Maleic acid

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Structural formula
Structure of maleic acid
Surname Maleic acid
other names
  • ( 2Z ) -But-2-enedioic acid ( IUPAC )
  • cis -butenedioic acid
  • cis -ethylene dicarboxylic acid
  • Toxic acid
  • ( Z ) -butenedioic acid
Molecular formula C 4 H 4 O 4
Brief description

white, crystalline powder with a slightly acidic odor

External identifiers / databases
CAS number 110-16-7
EC number 203-742-5
ECHA InfoCard 100.003.403
PubChem 444266
ChemSpider 392248
DrugBank DB04299
Wikidata Q42038
Molar mass 116.07 g mol −1
Physical state



1.59 g cm −3

Melting point
  • Decomposition> 135 ° C
  • 130.5 ° C
pK s value

1.9 and 6.5

safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary
07 - Warning


H and P phrases H: 302-315-319-335-317
P: 261-280-305 + 351 + 338
Thermodynamic properties
ΔH f 0

−789.4 kJ / mol

As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Maleic acid is the common name for cis -butenedioic acid (also called cis -ethylene dicarboxylic acid or toxilic acid), a dicarboxylic acid . Their salts are called male (in) ate. The isomeric trans form is called fumaric acid .


Maleic acid was first obtained in 1834 from Théophile-Jules Pelouze by heating malic acid . The connection from 1919 was industrially accessible by those of the US company Barrett Co. introduced catalytic gas-phase oxidation of benzene . The name "maleic acid" is derived from malic acid (apple = Latin "malum").

In 1874 the spatial structure was derived from the chemical behavior - the anhydride formation .

Extraction and presentation

Maleic acid industrially by hydration of maleic anhydride at temperatures of 65-85 ° C.

Hydration of maleic anhydride to maleic acid at elevated temperatures

One works continuously in a stirred tank reactor and keeps the temperature in a constant range. This allows the formation of the isomeric fumaric acid to be reduced to less than 0.1%.


Physical Properties

Maleic acid forms colorless crystals at room temperature. Decomposition is observed on heating above 135 ° C. It is readily soluble in water and reacts strongly acidic in it: the biprotonic acid has a pKa 1 of 1.9 and a pKa 2 of 6.5. The compound dissolves very well in water, the solubility increasing sharply with increasing temperature.

Solubility of maleic acid in 100 g of water
temperature in ° C 25th 40 60 97.5
solubility in g per 100 g 78.9 112.3 148.8 392.6

The molar enthalpy of formation is −788.3 kJ mol −1 , the heat of combustion −1358.9 kJ mol −1 . A value of 135.6 J · mol −1 · K −1 or 1.17 J · g −1 · K −1 was determined for the heat capacity at 21 ° C.

Chemical properties

Maleic acid is chemically very reactive with regard to reactions of the carbonyl functions and the double bond. When heated to temperatures above 100 ° C, it changes into maleic anhydride with elimination of water. When dissolved in water, the anhydride then forms maleic acid again. With further heating and with the aid of catalysts, decarboxylation to acrylic acid can be achieved. With prolonged heating to 150 ° C and with UV irradiation, the maleic acid isomerizes to the more stable fumaric acid . All typical carbonyl reactions such as esterifications or aminations can be carried out with maleic acid . However, no acid chloride is formed. Addition of water to the double bond at elevated temperature and increased pressure results in the malic acid, the addition of halogens Dihalogenbernsteinsäuren, a catalytic hydrogenation , the succinic acid . By reaction with ozone is glyoxylic received. When malic acid is heated quickly to 250 ° C, these 2 molecules of water are split off, forming maleic anhydride.

Physiological properties

Maleic acid and its salts are harmful to the kidneys if higher doses are taken orally. This property is used, for example, in the animal model of the color rat to produce the symptoms of De Toni Fanconi syndrome . The proximal tubular cells are specifically damaged. The doses required to induce renal dysfunction are in the range of 200 mg / kg body weight for intraperitoneal administration.


Maleic acid is used for the production of polymers , synthetic resins and maleic acid esters , for refining and dyeing cotton and as an ingredient in decalcifying agents based on sulfamic acid or citric acid , which is intended to counteract rapid re-calcification.

In pharmacology, solutions of the maleates of antihistamines are used as injectable drugs for acute use. In preparative chemistry, maleic acid is often used as an agent for the Diels-Alder reaction .

In dentistry, maleic acid is used in self-etching adhesive systems to condition dentin .

Maleate: Risk of confusion with malonate and malate

Maleate must not be confused with the acid anion of malic acid , the malate ion, or the anion of malonic acid , the malonate .

Web links

Commons : Maleic Acid  - Collection of pictures, videos and audio files
Wiktionary: Maleic acid  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. a b c d e f g Entry on maleic acid in the GESTIS substance database of the IFA , accessed on February 18, 2019(JavaScript required) .
  2. a b c d e f g h K. Lohbeck, H. Haferkorn, W. Fuhrmann, N. Fedke: Maleic and Fumaric Acids. In: Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH Verlag, Weinheim, 2012, doi : 10.1002 / 14356007.a16_053 .
  3. a b A. Reichert: Potentiometric titrations in theory and practice. ( Memento of the original from April 1, 2007 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot /
  4. a b Entry on maleic acid. In: Römpp Online . Georg Thieme Verlag, accessed on January 31, 2019.
  5. Entry on maleic acid in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
  6. David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Standard Thermodynamic Properties of Chemical Substances, pp. 5-25.
  7. Patent EP0864558A1 : Process for producing maleic acid. Published September 16, 1998 , Applicant: The Procter & Gamble Company, Inventor: Christian Dethloff, Barbarino, Sergio.
  8. Timothy R. Felthouse, Joseph C. Burnett, Ben Horrell, Michael J. Mummey, Yeong-Jen Kuo: Maleic Anhydride, Maleic Acid, and Fumaric Acid. In: Kirk-Othmer Encyclopedia of Chemical Technology . Wiley ‐ VCH Verlag GmbH & Co. KGaA., October 18, 2001, p. 9, doi : 10.1002 / 0471238961.1301120506051220.a01.pub2 .
  9. ^ Parks, GS; Huffman, HM: Thermal data on organic compounds. IX. A study of the effect of unsaturation on the heat capacities, entropies and free energies of some hydrocarbons and other compounds in J. Am. Chem. Soc. 52 (1930) 4381-4391, doi : 10.1021 / ja01374a029 .
  10. Beyer-Walter: Textbook of Organic Chemistry , 23rd Edition, p. 356, S. Hirzel Verlag 1998. ISBN 3-7776-0808-4 .
  11. ^ RM Everett, G. Descotes et al.: Nephrotoxicity of pravadoline maleate (WIN 48098-6) in dogs: evidence of maleic acid-induced acute tubular necrosis. In: Fundamental and applied toxicology: official journal of the Society of Toxicology. Volume 21, Number 1, July 1993, pp. 59-65. PMID 8365586 .
  12. Cosmetic Ingredient Review Expert Panel: Final report on the safety assessment of Maleic Acid. In: International journal of toxicology. Volume 26 Suppl 2, 2007, pp. 125-130, doi: 10.1080 / 10915810701351251 . PMID 17613135 (Review).
  13. ^ RA Zager, AC Johnson et al .: Maleate nephrotoxicity: mechanisms of injury and correlates with ischemic / hypoxic tubular cell death. In: American Journal of Physiology - Renal physiology. Volume 294, number 1, January 2008, pp. F187-F197, doi: 10.1152 / ajprenal.00434.2007 . PMID 17942567 .
  14. W. Pfaller, G. Gstraunsthaler, P. Kontanko: nephrotoxicity: Morphology - function relationship. In: Walter G. Guder, Hermann Lang (Hrsg.): Pathobiochemistry and functional diagnosis of the kidney. Springer-Verlag, 2013, ISBN 978-3-642-84384-6 , p. 92 ( limited preview in Google book search).
  15. ^ William B. Jensen: The Origin of the Names Malic, Maleic, and Malonic Acid. In: J. Chem. Educ. 84, 2007, p. 924, doi: 10.1021 / ed084p924 .