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Maleic acid or (Z)-butenedioic acid or cis-butenedioic acid or malenic acid or maleinic acid or toxilic acid is an organic compound
Organic compound

An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered Inorganic compound....
 that is a dicarboxylic acid
Dicarboxylic acid

Dicarboxylic acids are organic compounds that are substituted with two carboxylic acid functional groups. In molecular formulae for dicarboxylic acids, these groups are often written as HOOC-R-COOH, where R is usually an alkane, alkene, or alkyne group....
 (molecule with two carboxyl groups). The molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
 consists of an ethylene
Ethylene

Ethylene is the chemical compound with the formula C2H4. It is the simplest alkene. Because it contains a carbon-carbon double bond, ethylene is called an unsaturated hydrocarbon or an olefin....
 group flanked by two carboxylic acid groups. Maleic acid is the cis isomer of butenedioic acid, whereas fumaric acid
Fumaric acid

Fumaric acid is the chemical compound with the formula HO2CCH=CHCO2H. This white crystalline compound is one of two isomeric unsaturated dicarboxylic acids, the other being maleic acid wherein the carboxylic acid groups are cis....
 is the trans isomer. Maleic acid is the less stable molecule: e.g., the difference in heat of combustion
Heat of combustion

The heat of combustion is the energy released as heat when one mol of a compound undergoes complete combustion with oxygen. The chemical reaction is typically a hydrocarbon reacting with oxygen to form carbon dioxide, water and heat....
 is 22.7 kJ/mol.






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Maleic acid or (Z)-butenedioic acid or cis-butenedioic acid or malenic acid or maleinic acid or toxilic acid is an organic compound
Organic compound

An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered Inorganic compound....
 that is a dicarboxylic acid
Dicarboxylic acid

Dicarboxylic acids are organic compounds that are substituted with two carboxylic acid functional groups. In molecular formulae for dicarboxylic acids, these groups are often written as HOOC-R-COOH, where R is usually an alkane, alkene, or alkyne group....
 (molecule with two carboxyl groups). The molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
 consists of an ethylene
Ethylene

Ethylene is the chemical compound with the formula C2H4. It is the simplest alkene. Because it contains a carbon-carbon double bond, ethylene is called an unsaturated hydrocarbon or an olefin....
 group flanked by two carboxylic acid groups. Maleic acid is the cis isomer of butenedioic acid, whereas fumaric acid
Fumaric acid

Fumaric acid is the chemical compound with the formula HO2CCH=CHCO2H. This white crystalline compound is one of two isomeric unsaturated dicarboxylic acids, the other being maleic acid wherein the carboxylic acid groups are cis....
 is the trans isomer. Maleic acid is the less stable molecule: e.g., the difference in heat of combustion
Heat of combustion

The heat of combustion is the energy released as heat when one mol of a compound undergoes complete combustion with oxygen. The chemical reaction is typically a hydrocarbon reacting with oxygen to form carbon dioxide, water and heat....
 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
Intramolecular

Intramolecular in chemistry describes a process or characteristic limited within the structure of a single molecule; a property or phenomenon limited to the extent of a single molecule....
 hydrogen bond
Hydrogen bond

A hydrogen bond is the attractive force between one electronegative atom and a hydrogen covalently bonded to another electronegative atom. It results from a dipole-dipole force with a hydrogen atom bonded to nitrogen, oxygen or fluorine ....
ing that takes place at the expense of intermolecular interactions.

Maleic acid should not be confused with malic acid
Malic acid

Malic acid is an organic compound with the formula HO2CCH2CHOHCO2H. This dicarboxylic acid is the active ingredient in many sour or tart foods....
 or malonic acid
Malonic acid

Malonic acid is a dicarboxylic acid with structure carbonhydrogen22. The ionised form of malonic acid, as well as its esters and salts, are known as malonates....
, both of which are different types of dicarboxylic acids.

Synthesis

In industry, maleic acid is derived from maleic anhydride
Maleic anhydride

Maleic anhydride is an organic compound with the formula C4H2O3. In its pure state it is a colourless or white solid with an acrid odour....
 by hydrolysis
Hydrolysis

Hydrolysis is a chemical reaction during which one or more water are split into hydrogen and hydroxide ions which may go on to participate in further reactions....
. Maleic anhydride is produced from benzene
Benzene

Benzene, or benzol, is an organic compound chemical compound and a known carcinogen with the molecular formula Carbon6Hydrogen6....
 or butane
Butane

Butane, also called n-butane, is the unbranched alkane with four carbon atoms, CH3CH2CH2CH3....
 in an 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
    Bromine

    Bromine , , meaning "stench " ), is a chemical element with the symbol Br and atomic number 35. A halogen element, bromine is a reddish-brown Volatility liquid at Standard conditions for temperature and pressure that is intermediate in reactivity between chlorine and iodine....
     . Light converts elemental bromine into a bromine 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
    Fumaric acid

    Fumaric acid is the chemical compound with the formula HO2CCH=CHCO2H. This white crystalline compound is one of two isomeric unsaturated dicarboxylic acids, the other being maleic acid wherein the carboxylic acid groups are cis....
     through the process of heating the maleic acid in 12 molar
    Concentration

    In chemistry, concentration is the measure of how much of a given chemical substance there is mixed with another substance. This can apply to any sort of chemical mixture, but most frequently the concept is limited to homogeneous solutions, where it refers to the amount of solute in the solvent....
     hydrochloric acid
    Hydrochloric acid

    Hydrochloric acid is the solution of hydrogen chloride in water. It is a highly corrosive, strong acid mineral acid and has major industrial uses....
      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 catalytic
    Catalysis

    Catalysis is the process in which the reaction rate of a chemical reaction is either increased or decreased by means of a chemical substance known as a catalyst....
     isomerization with mineral acid
    Mineral acid

    A mineral acid is an acid derived from one or more inorganic chemistry compounds. A mineral acid does not contain any carbon atoms and all mineral acids release hydrogen ions when dissolved in water....
    s, bromate
    Bromate

    The bromate ion, , is a bromine-based oxyanion. A bromate is a chemical compound that contains this ion. Examples of bromates include sodium bromate, , and potassium bromate, ....
    s, or thiourea
    Thiourea

    Thiourea is an organic compound of carbon, nitrogen, sulfur and hydrogen, with the chemical formula CarbonSulfurNitrogen2Hydrogen4 or 2CarbonSulfur....
     . 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
    Glyoxylic acid

    Glyoxylic acid or oxoacetic acid is an organic compound with the chemical formula C2H2O3.Glyoxylic acid is an aldehyde and a carboxylic acid....
     by ozonolysis
    Ozonolysis

    Ozonolysis is the cleavage of an alkene or alkyne with ozone to form organic compounds in which the multiple carbon-carbon bond has been replaced by a double bond to oxygen....
     .
  • Maleic acid is converted into maleic anhydride
    Maleic anhydride

    Maleic anhydride is an organic compound with the formula C4H2O3. In its pure state it is a colourless or white solid with an acrid odour....
     by dehydration
    Dehydration reaction

    In chemistry, a dehydration reaction is usually defined as a chemical reaction that involves the loss of water from the reacting molecule. Dehydration reactions are a subset of elimination reactions....
    , to malic acid
    Malic acid

    Malic acid is an organic compound with the formula HO2CCH2CHOHCO2H. This dicarboxylic acid is the active ingredient in many sour or tart foods....
     by hydration
    Hydration reaction

    In organic chemistry, a hydration reaction is a chemical reaction in which a hydroxyl group and a hydrogen cation are added to the two carbon atoms covalent bonded together in the carbon-carbon double bond which makes up an alkene functional group....
    , and to succinic acid
    Succinic acid

    Succinic acid is a dicarboxylic acid. Succinate plays a biochemical role in the citric acid cycle....
     by hydrogenation
    Hydrogenation

    Hydrogenation is the chemical reaction that results from the addition of hydrogen . The process is usually employed to a redox or Saturation organic compounds....
     (ethanol
    Ethanol

    Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatility , flammable, colorless liquid....
     / Palladium on carbon
    Palladium on carbon

    Palladium on carbon, often referred to as Pd/C, is a form of palladium used for catalysis. It is usually used for catalytic hydrogenations in organic chemistry....
    ) . It reacts with thionyl chloride
    Thionyl chloride

    Thionyl chloride is an inorganic compound with the chemical formula SulfurOxygenChlorine2. It is a reactive chemical reagent used in chlorination chemical reaction....
     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. The maleate ion is useful in biochemistry
Biochemistry

Biochemistry is the study of the chemistry processes in living organisms. It deals with the structure and function of cellular components such as proteins, carbohydrates, lipids, nucleic acids and other biomolecules....
 as an inhibitor of transaminase reactions. Maleic acid ester
Ester

An ester is an often Aroma compound organic chemistry or partially organic compound formed by the reaction between an acid and an alcohol or aromatic alcohol with the elimination of water....
s are also called maleates, for instance dimethyl maleate
Dimethyl maleate

Dimethyl maleate is an organic compound with the formula C6H8O4. It is the -isomer of the dimethyl ester of maleic acid....
.

External links

  • * (from the University of Regensburg
    University of Regensburg

    The University of Regensburg, situated in Regensburg, in Bavaria, Germany, was founded on July 18 1962 by the Bavarian parliament. Bavaria's fourth university saw its first lectures during the 1967-68 winter semester , initially housing a faculty of Law and Business Sciences as well as a faculty of Philosophy....
    , about pH, solubility and melting point)