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Citric acid

Citric acid is a weak organic acid that has 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 C6H5O3−7 or C3H5O(COO)3−3.

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Further Information

Names

Preferred IUPAC name: 2-Hydroxypropane-1,2,3-tricarboxylic acid

Other names

Citric acid

Identifiers

CAS Number: 77-92-9

JSmol: Interactive image

ChEBI: CHEBI:30769

ChEMBL: ChEMBL1261

ChemSpider: 305

DrugBank: DB04272

ECHA InfoCard: 100.000.973

EC Number: 201-069-1

E number: (antioxidants, …)

IUPHAR/BPS: 2478

KEGG: D00037

PubChem: 311

RTECS number: GE7350000

UNII: XF417D3PSL

Properties

Chemical formula: C6H8O7

Molar mass: 192.12 g·mol

Appearance: crystalline white solid

Odor: odorless

Density: 1.665 g/cm (anhydrous)
1.542 g/cm (18 °C, monohydrate)33

Melting point: 156 °C (313 °F; 429 K)

Boiling point: 310 °C (590 °F; 583 K) decomposes from 175 °C

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)

Solubility: alcohol

Solubility: 62 g/100 g (25 °C)

Solubility: 4.41 g/100 g (25 °C)

Solubility: 1.05 g/100 g (25 °C)

Solubility: 35.9 g/100 g (25 °C)

log : −1.64

K: K

Refractive index: 1.493–1.509 (20 °C)
1.46 (150 °C)

Viscosity: 6.5 cP (50% aq. sol.)

Structure

Crystal structure: Monoclinic

Thermochemistry

Specific
heat capacity: 226.51 J/(mol·K) (26.85 °C)

Std molar
entropy: 252.1 J/(mol·K)

Std enthalpy of
formation: −1548.8 kJ/mol

Std enthalpy of
combustion: −1960.6 kJ/mol
−1972.34 kJ/mol (monohydrate)

Pharmacology

ATC code: WHOA09AB04

Hazards

hazards: skin and eye irritant

Safety data sheet: HMDB

GHS pictograms:

GHS signal word: Warning

GHS hazard statements: H319

GHS precautionary statements: P305+351+338

NFPA 704:

Flash point: 155 °C (311 °F; 428 K)

Autoignition
temperature: 345 °C (653 °F; 618 K)

Explosive limits: 8%

median dose: 3000 mg/kg (rats, oral)

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

Infobox references