Kojic acid

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Kojic acid
Kojic acid sample.jpg
OTC kojic acid, slightly impure.
Kojic Acid structure.png
Chemical structure of kojic acid.
IUPAC name
Other names
Molar mass 142.11 g/mol
Appearance White solid
Odor Tree bark-like
Density 1.58 g/cm3 (20 °C)[1]
Melting point 153.5 °C (308.3 °F; 426.6 K) [3]
Boiling point 180 °C (356 °F; 453 K) (decomposes)
9.23 g/100 ml (20 °C)[2]
Solubility Soluble in acetone, DMSO, ethanol, methanol
Slightly soluble in benzene, chloroform, diethyl ether, ethyl acetate, pyridine
Vapor pressure 3.21·10-6 mmHg at 25 °C
Acidity (pKa) 9.40
Safety data sheet Sigma-Aldrich
Lethal dose or concentration (LD, LC):
1,000 mg/kg (rat, oral)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Kojic acid is an organic compound, a chelation agent produced by several species of fungi, especially Aspergillus oryzae, known in Japan as koji ("steamed rice"), from which the said compound got its name. Chemically, kojic acid is a γ-pyrone.



Kojic acid forms a bright red complex with ferric ions. The red color persists even at a dilution 1:200,000. This property permits the estimation of kojic acid by colorimetry.[4]

Salts of kojic acid are called kojates. Kojic acid forms stable complexes of metal kojates via reaction of kojic acid with metal acetate salts such as tin, beryllium, zinc, copper, nickel, cobalt, iron, manganese, chromium, gold, palladium, indium, gallium, vanadium, and aluminium. Tris(kojic acid)aluminium(III) and -gallium(III) complexes have lipid solubility and have been shown to cross the blood-brain barrier in tests.


Kojic acid is a colorless solid. It is soluble in water and a few organic solvents, like acetone, ethanol and methanol.[5] Impure samples appear slight beige or yellowish.


Kojic acid is sold by soapmaking suppliers and other natural care shops. Can be cheaply bought online.


Kojic acid is a by-product in the fermentation process of malting rice caused by the Aspergillus oryzae fungus, process used in the manufacturing of sake, the Japanese rice wine.

Purification an be done by recrystallization from acetone, ethanol-ether, and methanol-ethyl acetate. Sublimation at low pressure, between 150–200 °C is another route.


  • Make metal complexes
  • Make red complex with Fe3+
  • Gravimetric determination of copper
  • Food additive to prevent browning of food
  • Make skin lightning products



Kojic acid doesn't appear to be toxic. In acute, chronic, reproductive and genotoxicity studies, kojic acid was not found to pose high toxicity. Due to slow absorption into the circulation from human skin, it does not reach the threshold at tumor promotion and weak carcinogenicity effects were only suspected.

Kojic acid it's a slight irritant due to its ability to lighten skin.


In closed bottles, away from oxidizers.


No special disposal is required, can be dumped in trash or down the drain.


  1. Li, Ying; Teng, Zi; Parkin, Kirk L.; Wang, Qin; Zhang, Qingli; Luo, Wei; Ma, Deyun; Zhao, Mouming; Journal of Agricultural and Food Chemistry; vol. 62; nb. 33; (2014); p. 8392 - 8401
  2. http://www.t3db.ca/toxins/T3D3769
  3. Lide, D.R. CRC Handbook of Chemistry and Physics 88TH Edition 2007-2008. CRC Press, Taylor & Francis, Boca Raton, FL 2007, p. 3-292
  4. T. Yabuta, Orig. Com. 8th Intern. Congr. Appl. Chem. (Appendix), 26, 455 (1912); Chem. Abstracts, 7, 2191 (1913)
  5. https://www.sciencedirect.com/science/article/pii/S0096533208601186

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