Editing Lactic acid (section)

{{Short description|Organic acid}}
{{Use dmy dates|date=July 2018}}
{{chembox
|Verifiedfields = 
|Watchedfields = changed
|verifiedrevid = 477002503
|Name = Lactic acid
|ImageFileL1 = Lactic-acid-skeletal.svg
|ImageSizeL1 = 130
|ImageFileR1 = Lactic-acid-from-xtal-3D-bs-17.png
|ImageSizeR1 = 130
|ImageCaption2 = {{sc|L}}-Lactic acid
|PIN = 2-Hydroxypropanoic acid<ref name=iupac2013>{{cite book | title =  Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book) | publisher = [[Royal Society of Chemistry|The Royal Society of Chemistry]] | date = 2014 | location = Cambridge | page = 748 | doi = 10.1039/9781849733069-00648 | isbn = 978-0-85404-182-4| chapter = CHAPTER P-6. Applications to Specific Classes of Compounds }}</ref>
|OtherNames = {{ubl|Lactic acid<ref name=iupac2013 />|Milk acid}}
|Section1 = {{Chembox Identifiers
|IUPHAR_ligand = 2932
|3DMet = B01180
|Beilstein = 1720251
|CASNo_Ref = {{cascite|correct|CAS}}
|CASNo = 50-21-5
|CASNo1_Ref = {{cascite|correct|CAS}}
|CASNo1 = 79-33-4
|CASNo1_Comment = ({{sc|L}})
|CASNo2_Ref = {{cascite|correct|CAS}}
|CASNo2 = 10326-41-7
|CASNo2_Comment = ({{sc|D}})
|ChEMBL_Ref = {{ebicite|correct|EBI}}
|ChEMBL = 330546
|EC_number = 200-018-0
|UNII_Ref = {{fdacite|correct|FDA}}
|UNII = 3B8D35Y7S4
|UNII1_Ref = {{fdacite|correct|FDA}}
|UNII1 = F9S9FFU82N
|UNII1_Comment = ({{sc|L}})
|UNII2_Ref = {{fdacite|correct|FDA}}
|UNII2 = 3Q6M5SET7W
|UNII2_Comment = ({{sc|D}})
|ChEBI_Ref = {{ebicite|correct|EBI}}
|ChEBI = 422
|KEGG = D00111
|KEGG1 = C00186
|KEGG2 = C00256
|Gmelin = 362717
|RTECS = OD2800000
|UNNumber = 3265
|PubChem = 612
|StdInChI_Ref = {{stdinchicite|correct|chemspider}}
|StdInChI = 1S/C3H6O3/c1-2(4)3(5)6/h2,4H,1H3,(H,5,6)/t2-/m0/s1
|StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
|StdInChIKey = JVTAAEKCZFNVCJ-REOHCLBHSA-N
|ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
|ChemSpiderID = 96860
|SMILES = CC(O)C(=O)O
}}
|Section2 = {{Chembox Properties
|C=3 | H=6 | O=3
|Solubility=Miscible<ref name=GESTIS>{{GESTIS|ZVG=13000}}</ref>
|MeltingPtC =18
|BoilingPtC = 122
|BoilingPt_notes = at 15{{nbsp}}mmHg
|pKa = 3.86,<ref>{{cite book| vauthors = Dawson RM |display-authors=etal|title=Data for Biochemical Research|location=Oxford|publisher=Clarendon Press|date=1959}}</ref> 15.1<ref>{{cite journal | vauthors = Silva AM, Kong X, Hider RC |title = 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 | journal = Biometals | volume = 22 | issue = 5 | pages = 771–8 | date = October 2009 | pmid = 19288211 | doi = 10.1007/s10534-009-9224-5 | s2cid = 11615864 }}</ref>
}}
|Section3 = {{Chembox Thermochemistry| DeltaHc = 1361.9{{nbsp}}kJ/mol, 325.5{{nbsp}}kcal/mol, 15.1{{nbsp}}kJ/g, 3.61{{nbsp}}kcal/g}}
|Section4 = {{Chembox Related
|OtherAnions = Lactate
|OtherFunction_label = [[carboxylic acid]]s
|OtherFunction = {{ubl|[[Acetic acid]]|[[Glycolic acid]]|[[Propionic acid]]|[[3-Hydroxypropanoic acid]]|[[Malonic acid]]|[[Butyric acid]]|[[Hydroxybutyric acid]]}}
|OtherCompounds = {{ubl|[[1-Propanol]]|[[2-Propanol]]|[[Propionaldehyde]]|[[Acrolein]]|[[Sodium lactate]]|[[Ethyl lactate]]}}
}}
|Section5 = {{Chembox Pharmacology
|ATCCode_prefix = G01
|ATCCode_suffix = AD01
|ATC_Supplemental = {{ATCvet|P53|AG02}}
}}
|Section6 = {{Chembox Hazards
|GHSPictograms = {{GHS05}}<ref name="sigma">{{Sigma-Aldrich|sial|id=69785|name={{small|DL}}-Lactic acid|access-date=20 July 2013}}</ref>
|HPhrases = {{H-phrases|315|318}}<ref name="sigma" />
|PPhrases = {{P-phrases|280|305+351+338}}<ref name="sigma" />
}}
}}

'''Lactic acid''' is an [[organic acid]]. It has the molecular formula '''C<sub>3</sub>H<sub>6</sub>O<sub>3</sub>'''. It is white in the solid state and it is [[miscibility|miscible]] with water.<ref name=GESTIS/> 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]] {{chem|CH|3|CH(OH)CO|2|−}}. Compared to [[acetic acid]], its [[Acid dissociation constant|p''K''{{sub|a}}]] 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 [[chirality (chemistry)|chiral]], consisting of two [[enantiomer]]s. One is known as {{sc|L}}-lactic acid, (''S'')-lactic acid, or (+)-lactic acid, and the other, its mirror image, is {{sc|D}}-lactic acid, (''R'')-lactic acid, or (−)-lactic acid. A mixture of the two in equal amounts is called {{sc|DL}}-lactic acid, or [[racemic]] lactic acid. Lactic acid is [[hygroscopy|hygroscopic]]. {{sc|DL}}-Lactic acid is [[miscible]] with water and with ethanol above its melting point, which is about {{cvt|16 to 18|C}}. {{sc|D}}-Lactic acid and {{sc|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 {{sc|D}}-lactic acid.<ref>{{Cite web |title=(S)-lactic acid (CHEBI:422) |url=https://www.ebi.ac.uk/chebi/searchId.do?printerFriendlyView=true&locale=null&chebiId=422&viewTermLineage=null&structureView=& |access-date=2024-01-05 |website=www.ebi.ac.uk}}</ref> On the other hand, lactic acid produced by fermentation in animal muscles has the ({{sc|L}}) enantiomer and is sometimes called "sarcolactic" acid, from the Greek {{transliteration|grc|sarx}}, meaning "flesh".

In animals, {{sc|L}}-lactate is constantly produced from [[pyruvate]] via the [[enzyme]] [[lactate dehydrogenase]] (LDH) in a process of [[fermentation (biochemistry)|fermentation]] during normal [[metabolism]] and [[exercise]].<ref name="Skeletal muscle PGC-1α controls who">{{cite journal | vauthors = Summermatter S, Santos G, Pérez-Schindler J, Handschin C | title = Skeletal muscle PGC-1α controls whole-body lactate homeostasis through estrogen-related receptor α-dependent activation of LDH B and repression of LDH A | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 110 | issue = 21 | pages = 8738–43 | date = May 2013 | pmid = 23650363 | pmc = 3666691 | doi = 10.1073/pnas.1212976110 | bibcode = 2013PNAS..110.8738S | doi-access = free }}</ref> 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 transporter]]s, concentration and isoform of LDH, and oxidative capacity of tissues.<ref name="Skeletal muscle PGC-1α controls who"/> The concentration of [[blood]] lactate is usually {{nowrap|1–2}}{{nbsp}}{{abbrlink|mM|millimolar}} at rest, but can rise to over 20{{nbsp}}mM during intense exertion and as high as 25{{nbsp}}mM afterward.<ref name="LA-UCD">{{cite web | url=http://www.ucdmc.ucdavis.edu/sportsmedicine/resources/lactate_description.html | title=Lactate Profile | publisher=UC Davis Health System, Sports Medicine and Sports Performance | access-date=23 November 2015}}</ref><ref>{{cite journal | vauthors = Goodwin ML, Harris JE, Hernández A, Gladden LB | title = Blood lactate measurements and analysis during exercise: a guide for clinicians | journal = Journal of Diabetes Science and Technology | volume = 1 | issue = 4 | pages = 558–69 | date = July 2007 | pmid = 19885119 | pmc = 2769631 | doi = 10.1177/193229680700100414 }}</ref> In addition to other biological roles, {{sc|L}}-lactic acid is the primary [[endogenous]] [[agonist]] of [[hydroxycarboxylic acid receptor 1]] (HCA{{sub|1}}), which is a {{nowrap|[[Gi alpha subunit|G{{sub|i/o}}-coupled]]}} [[G protein-coupled receptor]] (GPCR).<ref name="IUPHAR's comprehensive 2011 review on HCARs">{{cite journal | vauthors = Offermanns S, Colletti SL, Lovenberg TW, Semple G, Wise A, IJzerman AP | title = International Union of Basic and Clinical Pharmacology. LXXXII: Nomenclature and Classification of Hydroxy-carboxylic Acid Receptors (GPR81, GPR109A, and GPR109B) | journal = Pharmacological Reviews | volume = 63 | issue = 2 | pages = 269–90 | date = June 2011 | pmid = 21454438 | doi = 10.1124/pr.110.003301 | doi-access = free }}</ref><ref name="IUPHAR-DB HCAR family page">{{cite web | vauthors = Offermanns S, Colletti SL, IJzerman AP, Lovenberg TW, Semple G, Wise A, Waters MG |title=Hydroxycarboxylic acid receptors |url=http://www.guidetopharmacology.org/GRAC/FamilyDisplayForward?familyId=48 |website=IUPHAR/BPS Guide to Pharmacology |publisher=International Union of Basic and Clinical Pharmacology |access-date=13 July 2018}}</ref>

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 [[Tooth decay|cavities]].<ref>{{cite journal | vauthors = Badet C, Thebaud NB | title = Ecology of lactobacilli in the oral cavity: a review of literature | journal = The Open Microbiology Journal | volume = 2 | pages = 38–48 | year = 2008 | pmid = 19088910 | pmc = 2593047 | doi =  10.2174/1874285800802010038  |doi-access=free}}</ref><ref>{{cite journal | vauthors = Nascimento MM, Gordan VV, Garvan CW, Browngardt CM, Burne RA | title = Correlations of oral bacterial arginine and urea catabolism with caries experience | journal = Oral Microbiology and Immunology | volume = 24 | issue = 2 | pages = 89–95 | date = April 2009 | pmid = 19239634 | pmc = 2742966 | doi = 10.1111/j.1399-302X.2008.00477.x }}</ref><ref>{{cite journal | vauthors = Aas JA, Griffen AL, Dardis SR, Lee AM, Olsen I, Dewhirst FE, Leys EJ, Paster BJ | title = Bacteria of dental caries in primary and permanent teeth in children and young adults | journal = Journal of Clinical Microbiology | volume = 46 | issue = 4 | pages = 1407–17 | date = April 2008 | pmid = 18216213 | pmc = 2292933 | doi = 10.1128/JCM.01410-07 }}</ref><ref>{{cite journal | vauthors = Caufield PW, Li Y, Dasanayake A, Saxena D | title = Diversity of lactobacilli in the oral cavities of young women with dental caries | journal = Caries Research | volume = 41 | issue = 1 | pages = 2–8 | year = 2007 | pmid = 17167253 | pmc = 2646165 | doi = 10.1159/000096099 }}</ref> 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]] [[cation]]s along with lactate and [[chloride]] [[anion]]s in solution with distilled [[water]], generally in concentrations [[isotonicity|isotonic]] with [[human]] [[blood]]. It is most commonly used for fluid [[resuscitation]] after blood loss due to [[physical trauma|trauma]], [[surgery]], or [[burn (injury)|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 [[wikt:oxygen debt|oxygen debt]] which can be resolved or repaid when tissue oxygenation improves.<ref>{{Cite journal |last1=Achanti |first1=Anand |last2=Szerlip |first2=Harold M. |date=1 January 2023 |title=Acid-Base Disorders in the Critically Ill Patient |journal=Clin J Am Soc Nephrol |language=en |volume=18 |issue=1 |pages=102–112 |doi=10.2215/CJN.04500422 |issn=1555-9041 |pmc=10101555 |pmid=35998977}}</ref>