Calcium citrate

Calcium citrate

Calcium citrate tetrahydrate[1]
IUPAC name
2-hydroxy-1,2,3-propane-tricarboxylic acid calcium salt (2:3)
Other names
E333, tricalcium dicitrate
813-94-5 N
5785-44-4 (tetrahydrate) N
3D model (Jmol) Interactive image
ChemSpider 12584 YesY
EC Number 212-391-7
E number E333 (antioxidants, ...)
PubChem 13136
Molar mass 498.4334 g/mol (anhydrous)
570.4945 g/mol (tetrahydrate)
Appearance White powder
Odor odorless
Density 1.63 g/cm3 (anhydrous)
2.00 g/cm3 (tetrahydrate)[1]
Melting point Decomposes
Boiling point Decomposes
0.85 g/L (18 °C)
0.95 g/L (25 °C)
Solubility insoluble in alcohol
Triclinic (tetrahydrate)
P1, No. 2
a = 0.59466(4) nm, b = 1.02247(8) nm, c = 1.66496(13) nm
α = 72.213(7)°, β = 79.718(7)°, γ = 89.791(6)°[1]
Main hazards Irritant
Safety data sheet External MSDS
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Related compounds
Other cations
Sodium citrate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox references

Calcium citrate is the calcium salt of citric acid. It is commonly used as a food additive (E333), usually as a preservative, but sometimes for flavor. In this sense, it is similar to sodium citrate. Calcium citrate is also found in some dietary calcium supplements (e.g. Citracal). Calcium makes up 24.1% of calcium citrate (anhydrous) and 21.1% of calcium citrate (tetrahydrate) by mass. The tetrahydrate occurs in nature as the mineral Earlandite.

Chemical properties

Calcium citrate is sparingly soluble in water. Needle-shaped crystals of tricalcium dicitrate tetrahydrate [Ca3(C6H5O7)2(H2O)2]·2H2O were obtained by hydrothermal synthesis. The crystal structure comprises a three-dimensional network in which eightfold coordinated Ca2+ cations are linked by citrate anions and hydrogen bonds between two non-coordinating crystal water molecules and two coordinating water molecules.[1]


Calcium citrate is an intermediate in the isolation of citric acid from the fermentation process by which citric acid is produced industrially.[2] The citric acid in the broth solution is neutralized by calcium hydroxide, precipitating insoluble calcium citrate. This is then filtered off from the rest of the broth and washed to give clean calcium citrate.

3 Ca(OH)2(s) + 2 C6H8O7(l) → Ca3(C6H5O7)2(s) + 6 H2O(l)

The calcium citrate thus produced may be sold as-is, or it may be converted to citric acid using dilute sulfuric acid.

Biological role

In many individuals, bioavailability of calcium citrate is found to be equal to that of the cheaper calcium carbonate.[3] However, alterations to the digestive tract may change how calcium is digested and absorbed. Unlike calcium carbonate, which is basic and neutralizes stomach acid, calcium citrate has no effect on stomach acid.[4] Calcium carbonate is harder to digest than calcium citrate,[4] and calcium carbonate carries a risk of "acid rebound" (the stomach overcompensates by producing more acid),[4] so individuals who are sensitive to antacids or who have difficulty producing adequate stomach acid may choose calcium citrate over calcium carbonate for supplementation. According to recent research into calcium absorption after gastric bypass surgery,[5] calcium citrate may have improved bioavailability over calcium carbonate in Roux-en-Y gastric bypass patients who are taking calcium citrate as a dietary supplement after surgery. This is mainly due to the changes related to where calcium absorption occurs in the digestive tract of these individuals.


  1. 1 2 3 4 Herdtweck, Eberhardt; Kornprobst, Tobias; Sieber, Roland; Straver, Leo; Plank, Johann (2011). "Crystal Structure, Synthesis, and Properties of tri-Calcium di-Citrate tetra-Hydrate [Ca3(C6H5O7)2(H2O)2]·2H2O". Z. Anorg. Allgemeine Chemie. 637 (6): 655–659. doi:10.1002/zaac.201100088.
  2. "Use of Lime in the Chemical Industry". National Lime Association. Archived from the original on 2006-09-29. Retrieved 2006-11-25.
  3. Heaney RP, Dowell MS, Bierman J, Hale CA, Bendich A (2001). "Absorbability and cost effectiveness in calcium supplementation". Journal of the American College of Nutrition. 20 (3): 239–46. doi:10.1080/07315724.2001.10719038. PMID 11444420.| PMID 11444420
  4. 1 2 3 "What you need to know about calcium". Harvard Health Publications. Retrieved 4 August 2014.
  5. Tondapu P, Provost D, Adams-Huet B, Sims T, Chang C, Sakhaee K (June 2009). "Comparison of the Absorption of Calcium Carbonate and Calcium Citrate after Roux-en-Y Gastric Bypass". Obesity Surgery. 19 (9): 1256–1261. doi:10.1007/s11695-009-9850-6. PMID 19437082.
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