Lactic acid

Lactic acid

L-Lactic acid
rac-Lactic acid
Names
Preferred IUPAC name 2-Hydroxypropanoic acid
Other names Lactic acid Milk acid
Identifiers
CAS Number	50-21-5 Y 79-33-4 (L) Y 10326-41-7 (D) Y
3D model (Jmol)	Interactive image
ChEBI	CHEBI:422 Y
ChEMBL	ChEMBL330546 Y
ChemSpider	96860 Y
ECHA InfoCard	100.000.017
E number	E270 (preservatives)
IUPHAR/BPS	2932
UNII	33X04XA5AT N
InChI InChI=1S/C3H6O3/c1-2(4)3(5)6/h2,4H,1H3,(H,5,6)/t2-/m0/s1 Y Key: JVTAAEKCZFNVCJ-REOHCLBHSA-N Y
SMILES CC(O)C(=O)O
Properties
Chemical formula	C3H6O3
Molar mass	90.07948
Melting point	L: 53 °C D: 53 °C D/L: 16.8 °C
Boiling point	122 °C (252 °F; 395 K) @ 12 mmHg
Acidity (pKa)	3.86, 15.1
Thermochemistry
Std enthalpy of combustion (ΔcHo298)	1361.9 kJ/mol, 325.5 kcal/mol, 15.1 kJ/g, 3.61 kcal/g
Pharmacology
ATC code	G01AD01 (WHO) QP53AG02 (WHO)
Hazards
GHS pictograms
GHS hazard statements	H315, H318
GHS precautionary statements	P280, P305+351+338
Related compounds
Other anions	lactate
Related carboxylic acids	acetic acid glycolic acid propionic acid 3-hydroxypropanoic acid malonic acid butyric acid hydroxybutyric acid
Related compounds	1-propanol 2-propanol propionaldehyde acrolein sodium lactate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

Lactic acid is an organic compound with the formula CH₃CH(OH)CO₂H. In its solid state, it is white and water-soluble. In its liquid state, it is clear. It is produced both naturally and synthetically. With a hydroxyl group adjacent to the carboxyl group, lactic acid is classified as an alpha-hydroxy acid (AHA). In the form of its conjugate base called lactate, it plays a role in several biochemical processes.

In solution, it can ionize a proton from the carboxyl group, producing the lactate ion CH
3CH(OH)CO−
2. Compared to acetic acid, its pK_a is 1 unit less, meaning lactic acid deprotonates ten times more easily than acetic acid does. This higher acidity is the consequence of the intramolecular hydrogen bonding between the α-hydroxyl and the carboxylate group.

Lactic acid is chiral, consisting of two optical isomers. One is known as L-(+)-lactic acid or (S)-lactic acid and the other, its mirror image, is D-(−)-lactic acid or (R)-lactic acid. A mixture of the two in equal amounts is called DL-lactic acid, or racemic lactic acid.

Lactic acid is hygroscopic. DL-lactic acid is miscible with water and with ethanol above its melting point which is around 17 or 18 °C. D-lactic acid and L-lactic acid have a higher melting point.

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. The concentration of blood lactate is usually 1–2 mmol/L at rest, but can rise to over 20 mmol/L during intense exertion and as high as 25 mmol/L afterward.