Citric Acid Anhydrate CAS: 77-92-9
Citric Acid Monohydrate CAS: 5949-29-1
Citric acid (beta-hydroxytricarboxylic acid or 2-hydroxy-1,2,3-propane tricarboxylic acid) occurs widely
in both plants and animals. The compound is produced by fermentation and used primarily in the
food/beverage industry, where its high solubility, tart flavor, acidity and buffering capabilities make it the
world¡¯s most widely adapted acidulant/preservative. Citric acid is a natural occuring fruit acid, produced
commercially by microbial fermentation of a carbohydrate substrate.
Citric acid¡¯s one hydroxy and three carboxyl groups permit the formation of a wide variety of complex
molecules. The chemical characteristic that makes it a valuable industrial chemical is its ability to
complex with metal ions, most notably the alkaline earths calcium and magnesium and also the transition
metals copper, nickel, zinc and cobalt. It is an excellent chelating agent and a very good sequestering
agent. In many end-use markets, the presence of even trace amounts of metal ions can adversely affect the
color, stability, clarity or overall appearance of the final product or negatively affect the efficiency of a
process. Citric acid does not chelate sodium or potassium, but rather forms their salts.
Citric Acid also called 2-hydroxy-1,2,3-propanetricarboxylic acid, HO2CCH2C(OH)(CO2H)CH2CO2H, an organic carboxylic acid containing three carboxyl groups ; it is a solid at room temperature, melts at 153¡ãC, and decomposes at higher temperatures. It is responsible for the tart taste of various fruits in which it occurs, e.g., lemons, limes, oranges, pineapples, and gooseberries. It can be extracted from the juice of citrus fruits by adding calcium oxide (lime) to form calcium citrate, an insoluble precipitate that can be collected by filtration; the citric acid can be recovered from its calcium salt by adding sulfuric acid. It is obtained also by fermentation of glucose with the aid of the mold Aspergillus niger and can be obtained synthetically from acetone or glycerol. Citric acid is used in soft drinks and in laxatives and cathartics. Its salts, the citrates, have many uses, e.g., ferric ammonium citrate is used in making blueprint paper. Sour salt, used in cooking, is citric acid.
The discovery of citric acid has been credited to the 8th century Arab-Yemeni (Iranian-born) alchemist Jabir Ibn Hayyan (Geber). Medieval scholars in Europe were aware of the acidic nature of lemon and lime juices; such knowledge is recorded in the 13th century encyclopedia Speculum Majus (The Great Mirror), compiled by Vincent of Beauvais. Citric acid was first isolated in 1784 by the Swedish chemist Carl Wilhelm Scheele, who crystallized it from lemon juice. Industrial-scale citric acid production began in 1860, based on the Italian citrus fruit industry.
In 1893, C. Wehmer discovered that Penicillium mold could produce citric acid from sugar. However, microbial production of citric acid did not become industrially important until World War I disrupted Italian citrus exports. In 1917, the American food chemist James Currie discovered that certain strains of the mold Aspergillus niger could be efficient citric acid producers, and Pfizer began industrial-level production using this technique two years later.
Citric acid was originally obtained by the physical extraction of the acid from lemon juice. Worldwide,
most commercial production of citric acid is now accomplished by fermentation processes using either
dextrose or beet molasses as raw material and Aspergillus niger mold as the fermenting organism.
Fermentation can be carried out in deep tanks (submerged fermentation being the most commonly
preferred) or shallow pans (surface fermentation). Shallow-pan fermentation is preferred in some
instances because of relatively lower energy costs; however, it also requires more square footage and
regular agitation. A number of noncarbohydrate-based citric acid routes have been patented, but none is
known to be in commercial operation. Some citric acid ¡°producers¡± throughout the world only convert
crude citric acid (unrefined calcium citrate) into refined citric acid.
In the deep tank process, air is forced into the medium, causing fermentation to occur. The fermentation
cycle runs five to fourteen days. The submerged culture process has been the preferred process, especially
in large-volume production in the industrial world, because it requires less labor and is easier to maintain
aseptically in industrial operations. Disadvantages of this process include (1) the need for higher power
input and (2) stringent control of the purity of the sugar solution, which is critical to the citric acid yield.
Citric acid yield from submerged culture fermentation processes can be from 80% to 95%, based on the
weight of the sugar. Actual yields obtained throughout the world depend on the purity of the carbohydrate
raw material and the efficiency of the organism.
In the surface pan process, air circulates over a layer of the medium, allowing fermentation to occur
primarily on the surface. The fermentation cycle is reported to run six to eleven days. This process is not
currently used in the United States, but variations of the surface culture process still account for a
reasonable portion of citric acid production, particularly in agriculturally rich, less industrialized nations.
Recovery and purification of citric acid are similar for both the surface and the submerged culture
fermentation routes. After fermentation, citric acid is commercially separated from the liquor by one of
two possible methods:
1. Precipitation as calcium citrate tetrahydrate
2. Liquid extraction
Most citric acid is used as a flavoring and preservative in food and beverages, especially soft drinks; it is denoted by E Number E330. Citrate salts of various metals are used to deliver those minerals in a biologically available form in many dietary supplements. The buffering properties of citrates are used to control pH in household cleaners and pharmaceuticals.
Citric acid's ability to chelate metals gives it use in soaps and laundry detergents. By chelating the metals in hard water, it lets these cleaners produce foam and work better without need for water softening. Similarly, citric acid is used to regenerate the ion exchange materials used in water softeners by stripping off the accumulated metal ions as citrate complexes.
It is used in the biotechnology and pharmaceutical industry to passivate high purity process piping in lieu of using nitric acid, since nitric is a hazardous disposal issue once it is used for this purpose, while citric is not.
In the United Kingdom, pharmacies control the sale of Citric acid. Citric acid is a popular buffer used to increase the solubility of street heroin in Scotland. Single-use citric acid sachets have been used as an inducement to get heroin users to exchange their dirty needles for clean needles in an attempt to decrease the spread of AIDS and hepatitis. See the .pdf article here (http://www.drugmisuse.isdscotland.org/eiu/pdfs/citric_acid_full.pdf). Other acidifiers used for brown heroin are ascorbic acid, acetic acid, and lactic acid: in their absence, the drug abuser will often substitute lemon juice or vinegar.
Citric acid is recognized as safe for use in food by all major national and international food regulatory agencies. It is naturally present in almost all forms of life, and excess citric acid is readily metabolized and eliminated from the body.
Contact with dry citric acid or with concentrated solutions can result in skin and eye irritation, so protective clothing should be worn when handling these materials
Chemical Name: C6H8O7 , or alternatively:CH2(COOH).COH(COOH).CH 2 (COOH)
Formula Weight: 192.13
Melting point: 153¡æ
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