Maleic acid 2175688 225857615 2008-07-15T18:53:26Z Beatsbox 7262463 /* 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]]