Term: Citric acid

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**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)

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
Stereo skeletal formula of citric acid
Stereo skeletal formula of citric acid
Ball-and-stick model of citric acid
Ball-and-stick model of citric acid
Crystal sample from the saturated citric acid solution.
IUPAC name
Citric acid
Preferred IUPAC name
2-Hydroxypropane-1,2,3-tricarboxylic acid
3D model (JSmol)
ECHA InfoCard 100.000.973 Edit this at Wikidata
EC Number
  • 201-069-1
E number E330 (antioxidants, ...)
RTECS number
  • GE7350000
  • 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) checkY
  • 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)
  • OC(=O)CC(O)(C(=O)O)CC(=O)O
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
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
, 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
1.493–1.509 (20 °C)
1.46 (150 °C)
Viscosity 6.5 cP (50% aq. sol.)
226.51 J/(mol·K) (26.85 °C)
252.1 J/(mol·K)
−1543.8 kJ/mol
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)
A09AB04 (WHO)
Occupational safety and health (OHS/OSH):
Main hazards
Skin and eye irritant
GHS labelling:
GHS05: CorrosiveGHS07: Exclamation mark
H290, H319, H315
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformFlammability 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
Flash point 155 °C (311 °F; 428 K)
345 °C (653 °F; 618 K)
Explosive limits 8%
Lethal dose or concentration (LD, LC):
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).
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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
or C

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