Citric acidGeneralPropertiesStructureHazardsSupplementary data pageRelated compounds
Systematic name2-hydroxypropane- 1,2,3-tricarboxylic acid
Other names?
Empirical formulaC6H8O7
Molar mass192.027 g/mol
Appearancecrystalline white solid
CAS number<77-92-9>
Density and phase1.665 g/cm³
Solubility in water133 g/100 ml (20°C)
Melting point153 °C (307.4 °F, 426 K)
Boiling pointdecomposes in ~ 175 °C (448 K)
Acidity (pKa)pKa1=3.15pKa2=4.77pKa3=6.40
Viscosity? cP at ?°C
Crystal structure?
Dipole moment? D
Main hazardsskin and eye irritant
NFPA 704


Flash point?°C
R/S statementR: ? S: ?
RTECS number?
Structure andpropertiesn, εr, etc.

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ThermodynamicdataPhase behaviourSolid, liquid, gas
Spectral dataUV, IR, NMR, MS
Related compoundssodium citrate, calcium citrate
Except where detailed otherwise, data are given for products in their standard state (at 25°C, 100 kPa)Infobox disclaimer and references

Citric acid is a weak organic acid discovered in citrus fruits, which room fruits that flowering plants of the genus Citrus in the household Rutaceae, originating in tropical and subtropical southeast Asia, and including lemon, grapefruit, orange, tangerine, and lime. In biochemistry, citric acid is essential as an intermediate in the citric mountain cycle and also therefore wake up in the metabolism of nearly all life things.

Citric acid shows both the great and poor use of person creativity. Manufacturing techniques have actually been developed for its uses as a food additive—citric acid is a organic preservative and also is also used to add an acidic (sour) taste to foods and soft drinks—;as one environmentally benign clean agent; as an antioxidant (slows or avoids the oxidation of various other chemicals); to store fat globules different in ice cream; amongst many uses. ~ above the various other hand, citric acid is required to develop HMTD, one explosive with problem in regards to terrorism, and also as a buffer to rise the solubility that brown heroin in the illegal drug industry.

Worldwide, about one million lots of citric acid space commercially created each year (Soccol et al., 2003).

Citric mountain exists in a range of fruits and vegetables, however it is most focused in lemons and limes, where it can consist of as lot as eight percent of the dry weight of the fruit.



At room temperature, citric mountain is a white crystalline powder. It have the right to exist one of two people in one anhydrous (water-free) form, or together a monohydrate that has one water molecule because that every molecule of citric acid. The anhydrous kind crystallizes from warm water, if the monohydrate develops when citric mountain is crystallized indigenous cold water. The monohydrate deserve to be converted to the anhydrous type by heater it over 74°C.

Citric acid additionally dissolves in absolute (anhydrous) ethanol (76 parts of citric acid per 100 components of ethanol) at 15°C.

Chemically, citric acid shares the nature of various other carboxylic acids. (organic acids defined by the presence of a carboxyl group, which has the formula -C(=O)OH, normally written -COOH or -CO2H.) once heated over 175 \°C, that decomposes v the loss of carbon dioxide and water.

History that Discovery

The discovery of citric acid has actually been credited to the eighth-century alchemist Jabir Ibn Hayyan (also known as Geber), who also discovered hydrochloric mountain (from salt), nitric mountain (from saltpeter), acetic acid (from vinegar), and tartaric mountain (from wine-making residues).


Medieval scholars in Europe were mindful of the acidic nature the lemon and also lime juices; such expertise is taped in the thirteenth-century encyclopedia Speculum Majus (The good Mirror), compiled by Vincent of Beauvais.

Citric mountain was an initial isolated in 1784 by the swedish chemist Carl Wilhelm Scheele, that crystallized that from lemon juice.


Industrial-scale citric acid production started in 1860, based upon the Italian citrus fruit industry.

In 1893, C. Wehmer uncovered that Penicillium mold might produce citric acid from sugar. However, microbial production of citric acid did not become industrially important until people War i disrupted Italian citrus exports. In 1917, the American food chemist James Currie discovered that details strains the the mold Aspergillus niger might be efficient citric mountain producers, and also Pfizer began industrial-level production using this an approach two years later.

In this manufacturing technique, i m sorry is tho the significant industrial path to citric acid provided today, cultures of Aspergillus niger are fed top top sucrose to create citric acid. After ~ the mold is filtered out of the resulting solution, citric acid is isolated by precipitating it with lime (calcium hydroxide) to yield calcium citrate salt, native which citric acid is regenerated through treatment through sulfuric acid.

Alternatively, citric mountain is sometimes isolated indigenous the fermentation broth by liquid-liquid extraction with a hydrocarbon equipment of the organic basic trilaurylamine, adhered to by re-extraction from the organic systems by water.

Annual production of citric acid is around one million tons, do citric acid among the fermentation commodities with the highest levels the production an international (Soccol et al., 2003). Around 70% the the full citric acid production is spend by the food industry (Prado et al. 2005).

Citric mountain Cycle

Main article: citric mountain cycle

Citric acid is among a series of compounds connected in metabolic pathway that forms part of the breakdown of carbohydrates, fats, and also proteins right into carbon dioxide and also water in order to create energy. This is the citric mountain cycle (also known as the tricarboxylic acid cycle and also as the Krebs cycle).

The citric mountain cycle is a series of chemical reactions of main importance in all living cells that make use of oxygen to generate helpful energy by cellular respiration. Essentially, the cycle entails converting the potential power of a range of nutrients into the readily obtainable energy that adenosine triphosphate (ATP). This bicycle is the "power plant" the energizes all metabolism.

Citrate is one intermediary in the citric mountain cycle. A citrate is an ionic kind of citric acid, such as C3H5O(COO)33−, the is, citric acid minus three hydrogen ions.

The citric mountain cycle the resource of two-thirds that the food-derived power in higher organisms.


As a food additive, citric mountain is supplied as a flavoring and also preservative in food and also beverages, particularly soft drinks. The is denoted through E number E330. (E numbers are codes because that food additives provided on food brand in the europe Union and some nations outside this region.) Citrate salts of various steels are offered to supply those mineral in a biologically available type in many dietary supplements. The buffering properties of citrates are provided to control pH in family members cleaners and also pharmaceuticals.

Citric acid"s capability to chelate metals (reversible binding the a ligant to a metal ion) renders it beneficial in soaps and laundry detergents. By chelating the metals in tough water, it lets these cleaners create foam and work better without require for water softening. Similarly, citric acid is supplied to regenerate the ion exchange materials used in water softeners through stripping turn off the accumulated metal ions as citrate complexes.

Citric mountain is the active ingredient in part bathroom and also kitchen cleaning solutions. A systems with a six percent concentration that citric acid will remove difficult water stains from glass there is no scrubbing.

Citric acid is provided in the biotechnology and pharmaceutical industry to passivate (make product passive or non-reactive) high purity procedure piping (in lieu of making use of nitric acid). Nitric mountain is taken into consideration hazardous to dispose once provided for this purpose, while citric mountain is not.

Citric acid deserve to be added to ice cream cream to store fat globules separate and also can be added to recipes in place of new lemon juice as well. Citric acid is used along with sodium bicarbonate in a wide variety of effervescent formulas, both for ingestion (e.g., powders and also tablets) and for personal care (e.g., bathtub salts, bathtub beads, and cleaning that grease).

When used to hair, citric acid opens up the external layer, additionally known together the cuticle. While the cuticle is open, it enables for a depths penetration into the hair shaft. It have the right to be supplied in shampoo come wash out wax and coloring indigenous the hair. That is especially used in the product "Sun-in" for bleaching, but is usually not recommended due to the amount of damage it causes.

Citric mountain is also used as a avoid bath in photography. The developer is generally alkaline, therefore a mild acid will certainly neutralize it, boosting the effectiveness of the protect against bath when contrasted to plain water.

Citric acid is one of the chemicals forced for the synthesis of hexamethylene triperoxide diamine (HMTD), a highly heat-, friction-, and shock-sensitive explosive comparable to acetone peroxide. To buy of big quantities that citric acid might rouse uncertainty of potential terror activity.


Citric mountain is well-known as safe for usage in food by all significant national and international food regulation agencies. It is naturally present in practically all develops of life, and also excess citric mountain is easily metabolized and eliminated from the body.

Interestingly, in spite of its ubiquity, intolerance come citric acid in the diet is well-known to exist. Little information is accessible as the condition shows up to be rare, yet like other species of food intolerance the is often explained as a "pseudo-allergic" reaction.

Contact v dry citric acid or with focused solutions can an outcome in skin and also eye irritation, for this reason protective garments should be worn when dealing with these materials.

There have been erroneous reports that E330 is a major cause the cancer. It is believed that this has been brought around by misunderstanding and also confusion over the word Krebs. In this case, it refers to Sir Hans Adolf Krebs, discoverer the the Krebs cycle, and also not the German word for cancer. Citric acid is not recognized to be harmful to the body once taken alone.

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