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Lactic acid

Lactic acid
Names
Preferred IUPAC name
2-Hydroxypropanoic acid[1]
Other names
  • Lactic acid[1]
  • Milk acid
Identifiers
3D model (JSmol)
3DMet
1720251
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.000.017 Edit this at Wikidata
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
Miscible[2]
Acidity (pKa) 3.86,[3] 15.1[4]
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[5]
H315, H318[5]
P280, P305+P351+P338[5]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Lactic acid is an organic acid. It has the molecular formula C3H6O3. It is white in the solid state and it is miscible with water.[2] When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as well as 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 used as 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, it can ionize by a loss of a proton to produce the lactate ion CH
3CH(OH)CO−
2. Compared to acetic acid, its pKa is 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.

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. Lactic acid is hygroscopic. DL-Lactic acid is miscible with water and with ethanol above its melting point, which is about 16 to 18 °C (61 to 64 °F). D-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.[6] On the other hand, lactic acid produced by anaerobic respiration in animal muscles has the (L) enantiomer and is sometimes called "sarcolactic" acid, from the Greek sarx, meaning "flesh".

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.[7] 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.[7] 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.[8][9] In addition to other biological roles, L-lactic acid is the primary endogenous agonist of hydroxycarboxylic acid receptor 1 (HCA1), which is a Gi/o-coupled G protein-coupled receptor (GPCR).[10][11]

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.[12][13][14][15] 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.

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. It 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.[16]

  1. ^ a b "CHAPTER P-6. Applications to Specific Classes of Compounds". Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 748. doi:10.1039/9781849733069-00648. ISBN 978-0-85404-182-4.
  2. ^ a b Record in the GESTIS Substance Database of the Institute for Occupational Safety and Health
  3. ^ Dawson RM, et al. (1959). Data for Biochemical Research. Oxford: Clarendon Press.
  4. ^ Silva AM, Kong X, Hider RC (October 2009). "Determination of the pKa value of the hydroxyl group in the alpha-hydroxycarboxylates citrate, malate and lactate by 13C NMR: implications for metal coordination in biological systems". Biometals. 22 (5): 771–8. doi:10.1007/s10534-009-9224-5. PMID 19288211. S2CID 11615864.
  5. ^ a b c Sigma-Aldrich Co., DL-Lactic acid.
  6. ^ "(S)-lactic acid (CHEBI:422)". www.ebi.ac.uk. Retrieved 5 January 2024.
  7. ^ a b Summermatter S, Santos G, Pérez-Schindler J, Handschin C (May 2013). "Skeletal muscle PGC-1α controls whole-body lactate homeostasis through estrogen-related receptor α-dependent activation of LDH B and repression of LDH A". Proceedings of the National Academy of Sciences of the United States of America. 110 (21): 8738–43. Bibcode:2013PNAS..110.8738S. doi:10.1073/pnas.1212976110. PMC 3666691. PMID 23650363.
  8. ^ "Lactate Profile". UC Davis Health System, Sports Medicine and Sports Performance. Retrieved 23 November 2015.
  9. ^ Goodwin ML, Harris JE, Hernández A, Gladden LB (July 2007). "Blood lactate measurements and analysis during exercise: a guide for clinicians". Journal of Diabetes Science and Technology. 1 (4): 558–69. doi:10.1177/193229680700100414. PMC 2769631. PMID 19885119.
  10. ^ Offermanns S, Colletti SL, Lovenberg TW, Semple G, Wise A, IJzerman AP (June 2011). "International Union of Basic and Clinical Pharmacology. LXXXII: Nomenclature and Classification of Hydroxy-carboxylic Acid Receptors (GPR81, GPR109A, and GPR109B)". Pharmacological Reviews. 63 (2): 269–90. doi:10.1124/pr.110.003301. PMID 21454438.
  11. ^ Offermanns S, Colletti SL, IJzerman AP, Lovenberg TW, Semple G, Wise A, Waters MG. "Hydroxycarboxylic acid receptors". IUPHAR/BPS Guide to Pharmacology. International Union of Basic and Clinical Pharmacology. Retrieved 13 July 2018.
  12. ^ Badet C, Thebaud NB (2008). "Ecology of lactobacilli in the oral cavity: a review of literature". The Open Microbiology Journal. 2: 38–48. doi:10.2174/1874285800802010038. PMC 2593047. PMID 19088910.
  13. ^ Nascimento MM, Gordan VV, Garvan CW, Browngardt CM, Burne RA (April 2009). "Correlations of oral bacterial arginine and urea catabolism with caries experience". Oral Microbiology and Immunology. 24 (2): 89–95. doi:10.1111/j.1399-302X.2008.00477.x. PMC 2742966. PMID 19239634.
  14. ^ Aas JA, Griffen AL, Dardis SR, Lee AM, Olsen I, Dewhirst FE, Leys EJ, Paster BJ (April 2008). "Bacteria of dental caries in primary and permanent teeth in children and young adults". Journal of Clinical Microbiology. 46 (4): 1407–17. doi:10.1128/JCM.01410-07. PMC 2292933. PMID 18216213.
  15. ^ Caufield PW, Li Y, Dasanayake A, Saxena D (2007). "Diversity of lactobacilli in the oral cavities of young women with dental caries". Caries Research. 41 (1): 2–8. doi:10.1159/000096099. PMC 2646165. PMID 17167253.
  16. ^ Achanti, Anand; Szerlip, Harold M. (1 January 2023). "Acid-Base Disorders in the Critically Ill Patient". Clin J Am Soc Nephrol. 18 (1): 102–112. doi:10.2215/CJN.04500422. ISSN 1555-9041. PMC 10101555. PMID 35998977.

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