Maleic acid
2175688
225857615
2008-07-15T18:53:26Z
Beatsbox
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/* Reactions */
{{Distinguish|Malic acid}}
{{Chembox new
| Name = Maleic acid
| ImageFile = Maleic-acid-2D-skeletal-A.png
| ImageSize = 200px
| ImageName = Skeletal formula of maleic acid
| ImageFile1 = Maleic-acid-3D-balls-A.png
| ImageSize1 = 200px
| ImageName1 = Ball-and-stick model of the maleic acid molecule
| ImageFile2 = Maleic-acid-3D-vdW-A.png
| ImageSize2 = 200px
| ImageName2 = Space-filling model of the maleic acid molecule
| IUPACName = Maleic acid<br />(''Z'')-Butenedioic acid
| Section1 = {{Chembox Identifiers
| SMILES = OC(=O)C=CC(=O)O
| CASNo = 110-16-7
| EINECS = 203-742-5
| RTECS = OM9625000
}}
| Section2 = {{Chembox Properties
| Formula = C<sub>4</sub>H<sub>4</sub>O<sub>4</sub>
| MolarMass = 116.1 g/mol
| Appearance = white solid
| Density = 1.59 g/cm³, solid
| Solubility = 78 g/100 ml (25 °C)
| MeltingPt = 131-139°C ''decomposes''
| BoilingPt = 135 °C ''decomp.''
| pKa = p''k''<sub>a1</sub> = 1.97, p''k''<sub>a2</sub> = 6.07
}}
| Section3 = {{Chembox Structure
| Dipole =
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS = [http://www.jtbaker.com/msds/englishhtml/m0325.htm MSDS from J. T. Baker]
| EUClass = Harmful ('''Xn''')
| RPhrases = {{R22}}, {{R36/37/38}}
| SPhrases = {{S2}}, {{S26}}, {{S28}}, {{S37}}
| FlashPt =
}}
| Section8 = {{Chembox Related
| Function = [[dicarboxylic acids]]
| OtherFunctn = [[Fumaric acid]]<br />[[Succinic acid]]
| OtherCpds = [[Maleic anhydride]]<br />[[Maleimide]]
}}
}}
'''Maleic acid''' or '''(''Z'')-butenedioic acid''' or '''''cis''-butenedioic acid''' or '''malenic acid''' or '''maleinic acid''' or '''toxilic acid''' is an [[organic compound]] that is a [[dicarboxylic acid]] (molecule with two [[carboxyl]] groups). The [[molecule]] consists of an [[ethylene]] group flanked by two carboxylic acid groups. Maleic acid is the [[cis isomer]] of butenedioic acid, whereas [[fumaric acid]] is the ''trans'' isomer. The cis isomer is the less stable one of the two; the difference in [[heat of combustion]] is 22.7 kJ/mol. The physical properties of maleic acid are very different from those of fumaric acid. Maleic acid is soluble in water, whereas fumaric acid is not; and the melting point of maleic acid (130 - 139 °C) is also much lower than that of fumaric acid (287 °C). Both properties of maleic acid can be explained on account of the [[intramolecular]] [[hydrogen bond]]ing<ref>{{cite journal | author= M. N. G James, G. J. B Williams| title= A Refinement of the Crystal Structure of Maleic Acid | journal=Acta Crystallographica | year= 1974 | volume=B30 (5) | pages=1249–1275 | doi= 10.1107/S0567740874004626 }}</ref> that takes place at the expense of intermolecular interactions.
Maleic acid should not be confused with [[malic acid]] or [[malonic acid]], both of which are different types of dicarboxylic acids. In biology the compound goes by the name [[ionised]] [[maleate]].
==Synthesis==
In industry, maleic acid is derived from [[maleic anhydride]] by [[hydrolysis]]. Maleic anhydride is produced from [[benzene]] or [[butane]] in an [[organic oxidation|oxidation]] process.
==Reactions==
* [[Isomerization]]. Maleic acid and fumaric acid can normally not be interconverted because rotation around a carbon carbon [[double bond]] is not energetically favourable. In the laboratory, conversion of the cis isomer into the trans isomer is possible by application of light and a small amount of [[bromine]] <ref>[http://www.uni-regensburg.de/Fakultaeten/nat_Fak_IV/Organische_Chemie/Didaktik/Keusch/D-Mal_Isom-e.htm Light isomerization experiment] (from the [[University of Regensburg]], with video)</ref>. Light converts elemental bromine into a bromine [[free-radical|radical]], which attacks the alkene in a [[radical addition]] reaction to a bromo-alkane radical; and now single bond rotation is possible. The bromine radicals recombine and fumaric acid is formed. In another method (used as a classroom demonstration), maleic acid is transformed into [[fumaric acid]] through the process of heating the maleic acid in 12 [[Concentration#Molarity|molar]] [[hydrochloric acid]] {{Fact|date=November 2007}} solution. Reversible addition (of H+) leads to free rotation about the central C-C bond and formation of the more stable and less soluble fumaric acid. In industry, fumaric acid is also produced from maleic acid by [[catalysis|catalytic]] [[isomerization]] with [[mineral acid]]s, [[bromate]]s, or [[thiourea]] {{Fact|date=November 2007}}. Again the large difference in water solubility makes fumaric acid purification easy.
* Maleic acid is an industrial raw material for the production of [[glyoxylic acid]] by [[ozonolysis]] <ref>[http://www.dsm.com/en_US/html/dfc/rds_oxidation.htm DSM glyoxylic acid production]</ref>.
* Maleic acid is converted into [[maleic anhydride]] by [[Dehydration reaction|dehydration]], to [[malic acid]] by [[Hydration reaction|hydration]], and to [[succinic acid]] by [[hydrogenation]] ([[ethanol]] / [[Palladium on carbon]]) <ref>''Catalytic Hydrogenation of Maleic Acid at Moderate Pressures A Laboratory Demonstration'' Kwesi Amoa 1948 [[Journal of Chemical Education]] • Vol. 84 No. 12 December '''2007'''</ref>. It reacts with [[thionyl chloride]] or [[phosphorus pentachloride]] to give the '''maleic acid chloride''' (it is not possible to isolate the mono acid chloride).
* Maleic acid is a reactant in many [[Diels-Alder]] reactions.
==Maleates==
The '''maleate ion''' is the ionised form of maleic acid. It is of importance to [[biochemistry]]. The maleate ion is useful in biochemistry as an inhibitor of transaminase reactions. Maleic acid [[ester]]s are also called maleates, for instance [[dimethyl maleate]].
==References==
{{Reflist}}
==External links==
{{commons|Maleic acid|Maleic acid}}
*[http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc11/icsc1186.htm International Chemical Safety Card 1186]
*{{ecb}}
* [http://www.uni-regensburg.de/Fakultaeten/nat_Fak_IV/Organische_Chemie/Didaktik/Keusch/chembox_diprotic_tit-e.htm Titration of Fumaric and Maleic Acid] (from the [[University of Regensburg]], about pH, solubility and melting point)
[[Category:Dicarboxylic acids]]
[[ca:Àcid maleic]]
[[de:Maleinsäure]]
[[fr:Acide maléique]]
[[it:Acido maleico]]
[[lv:Maleīnskābe]]
[[nl:Maleïnezuur]]
[[ja:マレイン酸]]
[[pl:Kwas maleinowy]]
[[pt:Ácido maléico]]
[[fi:Maleiinihappo]]
[[sv:Maleinsyra]]
[[zh:馬來酸]]