Lactic acid

Lactic acid
L-lactic acid skeletal formula
D-lactic acid skeletal formula
L-lactic acid ball and stick model
D-lactic acid ball and stick model
Names
Preferred IUPAC name
2-hydroxypropanoic acid
Other names
  • lactic acid
  • milk acid
Identifiers
  • 50-21-5 checkY
  • 79-33-4 (L) checkY
  • 10326-41-7 (D) checkY
3D model (JSmol)
1720251
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.000.017
EC Number
  • 200-018-0
E number E270 (preservatives)
362717
KEGG
RTECS number
  • OD2800000
UNII
UN number 3265
  • InChI=1S/C3H6O3/c1-2(4)3(5)6/h2,4H,1H3,(H,5,6)/t2-/m0/s1 checkY
    Key: JVTAAEKCZFNVCJ-REOHCLBHSA-N checkY
  • CC(O)C(=O)O
Properties
C3H6O3
Molar mass 90.078 g·mol−1
Melting point 18 °C (64 °F; 291 K)
Boiling point 122 °C (252 °F; 395 K) at 15 mmHg
86.1% w/w at 20°C
88.6% w/w at 25°C
Acidity (pKa) 3.86, 15.1
Thermochemistry
1361.9 kJ/mol, 325.5 kcal/mol, 15.1 kJ/g, 3.61 kcal/g
Related compounds
Other anions
 lactate
Related compounds
Pharmacology
G01AD01 (WHO) QP53AG02 (WHO)
Hazards
GHS labelling:
GHS05: Corrosive
H315, H318
P280, P305+P351+P338
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Lactic acid is an organic acid with the molecular formula C3H6O3. In its solid state, it is white and in its liquid state is miscible with water. When dissolved, it forms a colorless solution. Production includes both artificial synthesis and natural sources. Lactic acid is an alpha-hydroxy acid (AHA) due to the presence of a hydroxyl group adjacent to the carboxyl group. It 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.

Lactic acid is chiral, consisting of two enantiomers. One is known as L-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 DL-lactic acid, or racemic lactic acid.

In animals, L-lactate is constantly produced from pyruvate via the enzyme lactate dehydrogenase (LDH) in a process of fermentation during normal metabolism and exercise. It 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. Lactic acid is produced in human tissues when the demand for oxygen is limited by the supply. The process of lactic acidosis produces lactic acid, which results in an oxygen debt, which can be resolved or repaid when tissue oxygenation improves.

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 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, lactate 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. It is most commonly used for fluid resuscitation after blood loss due to trauma, surgery, or burns.

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