Citric Acid - Wikipedia, The Free Encyclopedia

Names

IUPAC name

2-hydroxypropane-1,2,3-trioic acid

Other names

Citric Acid

3-carboxy-3-hydroxypentanedioic acid

2-hydroxy-1,2,3-propanetricarboxylic acid[1]

Identifiers

CAS RegistryNumber

77-92-9

ATC code A09AB04

ChEBI CHEBI:30769

ChEMBL ChEMBL1261

ChemSpider 305

DrugBank DB04272

EC number 201-069-1

IUPHAR/BPS 2478

Jmol-3D images Image (http://chemapps.stolaf.edu

/jmol/jmol.php?model=OC

%28%3DO%29CC%28O

%29%28C

%28%3DO%29O%29CC

%28%3DO%29O)

KEGG D00037

PubChem 311

RTECS number GE7350000

UNII XF417D3PSL

Properties

Chemical formula C6H8O7

Citric acid

From Wikipedia, the free encyclopedia"E330" redirects here. For the locomotive, see FS Class E330.

Citric acid is a weak organic acid with the formulaC6H8O7. It is a natural preservative which is present incitrus fruits. It is also used to add an acidic or sour taste tofoods and drinks. In biochemistry, the conjugate base ofcitric acid, citrate, is important as an intermediate in thecitric acid cycle, which occurs in the metabolism of allaerobic organisms. It consists of 3 carboxyl (R-COOH)groups.

Citric acid is a commodity chemical, and more than amillion tons are produced every year by fermentation. It isused mainly as an acidifier, as a flavoring, and as achelating agent.

1 Properties2 Discovery and production3 Occurrence4 Biochemistry

4.1 Citric acid cycle4.2 Other biological roles

5 Applications5.1 Foods, other5.2 Cleaning and chelating agent5.3 Cosmetics and pharmaceuticals5.4 Dyeing5.5 Qualitative analysis5.6 Industrial and construction5.7 Photography5.8 Synthesize solid materials from smallmolecules

6 Safety7 Compendial status8 See also9 References10 External links

At room temperature, citric acid is a white hygroscopiccrystalline powder. It can exist either in an anhydrous(water-free) form or as a monohydrate. The anhydrousform crystallizes from hot water, while the monohydrateforms when citric acid is crystallized from cold water. The

InChI

SMILES

Citric acid - Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Citric_acid

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Molar mass 192.12 g·mol−1

Appearance crystalline white solid

Odor odorless

Density 1.665 g/cm3 (anhydrous)

1.542 g/cm3 (18 °C,

monohydrate)

Melting point 156 °C (313 °F; 429 K)

Boiling point 310 °C (590 °F; 583 K)

decomposes from 175 °C[2]

Solubility in water 117.43 g/100 mL (10 °C)

147.76 g/100 mL (20 °C)

180.89 g/100 mL (30 °C)

220.19 g/100 mL (40 °C)

382.48 g/100 mL (80 °C)

547.79 g/100 mL (100 °C)[3]

Solubility soluble in alcohol, ether, ethyl

acetate, DMSO

insoluble in C6H6, CHCl3, CS2,

toluene[2]

Solubility in ethanol 62 g/100 g (25 °C)[2]

Solubility in amyl

acetate4.41 g/100 g (25 °C)[2]

Solubility in diethyl

ether1.05 g/100 g (25 °C)[2]

Solubility in

1,4-Dioxane35.9 g/100 g (25 °C)[2]

log P -1.64

Acidity (pKa) pKa1 = 3.13[4]

pKa2 = 4.76[4]

pKa3 = 6.39,[5] 6.40[6]

Refractive index(nD)

1.493 - 1.509 (20 °C)[3]

1.46 (150 °C)[2]

Viscosity 6.5 cP (50% aq. sol.)[3]

Structure

Crystal structure Monoclinic

Thermochemistry

Specificheat capacity (C)

226.51 J/mol·K (26.85 °C)[7]

Std molar

entropy (So298)

252.1 J/mol·K[7]

Std enthalpy offormation

(ΔfHo

298)

-1548.8 kJ/mol[3]

Citric acid crystal under polarized

light, enlarged 200x

Concentration pH

1M ≈1.57

0.5M ≈1.72

0.1M ≈2.08

Lemons, oranges, limes, and other

citrus fruits possess high

concentrations of citric acid

monohydrate canbe converted tothe anhydrousform by heatingabove 78 °C.Citric acid alsodissolves inabsolute(anhydrous)ethanol (76 partsof citric acid per100 parts ofethanol) at 15 °C.

In chemical structure, citric acidshares the properties of othercarboxylic acids. When heatedabove 175 °C, it decomposesthrough the loss of carbon dioxideand water (see decarboxylation).

Citric acid is a slightly strongeracid than typical carboxylic acids because the anion canbe stabilized by intramolecular hydrogen-bonding fromother protic groups on citric acid.

Medieval scholarsin Europe wereaware of theacidity of lemonand lime juices;such knowledge isrecorded in the13th centuryencyclopediaSpeculum Maius(The GreatMirror), compiledby Vincent ofBeauvais. Citric

acid was first isolated in 1784 by the chemist Carl

Wilhelm Scheele, who crystallized it from lemon juice.[8]

[9]

Industrial-scale citric acid production first began in 1890based on the Italian citrus fruit industry, where the juicewas treated with hydrated lime (calcium hydroxide) toprecipitate calcium citrate, which was isolated and

converted back to the acid using diluted sulfuric acid.[8]

3Ca(OH)2(s) + 2C6H8O7(l) → Ca3(C6H5O7)2(s) +


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Std enthalpy ofcombustion

(ΔcHo298)

-1960.6 kJ/mol[7]

-1972.34 kJ/mol (monohydrate)[3]

Hazards

Main hazards skin and eye irritant

Safety data sheet HMDB (http://www.hmdb.ca

/system/metabolites/msds/000

/000/065/original

/HMDB00094.pdf?1358893891)

GHS pictograms[4]

GHS signal word Warning

GHS hazardstatements

H319[4]

GHS precautionarystatements

P305+351+338[4]

EU classification Xi C

R-phrases R34, R36/37/38, R41

S-phrases S24/25, S26, S36/37/39, S45

NFPA 704

Flash point 155 °C (311 °F; 428 K)

Autoignitiontemperature

345 °C (653 °F; 618 K)

Explosive limits 8%[4]

Lethal dose or concentration (LD, LC):

LD50 (Mediandose)

3000 mg/kg (rats, oral)

Related compounds

Related compounds Sodium citrate

Calcium citrate

Except where otherwise noted, data are given formaterials in their standard state (at 25 °C [77 °F],100 kPa).

verify (what is: / ?)

Infobox references

3H2O(l)

3H2SO4(l) + Ca3(C6H5O7)2(s) → 2C6H8O7(l) +3CaSO4(s)

In 1893, C. Wehmer discovered Penicillium mold couldproduce citric acid from sugar. However, microbialproduction of citric acid did not become industriallyimportant until World War I disrupted Italian citrusexports.In 1917, American food chemist James Currie discoveredcertain strains of the mold Aspergillus niger could beefficient citric acid producers, and the pharmaceuticalcompany Pfizer began industrial-level production usingthis technique two years later, followed by Citrique Belgein 1929.

In this production technique, which is still the majorindustrial route to citric acid used today, cultures of A.niger are fed on a sucrose or glucose-containing mediumto produce citric acid. The source of sugar is corn steepliquor, molasses, hydrolyzed corn starch or other

inexpensive sugary solutions.[10] After the mold is filteredout of the resulting solution, citric acid is isolated byprecipitating it with calcium hydroxide to yield calciumcitrate salt, from which citric acid is regenerated bytreatment with sulfuric acid, as in the direct extractionfrom citrus fruit juice.

In 1977, a patent was granted to Lever Brothers for thechemical synthesis of citric acid starting either fromaconitic or isocitrate/alloisocitrate calcium salts underhigh pressure conditions. This produced citric acid in nearquantitative conversion under what appeared to be a

reverse non-enzymatic Krebs cycle reaction.[11]

In 2007, worldwide annual production stood at

approximately 1,600,000 tons.[12] More than 50% of thisvolume was produced in China. More than 50% was usedas acidity regulator in beverages, some 20% in other foodapplications, 20% for detergent applications and 10% forrelated applications other than food, such as cosmetics,pharmaceutics and in the chemical industry.

Citric acid exists in greater than trace amounts in a varietyof fruits and vegetables, most notably citrus fruits. Lemons and limes have particularly high concentrations

of the acid; it can constitute as much as 8% of the dry weight of these fruits (about 47 g/L in the juices[13]).The concentrations of citric acid in citrus fruits range from 0.005 mol/L for oranges and grapefruits to0.30 mol/L in lemons and limes. Within species, these values vary depending on the cultivar and thecircumstances in which the fruit was grown.


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Citric acid cycle

Main article: Citric acid cycle

Citrate, the conjugate base of citric acid is one of a series of compounds involved in the physiologicaloxidation of acetate from fats, proteins, and carbohydrates. The acetate from these macronutrients areconverted into the intracellular energy of ATP, as well as the common byproducts carbon dioxide, and water.

This series of chemical reactions is central to nearly all metabolic reactions, and is the source of two-thirdsof the food-derived energy in higher organisms. Hans Adolf Krebs received the 1953 Nobel Prize inPhysiology or Medicine for the discovery. The series of reactions is known by various names, including the"citric acid cycle", the "Krebs cycle" or "Szent-Györgyi — Krebs cycle", and the "tricarboxylic acid (TCA)cycle".

Other biological roles

Citrate is a vital component of bone, helping to regulate the size of calcium crystals.[14]

The dominant use of citric acid is as a flavoring and preservative in food and beverages, especially soft

drinks.[8] Within the European Union it is denoted by E number E330. Citrate salts of various metals areused to deliver those minerals in a biologically available form in many dietary supplements. The bufferingproperties of citrates are used to control pH in household cleaners and pharmaceuticals. In the United Statesthe purity requirements for citric acid as a food additive are defined by the Food Chemicals Codex, which ispublished by the United States Pharmacopoeia (USP).

Foods, other

Citric acid can be added to ice cream as an emulsifying agent to keep fats from separating, to caramel toprevent sucrose crystallization, or in recipes in place of fresh lemon juice. Citric acid is used with sodiumbicarbonate in a wide range of effervescent formulae, both for ingestion (e.g., powders and tablets) and forpersonal care (e.g., bath salts, bath bombs, and cleaning of grease). Citric acid is also often used in cleaningproducts and sodas or fizzy drinks.

Citric acid sold in a dry powdered form is commonly sold in markets and groceries as "sour salt", due to itsphysical resemblance to table salt. It has use in culinary applications where an acid is needed for either itschemical properties or for its sour flavor, but a dry ingredient is needed and additional flavors are unwanted(e.g., instead of vinegar or lemon juice).

Cleaning and chelating agent

Citric acid is an excellent chelating agent, binding metals. It is used to remove limescale from boilers and

evaporators.[8] It can be used to soften water, which makes it useful in soaps and laundry detergents. Bychelating the metals in hard water, it lets these cleaners produce foam and work better without need forwater softening. Citric acid is the active ingredient in some bathroom and kitchen cleaning solutions. Asolution with a 6% concentration of citric acid will remove hard water stains from glass without scrubbing. Inthe industry, it is used to dissolve rust from steel. Citric acid can be used in shampoo to wash out wax andcoloring from the hair.


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Illustrative of its chelating abilities, citric acid was the first successful eluant used for total ion-exchangeseparation of the lanthanides, during the Manhattan Project in the 1940s. In the 1950s, it was replaced by thefar more efficient EDTA. It can be used to substantially slow setting of Portland cement.

Cosmetics and pharmaceuticals

Citric acid is widely used as a pH adjusting agent in creams and gels of all kinds. In this role, it is classified inmost jurisdictions as a processing aid and so does not need to be listed on ingredient lists.

Citric acid is an alpha hydroxy acid and used as an active ingredient in chemical peels.

Citric acid is commonly used as a buffer to increase the solubility of brown heroin. Single-use citric acidsachets have been used as an inducement to get heroin users to exchange their dirty needles for clean

needles in an attempt to decrease the spread of HIV and hepatitis.[15] Other acidifiers used for brown heroinare ascorbic acid, acetic acid, and lactic acid; in their absence, a drug user will often substitute lemon juiceor vinegar.

Citric acid is used as one of the active ingredients in the production of antiviral tissues.[16]

Dyeing

Citric acid can be used in food coloring to balance the pH level of a normally basic dye. It is used as anodorless alternative to white vinegar for home dyeing with acid dyes.

Qualitative analysis

Sodium citrate, the sodium salt of citric acid, is used as a chelating agent and is present in the Benedict'sreagent, used for identification both qualitatively and quantitatively, of reducing sugars.

Industrial and construction

Citric acid can be used as a successful alternative to nitric acid in passivation of stainless steel.[17]

Photography

Citric acid can be used as a lower-odor stop bath as part of the process for developing photographic film.Photographic developers are alkaline, so a mild acid is used to neutralize and stop their action quickly, but

commonly used acetic acid leaves a strong vinegar odor in the darkroom.[18]

Synthesize solid materials from small molecules

In materials science, the Citrate-gel method is similar process to sol-gel method which is a method forproducing solid materials from small molecules. During the synthetic process, metal salts or alkoxides areintroduced into a citric acid solution. The formation of citric complexes is believed to balance the differencein individual behaviour of ions in solution, which results in a better distribution of ions and prevents theseparation of components at later process stages. The polycondensation of ethylene glycol and citric acidstarts above 100ºС, resulting in polymer citrate gel formation.

Although a weak acid, exposure to pure citric acid can cause adverse effects: inhalation may cause cough,shortness of breath, or sore throat; ingestion may cause abdominal pain and sore throat; exposure to skin or


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eyes may cause redness or pain.[19] Long-term or repeated consumption may cause erosion of tooth enamel.[19][20][21]

British Pharmacopoeia[22]

Japanese Pharmacopoeia[23]

The closely related acids isocitric acid, aconitic acid, and propane-1,2,3-tricarboxylic acid(tricarballylic acid, carballylic acid)Acids in wine

David R. Lide, ed. (2005). "Physical Constants of Organic Compounds". CRC Handbook of Chemistry andPhysics (http://www.hbcpnetbase.com) (Internet Version ed.). Boca Raton, FL: CRC Press.

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"citric acid" (http://chemister.ru/Database/properties-en.php?dbid=1&id=1624). chemister.ru.2. CID 311 (http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=311) from PubChem3. Sigma-Aldrich Co., Citric acid (http://www.sigmaaldrich.com/catalog/product/sial/251275). Retrieved on2014-06-02.

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Citric acid (http://webbook.nist.gov/cgi/cbook.cgi?ID=C77929&Mask=FFFF&Units=SI) in Linstrom, P.J.;Mallard, W.G. (eds.) NIST Chemistry WebBook, NIST Standard Reference Database Number 69. NationalInstitute of Standards and Technology, Gaithersburg MD. http://webbook.nist.gov (retrieved 2014-06-02)

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Lotfy, Walid A.; Ghanem, Khaled M.; El-Helow, Ehab R. (2007). "Citric acid production by a novel Aspergillusniger isolate: II. Optimization of process parameters through statistical experimental designs". BioresourceTechnology 98 (18): 3470–3477. doi:10.1016/j.biortech.2006.11.032 (https://dx.doi.org/10.1016%2Fj.biortech.2006.11.032). PMID 17317159 (https://www.ncbi.nlm.nih.gov/pubmed/17317159).

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US 4056567-V.Lamberti and E.Gutierrez11. Berovic, M.; Legisa, M. (2007). "Citric acid production". Biotechnology Annual Review Volume 13.Biotechnology Annual Review 13. pp. 303–343. doi:10.1016/S1387-2656(07)13011-8 (https://dx.doi.org/10.1016%2FS1387-2656%2807%2913011-8). ISBN 9780444530325. PMID 17875481(https://www.ncbi.nlm.nih.gov/pubmed/17875481).

12.

Penniston KL, Nakada SY, Holmes RP, Assimos DG; Nakada; Holmes; Assimos (2008). "QuantitativeAssessment of Citric Acid in Lemon Juice, Lime Juice, and Commercially-Available Fruit Juice Products"(http://www.liebertonline.com/doi/pdfplus/10.1089/end.2007.0304) (PDF). Journal of Endourology 22 (3):567–570. doi:10.1089/end.2007.0304 (https://dx.doi.org/10.1089%2Fend.2007.0304). PMC 2637791(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2637791). PMID 18290732 (https://www.ncbi.nlm.nih.gov/pubmed/18290732).

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Wikimedia Commons hasmedia related to Citric acid.

Hu, Y.-Y.; Rawal, A.; Schmidt-Rohr, K. (December 2010). "Strongly bound citrate stabilizes the apatitenanocrystals in bone" (http://www.pnas.org/content/107/52/22425.full). Proceedings of the National Academy ofSciences 107 (52): 22425–22429. Bibcode:2010PNAS..10722425H (http://adsabs.harvard.edu/abs/2010PNAS..10722425H). doi:10.1073/pnas.1009219107 (https://dx.doi.org/10.1073%2Fpnas.1009219107). PMC 3012505 (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3012505).PMID 21127269 (https://www.ncbi.nlm.nih.gov/pubmed/21127269). Retrieved July 28, 2012.

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Garden, J., Roberts, K., Taylor, A., and Robinson, D. (2003). "Evaluation of the Provision of Single Use CitricAcid Sachets to Injecting Drug Users" (pdf) (http://www.drugmisuse.isdscotland.org/eiu/pdfs/citric_acid_full.pdf). Scottish Center for Infection and Environmental Health.

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"Tissues that fight germs" (http://money.cnn.com/2004/07/14/news/fortune500/kleenex/). CNN. July 14, 2004.Retrieved May 8, 2008.

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"Pickling and Passivating Stainless Steel" (http://www.euro-inox.org/pdf/map/Passivating_Pickling_EN.pdf)(PDF). Euro-inox.org. Retrieved 2013-01-01.

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19.

J. Zheng, F. Xiao, L.M. Qian, Z.R. Zhou; Xiao; Qian; Zhou (December 2009). "Erosion behavior of human toothenamel in citric acid solution". Tribology International 42 (11–12): 1558–1564.doi:10.1016/j.triboint.2008.12.008 (https://dx.doi.org/10.1016%2Fj.triboint.2008.12.008).

20.

"Effect of Citric Acid on Tooth Enamel" (http://www.livestrong.com/article/147503-the-effect-of-citric-acid-on-tooth-enamel).

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British Pharmacopoeia Commission Secretariat (2009). "Index, BP 2009" (http://www.pharmacopoeia.co.uk/pdf/2009_index.pdf) (PDF). Retrieved February 4, 2010.

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"Japanese Pharmacopoeia, Fifteenth Edition" (http://jpdb.nihs.go.jp/jp15e/JP15.pdf) (PDF). 2006. Retrieved4 February 2010.

23.

Citric acid MS Spectrum (http://gmd.mpimp-golm.mpg.de/Spectrums/8ae1d7de-7822-4e4c-9729-8cdab8862c44.aspx)The European Citric Acid Manufacturers Association(http://www.ecama.org)NextBio Citric Acid Entry (http://www.nextbio.com/b/home/home.nb?q=Citric+acid)Citric acid analysis – free spreadsheet for titration of acids and pH calculation (http://www2.iq.usp.br/docente/gutz/Curtipot_.html)Applications of Citric Acid (http://www.kasel.at/kasel-chemicals/products-applications/products/citric-acid-2013-applications-key-industrial-uses)National Institutes of Health Household Products Database (http://householdproducts.nlm.nih.gov/cgi-bin/household/brands?tbl=chem&id=13&query=citric+acid&searchas=TblChemicals)

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Citric Acid - Wikipedia, The Free Encyclopedia