Lactic acid

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Lactic acid
Names
IUPAC name
2-Hydroxypropanoic acid
Other names
Milk acid
Properties
C3H6O3
CH3CH(OH)COOH
Molar mass 90.078 g/mol
Appearance Colorless liquid or solid
Odor Faint, milk-like
Density 1.206 g/cm3 (20 °C)
Melting point 16.8 °C (62.2 °F; 289.9 K)
Boiling point 122 °C (252 °F; 395 K) (at 15 mm Hg)
Solubility Soluble in diethyl ether, ethanol, furfural, glycerol, methanol, propylene glycol
Insoluble in benzene, carbon disulfide, chloroform, petroleum ether
Vapor pressure 0.0813 mmHg at 25 °C
Acidity (pKa) 3.83
Thermochemistry
Hazards
Safety data sheet Sigma-Aldrich (DL)
Sigma-Aldrich (L-(+))
Sigma-Aldrich (D-(-))
Flash point 110 °C (235 °F; 383 K)
Related compounds
Related compounds
Glycolic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Lactic acid is an organic acid with the formula CH3CH(OH)COOH. Lactic acid is an alpha-hydroxy acid (AHA) due to the presence of carboxyl group adjacent to the hydroxyl group.

Lactic acid is chiral, consisting of two enantiomers. 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.

Properties

Chemical

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

Physical

Lactic acid is a colorless solid or liquid, extremely soluble in water. Its solubility is so high that 1 part of lactic acid can dissolve 12 parts of water. It has a faint milk-like odor, often described as acrid.

Availability

Lactic acid is sold by many food and cosmetic suppliers, most often than not as 80% or 60% aq. solution.

Solid lactic acid is sold by chemical suppliers, though the solution form is more readily available.

Preparation

Lactic acid is produced industrially by bacterial fermentation of glucose, lactose or sucrose.

Reduction of pyruvic acid will yield racemic lactic acid.

Projects

  • Make pyruvic acid
  • Make copper lactate
  • Make polylactic acid

Handling

Safety

Lactic acid has low toxicity.

Storage

In closed bottles.

Disposal

No special disposal is required. Can be poured down the drain.

References

Relevant Sciencemadness threads