Term: Citric acid

**Natural Occurrence and Industrial Production**:
– Citric acid is naturally found in high concentrations in lemons, oranges, limes, and other citrus fruits.
– It was first isolated in 1784 by Carl Wilhelm Scheele from lemon juice.
– Industrial-scale production started in 1890 using Italian citrus fruit treated with hydrated lime.
– Concentrations vary within species and cultivars.

**Chemical Characteristics and Biochemistry**:
– Citric acid can be obtained in anhydrous or monohydrate forms and acts as a tribasic acid with specific pK values.
– It plays a crucial role in the citric acid cycle as an intermediate.
– The citric acid cycle is a central metabolic pathway for animals, plants, and bacteria.
– Citrate synthase catalyzes the formation of citrate in the cycle.

**Industrial Applications and Health Impact**:
– Over two million tons of citric acid are produced annually.
– China contributes over 50% of the global volume.
– Citric acid is widely used in beverages, food, detergents, cosmetics, pharmaceuticals, and the chemical industry.
– It is generally recognized as safe for consumption but can be corrosive in high concentrations.

**Applications in Various Industries**:
– Citric acid is extensively used as a flavoring and preservative in food and beverages.
– It is a common ingredient in ice cream, caramel, and effervescent formulas.
– Citric acid is utilized in cleaning products as a chelating agent and in bathroom and kitchen cleaning solutions.
– It is also found in cosmetics, pharmaceuticals, dietary supplements, and as a passivation treatment for stainless steel.

**Research, Studies, and Safety**:
– Studies focus on citric acid quantification in fruit juices, its role in biological systems, and its applications in various fields.
– Citric acid is researched for its effects on urine composition and calcium stone formation.
– Safety aspects include erosion behavior on tooth enamel and guidelines from organizations like NIOSH and pharmacopoeial standards.

Citric acid (Wikipedia)

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Citric acid is an organic compound with the chemical formula HOC(CO₂H)(CH₂CO₂H)₂. It is a colorless weak organic acid. 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.

Citric acid

Names
IUPAC name Citric acid
Preferred IUPAC name 2-Hydroxypropane-1,2,3-tricarboxylic acid
Identifiers
CAS Number	77-92-9 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:30769 Y
ChEMBL	ChEMBL1261 Y
ChemSpider	305 Y
DrugBank	DB04272 Y
ECHA InfoCard	100.000.973
EC Number	201-069-1
E number	E330 (antioxidants, ...)
IUPHAR/BPS	2478
KEGG	D00037 Y
PubChem CID	311 22230 (monohydrate)
RTECS number	GE7350000
UNII	XF417D3PSL Y
CompTox Dashboard (EPA)	DTXSID3020332
InChI InChI=1S/C6H8O7/c7-3(8)1-6(13,5(11)12)2-4(9)10/h13H,1-2H2,(H,7,8)(H,9,10)(H,11,12) Y Key: KRKNYBCHXYNGOX-UHFFFAOYSA-N Y InChI=1/C6H8O7/c7-3(8)1-6(13,5(11)12)2-4(9)10/h13H,1-2H2,(H,7,8)(H,9,10)(H,11,12) Key: KRKNYBCHXYNGOX-UHFFFAOYAM
SMILES OC(=O)CC(O)(C(=O)O)CC(=O)O
Properties
Chemical formula	C6H8O7
Molar mass	192.123 g/mol (anhydrous), 210.14 g/mol (monohydrate)
Appearance	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
Solubility in water	54% w/w (10 °C) 59.2% w/w (20 °C) 64.3% w/w (30 °C) 68.6% w/w (40 °C) 70.9% w/w (50 °C) 73.5% w/w (60 °C) 76.2% w/w (70 °C) 78.8% w/w (80 °C) 81.4% w/w (90 °C) 84% w/w (100 °C)
Solubility	Soluble in acetone, alcohol, ether, ethyl acetate, DMSO Insoluble in C 6H 6, 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 pKa4 = 14.4
Refractive index (nD)	1.493–1.509 (20 °C) 1.46 (150 °C)
Viscosity	6.5 cP (50% aq. sol.)
Structure
Crystal structure	Monoclinic
Thermochemistry
Heat capacity (C)	226.51 J/(mol·K) (26.85 °C)
Std molar entropy (S⦵298)	252.1 J/(mol·K)
Std enthalpy of formation (ΔfH⦵298)	−1543.8 kJ/mol
Heat of combustion, higher value (HHV)	1985.3 kJ/mol (474.5 kcal/mol, 2.47 kcal/g), 1960.6 kJ/mol 1972.34 kJ/mol (471.4 kcal/mol, 2.24 kcal/g) (monohydrate)
Pharmacology
ATC code	A09AB04 (WHO)
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Skin and eye irritant
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H290, H319, H315
Precautionary statements	P305+P351+P338
NFPA 704 (fire diamond)	2 1 0
Flash point	155 °C (311 °F; 428 K)
Autoignition temperature	345 °C (653 °F; 618 K)
Explosive limits	8%
Lethal dose or concentration (LD, LC):
LD50 (median dose)	3000 mg/kg (rats, oral)
Safety data sheet (SDS)	HMDB
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

More than two million tons of citric acid are manufactured every year. It is used widely as an acidifier, as a flavoring, and a 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 anion is written as C
₆H
₅O³⁻
₇ or C
₃H
₅O(COO)³⁻
₃.

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