2326. Citric Acid

Nomenclature

CAS number: 77-92-9
2-Hydroxy-1,2,3-propanetricarboxylic acid; β-hydroxytricarballylic acid.
C6H8O7; mol wt 192.12.
C 37.51%, H 4.20%, O 58.29%.

Description and references

Widely distributed in plants and in animal tissues and fluids. Produced by mycological fermentation on an industrial scale using crude sugar solns, such as molasses and strains of Aspergillus niger: See review by Von Loesecke, Chem. Eng. News 23, 1952 (1945); Schweiger, US 2970084 (1961 to Miles Labs.); Faith, Keyes & Clark's Industrial Chemicals, F. A. Lowenheim, M. K. Moran, Eds. (Wiley-Interscience, New York, 4th ed., 1975) pp 275-279. Also extracted from citrus fruits (lemon juice contains 5 to 8%) and from pineapple waste. Reviews: Wilson, Chem. Metall. Eng. 29, 787 (1923); Browne, Ind. Eng. Chem. 13, 81 (1921); Warneford, Hardy, ibid. 17, 1283 (1925); E. F. Bouchard, E. G. Merritt in Kirk-Othmer Encyclopedia of Chemical Technology vol. 6 (Wiley-Interscience, New York, 3rd ed., 1979) pp 150-179. Toxicity: C. M. Gruber, Jr., W. A. Halbeisen, J. Pharmacol. Exp. Ther. 94, 65 (1948).

Chemical structure

Properties

Anhydr form, mp 153°. Crystals are monoclinic holohedra and crystallize from hot concd aq soln. d 1.665. At 25°, pK1 3.128; pK2 4.761; pK3 6.396, Bates, Pinching, J. Am. Chem. Soc. 71, 1274 (1949). Soly in water: 54.0% w/w at 10°; 59.2% at 20°; 64.3% at 30°; 68.6% at 40°; 70.9% at 50°; 73.5% at 60°; 76.2% at 70°; 78.8% at 80°; 81.4% at 90°; 84.0% at 100°. LD50 in mice, rats (mmol/kg): 5.0, 4.6 i.p. (Gruber, Halbeisen).

Derivative

Monohydrate.

Nomenclature

CAS number: 5949-29-1
C6H8O7.H2O; mol wt 210.14.
C 34.29%, H 4.80%, O 60.91%.

Properties

Orthorhombic crystals from cold aq solns. Pleasant, sour taste. d 1.542. Monohydrate crystals lose water of crystn in dry air or when heated at about 40 to 50°, slightly deliquescent in moist air. Softens at 75°. mp ≈100°. pH of 0.1N soln = 2.2. Densities of aqueous soln (15°/15°): 10% = 1.0392; 20% = 1.0805; 30% = 1.1244; 40% = 1.1709; 50% = 1.2204; 60% = 1.2738. Soly in g/100 g satd soln: ether 2.17; chloroform 0.007; amyl alcohol 15.43; amyl acetate 5.98; ethyl acetate 5.28. Soly at 19° in g/100 g solvent: methanol 197; propanol 62.8.

Derivative

Barium salt heptahydrate.

Nomenclature

CAS number: 6487-29-2
Barium citrate.
C12H10Ba3O14.7H2O; mol wt 916.29.
C 15.73%, H 2.64%, Ba 44.96%, O 36.67%.

Properties

Powder. Loses all H2O at 150°. Sol in 1750 parts water; freely sol in dil HCl or HNO3; practically insol in alcohol.

Derivative

Ethyl ester.

Nomenclature

CAS number: 77-93-0
Ethyl citrate; triethyl citrate.
C12H20O7; mol wt 276.28.
C 52.17%, H 7.30%, O 40.54%.

Properties

Bitter, oily liq. d20 1.137. bp760 294°; bp1.0 127°. Viscosity at 25°: 35.2 cP. Pour pt ≈10°. nD20 1.4455. Soly: water ≈6.9%; peanut oil 0.8%. Misc with alc, ether.

Derivative

Disodium salt.

Nomenclature

CAS number: 144-33-2
Disodium hydrogen citrate; sodium acid citrate; Alkacitron (PDH).
C6H6Na2O7; mol wt 236.09.
C 30.52%, H 2.56%, Na 19.48%, O 47.44%.

Properties

White powder, saline taste. One gram of sesquihydrate dissolves in slightly less than 2 ml water; pH of a 3% w/v soln in water: 4.9 to 5.2. LD50 in mice, rats (mmol/kg): 7.5, 7.3 i.p. (Gruber, Halbeisen).

Derivative

Trisodium salt.

Description and references

See Sodium Citrate.

Use

Anticoagulant, generally in solution with glucose, to prevent the clotting of blood intended for transfusion. Acidulant in beverages, confectionery, effervescent salts, in pharmaceutical syrups, elixirs, in effervescent powders and tablets, to adjust the pH of foods and as synergistic antioxidant, in processing cheese. Used in beverages, jellies, jams, preserves and candy to provide tartness. In the manuf of alkyd resins; in esterified form as plasticizer, foam inhibitor. In the manuf of citric acid salts. As sequestering agent to remove trace metals. As mordant to brighten colors; in electroplating; in special inks; in analytical chemistry for determining citrate-soluble P2O5; as reagent for albumin, mucin, glucose, bile pigments.