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Citrate

Citric acid
Zitronensäure - Citric acid.svg
Citric-acid-3D-balls.png
Names
Preferred IUPAC name
2-Hydroxypropane-1,2,3-tricarboxylic acid
Other names
Citric acid
Identifiers
77-92-9 YesY
3D model (Jmol) Interactive image
ChEBI CHEBI:30769 YesY
ChEMBL ChEMBL1261 YesY
ChemSpider 305 YesY
DrugBank DB04272 YesY
ECHA InfoCard 100.000.973
EC Number 201-069-1
E number E330 (antioxidants, ...)
2478
KEGG D00037 YesY
PubChem 22230 (monohydrate) 311, 22230 (monohydrate)
RTECS number GE7350000
UNII XF417D3PSL YesY
Properties
C6H8O7
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
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)
Solubility soluble in alcohol, ether, ethyl acetate, DMSO
insoluble in C6H6, CHCl3, CS2, toluene
Solubility in ethanol 62 g/100 g (25 °C)
Solubility in amyl acetate 4.41 g/100 g (25 °C)
Solubility in diethyl ether 1.05 g/100 g (25 °C)
Solubility in 1,4-Dioxane 35.9 g/100 g (25 °C)
log P −1.64
Acidity (pKa) pKa1 = 3.13
pKa2 = 4.76
pKa3 = 6.39, 6.40
1.493–1.509 (20 °C)
1.46 (150 °C)
Viscosity 6.5 cP (50% aq. sol.)
Structure
Monoclinic
Thermochemistry
226.51 J/(mol·K) (26.85 °C)
252.1 J/(mol·K)
−1548.8 kJ/mol
−1960.6 kJ/mol
−1972.34 kJ/mol (monohydrate)
Pharmacology
A09AB04 (WHO)
Hazards
Main hazards skin and eye irritant
Safety data sheet HMDB
GHS pictograms The exclamation-mark pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word Warning
H319
P305+351+338
Irritant Xi Corrosive C
R-phrases R34, R36/37/38, R41
S-phrases S24/25, S26, S36/37/39, S45
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point 155 °C (311 °F; 428 K)
345 °C (653 °F; 618 K)
Explosive limits 8%
Lethal dose or concentration (LD, LC):
LD50 (median dose)
3000 mg/kg (rats, oral)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YesYN ?)
Infobox references

Citric acid is a weak organic tricarboxylic acid having the chemical formula C6H8O7. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in the metabolism of all aerobic organisms.

More than a million tons of citric acid are manufactured every year. It is used widely as an acidifier, as a flavoring and chelating agent.

A citrate is a derivative of citric acid; that is, the salts, esters, and the polyatomic anion found in solution. An example of the former, a salt is trisodium citrate; an ester is triethyl citrate. When part of a salt, the formula of the citrate ion is written as C6H5O73− or C3H5O(COO)33−.

Citric acid exists in greater than trace amounts in a variety of 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). The concentrations of citric acid in citrus fruits range from 0.005 mol/L for oranges and grapefruits to 0.30 mol/L in lemons and limes. Within species, these values vary depending on the cultivar and the circumstances in which the fruit was grown.

Industrial-scale citric acid production first began in 1890 based on the Italian citrus fruit industry, where the juice was treated with hydrated lime (calcium hydroxide) to precipitate calcium citrate, which was isolated and converted back to the acid using diluted sulfuric acid. In 1893, C. Wehmer discovered Penicillium mold could produce citric acid from sugar. However, microbial production of citric acid did not become industrially important until World War I disrupted Italian citrus exports.


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