Citric Acid
Natural and Biologically Compatible: Citric acid naturally occurs in plants and animals and plays a key role in cellular respiration, making it highly biocompatible and suitable for food, pharmaceutical, and biological applications.
Multi-Functional Chemical Reactivity: With three carboxyl groups, citric acid can release hydrogen ions stepwise and form citrate ions, enabling effective pH regulation and versatile chemical interactions in various formulations.
Excellent Metal Chelation Ability: Citric acid readily combines with metal ions to form stable citrate salts, such as calcium citrate, which is widely used in food fortification, medicine, and industrial applications.
Strong Derivative and Ester Formation Capability: It can form a variety of citrate esters (e.g., trimethyl citrate, triethyl citrate), expanding its use in plasticizers, pharmaceuticals, cosmetics, and specialty chemicals.
Citric acid is a white, crystalline, mildly acidic organic compound that occurs naturally in most plants and many animals, where it functions as an intermediate in cellular respiration. Because it contains three carboxyl groups, it is classified as a carboxylic acid, more specifically a tricarboxylic acid. The term “citrus” comes from the Greek word kedromelon, meaning “apple of melon,” referring to the citron fruit. Ancient Greek writings mention kitron, kitrion, or kitreos to describe the citron, an oblong fruit several inches long produced by the shrub-like tree Citrus medica. Lemons and limes are particularly rich in citric acid, which can account for up to 8% of their dry weight.
As a weak acid, citric acid releases hydrogen ions from its three carboxyl (COOH) groups when dissolved in solution. When one hydrogen ion is lost from each group, the citrate ion (C₃H₅O(COO)₃³⁻) is formed. During partial ionization, intermediate ions may also be generated. The citrate ion readily binds with metal ions to form salts, the most common example being calcium citrate. In addition, citric acid can react to form esters, producing various citrate compounds such as trimethyl citrate and triethyl citrate.
Citric acid is widely used as an acidulant and antioxidant and is typically produced through mold fermentation of sugar solutions, as well as by extraction from lemon juice, lime juice, and pineapple processing residues. It is the primary acid found in oranges, lemons, and limes and is available in both anhydrous and monohydrate forms. The anhydrous form crystallizes from hot solutions, while the monohydrate form crystallizes from cooler solutions below 36.5 °C. At 20 °C, the solubility of anhydrous citric acid is about 146 g/100 mL of distilled water, whereas citric acid monohydrate dissolves at approximately 175 g/100 mL. A 1% aqueous solution has a pH of around 2.3 at 25 °C.
Citric acid Chemical Properties
Melting point | 153-159 °C (lit.) |
Boiling point | 248.08°C (rough estimate) |
density | 1.67 g/cm3 at 20 °C |
vapor density | 7.26 (vs air) |
vapor pressure | <0.1 hPa (20 °C) |
refractive index | 1.493~1.509 |
FEMA | 2306 | CITRIC ACID |
Fp | 100 °C |
storage temp. | 2-8°C |
solubility | Citric acid also dissolves in absolute (anhydrous) ethanol (76 parts of citric acid per 100 parts of ethanol) at 15 °C. |
form | grit |
pka | 3.14(at 20℃) |
color | White |
PH | 3.24(1 mM solution);2.62(10 mM solution);2.08(100 mM solution); |
Odor | Odorless |
Odor Type | odorless |
explosive limit | 8%, 65°F |
Water Solubility | soluble in Water (1174g/L at 10°C, 1809g/L at 30°C, 3825g/L at 80°C). |
Sensitive | Hygroscopic |
λmax | λ: 260 nm Amax: 0.20 |
Merck | 14,2326 |
JECFA Number | 218 |
BRN | 782061 |
Stability: | Stable. Incompatible with bases, strong oxidizing agents, reducing agents, metal nitrates. |
InChIKey | KRKNYBCHXYNGOX-UHFFFAOYSA-N |
LogP | -1.64 |
CAS DataBase Reference | 77-92-9(CAS DataBase Reference) |
NIST Chemistry Reference | 1,2,3-Propanetricarboxylic acid, 2-hydroxy-(77-92-9) |
EPA Substance Registry System | Citric acid (77-92-9) |
Safety Information
Hazard Codes | Xi,C,T |
Risk Statements | 41-36/37/38-36/38-37/38-34-36-35-61-60 |
Safety Statements | 26-39-37/39-24/25-36/37/39-45-36-53 |
RIDADR | UN 1789 8/PG 3 |
WGK Germany | 1 |
RTECS | GE7350000 |
F | 9 |
TSCA | Yes |
HS Code | 2918 14 00 |
Hazardous Substances Data | 77-92-9(Hazardous Substances Data) |
Toxicity | LD50 in mice, rats (mmol/kg): 5.0, 4.6 i.p. (Gruber, Halbeisen) |
With its hygroscopic nature and strong, tart taste, citric acid is extensively used in the food industry. Typical applications include fruit drinks and carbonated beverages at levels of 0.25–0.40%, cheese at 3–4%, and jellies. It also serves as an antioxidant in products such as instant potatoes, wheat chips, and potato sticks, where it helps prevent spoilage by chelating metal ions. Furthermore, when used alongside other antioxidants, it helps inhibit discoloration in fresh frozen fruits.
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