Citric acid also dissolves in absolute (anhydrous) ethanol (76 parts of citric acid per 100 parts of ethanol) at 15 ☌. The monohydrate can be converted to the anhydrous form at about 78 ☌. The anhydrous form crystallizes from hot water, while the monohydrate forms when citric acid is crystallized from cold water. Chemical characteristics Speciation diagram for a 10-millimolar solution of citric acidĬitric acid can be obtained as an anhydrous (water-free) form or as a monohydrate. More than 50% was used as an acidity regulator in beverages, some 20% in other food applications, 20% for detergent applications, and 10% for applications other than food, such as cosmetics, pharmaceuticals, and in the chemical industry. More than 50% of this volume was produced in China. Global production was in excess of 2,000,000 tons in 2018. In 1977, a patent was granted to Lever Brothers for the chemical synthesis of citric acid starting either from aconitic or isocitrate (also called alloisocitrate) calcium salts under high pressure conditions this produced citric acid in near quantitative conversion under what appeared to be a reverse, non-enzymatic Krebs cycle reaction. After the mold is filtered out of the resulting suspension, citric acid is isolated by precipitating it with calcium hydroxide to yield calcium citrate salt, from which citric acid is regenerated by treatment with sulfuric acid, as in the direct extraction from citrus fruit juice. The source of sugar is corn steep liquor, molasses, hydrolyzed corn starch, or other inexpensive, carbohydrate solution. In this production technique, which is still the major industrial route to citric acid used today, cultures of A. niger are fed on a sucrose or glucose-containing medium to produce citric acid. In 1917, American food chemist James Currie discovered that certain strains of the mold Aspergillus niger could be efficient citric acid producers, and the pharmaceutical company Pfizer began industrial-level production using this technique two years later, followed by Citrique Belge in 1929. However, microbial production of citric acid did not become industrially important until World War I disrupted Italian citrus exports. Wehmer discovered Penicillium mold could produce citric acid from sugar. Industrial-scale citric acid production first began in 1890 based on the Italian citrus fruit industry, where the juice was treated with hydrated lime ( calcium hydroxide) to precipitate calcium citrate, which was isolated and converted back to the acid using diluted sulfuric acid. The concentrations of citric acid in citrus fruits range from 0.005 mol/L for oranges and grapefruits to 0.30 mol/L in lemons and limes these values vary within species depending upon the cultivar and the circumstances under which the fruit was grown.Ĭitric acid was first isolated in 1784 by the chemist Carl Wilhelm Scheele, who crystallized it from lemon juice. Lemons and limes have particularly high concentrations of the acid it can constitute as much as 8% of the dry weight of these fruits (about 47 g/L in the juices ). Natural occurrence and industrial production Lemons, oranges, limes, and other citrus fruits contain high concentrations of citric acid.Ĭitric acid occurs in a variety of fruits and vegetables, most notably citrus fruits. When part of a salt, the formula of the citrate anion is written as C An example of the former, a salt is trisodium citrate an ester is triethyl citrate. Ī citrate is a derivative of citric acid that is, the salts, esters, and the polyatomic anion found in solution. It is used widely as an acidifier, as a flavoring, and a chelating agent. More than two million tons of citric acid are manufactured every year. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in the metabolism of all aerobic organisms. The factor-label method yields the desired cancellation of units, and the computed result is on the order of 10 22 as expected.Citric acid is an organic compound with the chemical formula HOC(CO 2H)(CH 2CO 2H) 2.
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