miscible with water and with ethanol above its melting point, which is 16–18 °C (61–64 °F). 
Lactic acid and L-lactic acid have a higher melting point. 
Lactic acid produced by fermentation of milk is often racemic, although certain species of bacteria produce solely D-lactic acid.
On the other hand, lactic acid produced by fermentation in animal muscles has the (L) enantiomer and is sometimes called "sarcolactic" acid, from the Greek sarx, meaning "flesh".

In animals, Lactic acid is constantly produced from pyruvate via the enzyme lactate dehydrogenase (LDH) in a process of fermentation during normal metabolism and exercise.
Lactic acid does not increase in concentration until the rate of lactate production exceeds the rate of lactate removal, which is governed by a number of factors, including monocarboxylate transporters, concentration and isoform of LDH, and oxidative capacity of tissues.
This reaction is reversible and redox-linked: LDH reduces pyruvate to lactate using NADH as an electron donor, simultaneously regenerating NAD⁺ required for glycolysis under anaerobic conditions.
The concentration of blood lactate is usually 1–2 mMTooltip millimolar at rest, but can rise to over 20 mM during intense exertion and as high as 25 mM afterward.
In addition to other biological roles, Lactic acid acid is the primary endogenous agonist of hydroxycarboxylic acid receptor 1 (HCA1), which is a Gi/o-coupled G protein-coupled receptor (GPCR).

In industry, Lactic acid fermentation is performed by lactic acid bacteria, which convert simple carbohydrates such as glucose, sucrose, or galactose to lactic acid. 
These bacteria can also grow in the mouth; the acid they produce is responsible for the tooth decay known as cavities.
In medicine, Lactic acid is one of the main components of lactated Ringer's solution and Hartmann's solution. 
These intravenous fluids consist of sodium and potassium cations along with lactate and chloride anions in solution with distilled water, generally in concentrations isotonic with human blood. 
Lactic acid is most commonly used for fluid resuscitation after blood loss due to trauma, surgery, or burns.
Lactic acid is produced in human tissues when the demand for oxygen is limited by the supply. 
This occurs during tissue ischemia when the flow of blood is limited as in sepsis or hemorrhagic shock. 
Lactic acid may also occur when demand for oxygen is high, such as with intense exercise. 
The process of lactic acidosis produces Lactic acid, which results in an oxygen debt, which can be resolved or repaid when tissue oxygenation improves.
A 2-hydroxy monocarboxylic acid that is propanoic acid in which one of the alpha-hydrogens is replaced by a hydroxy group.

Lactic acid Chemical Properties
Melting point: 18°C
Boiling point: 122 °C/15 mmHg (lit.)
alpha: -0.05 º (c= neat 25 ºC)
density: 1.209 g/mL at 25 °C (lit.)
vapor density: 0.62 (vs air)
vapor pressure: 19 mm of Hg (@ 20°C)
FEMA: 2611 | LACTIC ACID
refractive index: n20/D 1.4262
Fp: >230 °F
storage temp.: 2-8°C
solubility: Miscible with water and with ethanol (96 per cent).
form: syrup
pka: 3.08(at 100℃)
color: Colorless to yellow
Specific Gravity: 1.209
PH: 3.51(1 mM solution);2.96(10 mM solution);2.44(100 mM solution);
Odor: at 100.00 %. odorless
Odor Type: odorless
Water Solubility: SOLUBLE
Merck: 14,5336
JECFA Number: 930
BRN: 1209341
Henry's Law Constant: 1.2×102 mol/(m3Pa) at 25℃, Duchowicz et al. (2020)
Dielectric constant: 22.0（16℃）
Stability: Stable. Combustible. Incompatible with strong oxidizing agents.
Cosmetics Ingredients Functions    SKIN CONDITIONING
HUMECTANT
BUFFERING
Cosmetic Ingredient Review (CIR): Lactic acid (50-21-5)
InChI: 1S/C3H6O3/c1-2(4)3(5)6/h2,4H,1H3,(H,5,6)
InChIKey: JVTAAEKCZFNVCJ-UHFFFAOYSA-N
LogP: -0.72
CAS DataBase Reference: 50-21-5(CAS DataBase Reference)
NIST Chemistry Reference: Propanoic acid, 2-hydroxy-(50-21-5)
EPA Substance Registry System: Lactic acid (50-21-5)

Lactic acid is odorless. 
Lactic acid consists of a mixture of lactic acid (C3H6O3) and lactic acid lactate (C6H10O5). 
The commercial product is the racemic form. 
Lactic acid is usually available in solutions containing 50 to 90% lactic acid.
Lactic acid, CH3CHOHCOOH, also known as 2-hydroxypropanoic acid, is a hygroscopic liquid that exists in three isometric forms. 
Lactic acid is found in blood and animal tissue as a product of glucose and glycogen metabolism. 
Lactic acid is obtained by fermentation of sucrose (corn refining), The racemic mixture is present in foods prepared by bacterial fermentation or prepared synthetically. 
Lactic acid is soluble in water,alcohol,and ether. 
Lactic acid is used as a solvent, in manufacturing confectionery, and in medicine.

Lactic acid consists of a mixture of 2-hydroxypropionic acid, its condensation products, such as lactoyllactic acid and other polylactic acids, and water. 
Lactic acid is usually in the form of the racemate, (RS)-lactic acid, but in some cases the (S)-(+)-isomer is predominant.
A colorless or yellowish, nearly odorless, syrupy liquid consisting of a mixture of lactic acid (C3H6O3) and lactic acid lactate (C6H10O5). 
Lactic acid is obtained by the lactic fermentation of sugars or is prepared synthetically. 
The commercial product is the racemic form. 
Lactic acid is usually available in solutions containing the equivalent of from 50% to 90% lactic acid. 
Lactic acid is hygroscopic, and when concentrated by boiling, the acid condenses to form lactic acid lactate, 2-(lactoyloxy)propanoic acid, which on dilution and heat ing hydrolyzes to lactic acid. 
Lactic acid is miscible with water and with alcohol.

Uses    
Lactic acid is a multi-purpose ingredient used as a preservative, exfoliant, moisturizer, and to provide acidity to a formulation. 
In the body, Lactic acid is found in the blood and muscle tissue as a product of the metabolism of glucose and glycogen. 
Lactic acid is also a component of the skin’s natural moisturizing factor. Lactic acid has better water intake than glycerin. 
Studies indicate an ability to increase the water-retention capacity of the stratum corneum. 
They also show that the pliability of the stratum corneum layer is closely related to the absorption of lactic acid; that is, the greater the amount of absorbed lactic acid, the more pliable the stratum corneum layer. 
Researchers report that continuous use of preparations formulated with lactic acid in concentrations ranging between 5 and 12 percent provided a mild to moderate improvement in fine wrinkling and promote softer, smoother skin. 

Lactic acid's exfoliating properties can help in the process of removing excess pigment from the surface of the skin, as well as improving skin texture and feel. 
Lactic acid is an alpha hydroxy acid occurring in sour milk and other lesser-known sources, such as beer, pickles, and foods made through a process of bacterial fermentation. 
Lactic acid is caustic when applied to the skin in highly concentrated solutions.
Lactic Acid is an acidulant that is a natural organic acid present in milk, meat, and beer, but is normally associated with milk. 
Lactic acid is a syrupy liquid available as 50 and 88% aqueous solutions, and is mis- cible in water and alcohol. 
Lactic acid is heat stable, nonvolatile, and has a smooth, milk acid taste. 
Lactic acid functions as a flavor agent, preservative, and acidity adjuster in foods. 
Lactic acid is used in spanish olives to prevent spoilage and provide flavor, in dry egg powder to improve disper- sion and whipping properties, in cheese spreads, and in salad dress- ing mixes.

Pharmaceutical Applications    
Lactic acid is used in beverages, foods, cosmetics, and pharmaceuticals as an acidifying agent and acidulant.
In topical formulations, particularly cosmetics, Lactic acid 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.
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.

Production Methods    
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 130–200°C 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.