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'''Fumaric acid''' is an [[organic compound]] with the formula HO<sub>2</sub>CCH=CHCO<sub>2</sub>H. A white solid, fumaric acid occurs widely in nature. It has a [[fruit]]-like [[taste]] and has been used as a [[food additive]]. Its [[E number]] is E297.<ref name=Ullmann>{{cite book|doi=10.1002/14356007.a16_053|chapter=Maleic and Fumaric Acids|title=Ullmann's Encyclopedia of Industrial Chemistry|year=2000|last1=Lohbeck|first1=Kurt|last2=Haferkorn|first2=Herbert|last3=Fuhrmann|first3=Werner|last4=Fedtke|first4=Norbert|isbn=
</ref> The [[salt (chemistry)|salts]] and [[ester]]s are known as '''fumarates'''. Fumarate can also refer to the {{chem|C|4|H|2|O|4|2−}} ion (in solution). Fumaric acid is the trans isomer of butenedioic acid, while [[maleic acid]] is the cis isomer.
==Biosynthesis and occurrence==
It is produced in [[eukaryotic]] organisms from [[succinate]] in complex 2 of the electron transport chain via the [[enzyme]] [[succinate dehydrogenase]].
Fumaric acid is found in [[fumitory]] (''Fumaria officinalis''), [[bolete]] [[mushroom]]s (specifically ''Boletus fomentarius var. pseudo-igniarius''), [[lichen]], and [[Iceland moss]].
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Fumarate is an [[Reaction intermediate|intermediate]] in the [[citric acid cycle]] used by [[cell (biology)|cells]] to produce energy in the form of [[adenosine triphosphate]] (ATP) from [[food]]. It is formed by the [[oxidation]] of [[succinate]] by the enzyme [[succinate dehydrogenase]]. Fumarate is then converted by the enzyme [[fumarase]] to [[malic acid|malate]].
Human skin naturally produces fumaric acid when exposed to [[sunlight]].<ref>[https://books.google.com/books?id=tWJLUWT06BEC
Fumarate is also a product of the [[urea cycle]].
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===Food===
Fumaric acid has been used as a food acidulant since 1946. It is approved for use as a food additive in the EU,<ref>UK Food Standards Agency: {{cite web |url=http://www.food.gov.uk/safereating/chemsafe/additivesbranch/enumberlist |title=Current EU approved additives and their E Numbers |access-date=2011-10-27}}</ref> USA<ref>US Food and Drug Administration: {{cite web |url=https://www.fda.gov/Food/FoodIngredientsPackaging/FoodAdditives/ucm191033.htm#ftnT |title=Listing of Food Additives Status Part II |website=[[Food and Drug Administration]] |access-date=2011-10-27}}</ref> and Australia and New Zealand.<ref>Australia New Zealand Food Standards Code{{cite web |url=http://www.comlaw.gov.au/Details/F2011C00827 |title=Standard 1.2.4 - Labelling of ingredients |date=8 September 2011 |access-date=2011-10-27}}</ref> As a [[food additive]], it is used as an [[acidity regulator]] and can be denoted by the [[E number]] E297. It is generally used in beverages and [[baking powder]]s for which requirements are placed on purity. Fumaric acid is used in the making of [[wheat tortilla]]s as a food preservative and as the acid in leavening.<ref>{{Cite news|url=https://thechemco.com/chemical/fumaric-acid/|title=Fumaric Acid - The Chemical Company|work=The Chemical Company|access-date=2018-04-22|language=en-US}}</ref> It is generally used as a substitute for [[tartaric acid]] and occasionally in place of [[citric acid]], at a rate of 1 g of fumaric acid to every ~1.5 g of citric acid, in order to add [[Taste#Sourness|sourness]], similarly to the way [[malic acid]] is used. As well as being a component of some artificial vinegar flavors, such as "Salt and Vinegar" flavored potato chips,<ref>{{cite web|url=http://www.seriouseats.com/2012/09/the-best-salt-and-vinegar-chips-tasting-brands-most-acidic.html|title=The Science Behind Salt and Vinegar Chips|first=Serious|last=Eats|website=www.seriouseats.com}}</ref> it is also used as a [[flocculation|coagulant]] in stove-top pudding mixes.
The European Commission Scientific Committee on Animal Nutrition, part of [[Directorate-General for Health and Food Safety|DG Health]], found in 2014 that fumaric acid is "practically non-toxic" but high doses are probably [[Nephrotoxicity|nephrotoxic]] after long-term use.<ref name=ecscfa>European Commission: {{cite web |url=http://ec.europa.eu/food/fs/sc/scan/out112_en.pdf |title=European Commission Report of the Scientific Committee on Animal Nutrition on the Safety of Fumaric Acid |access-date=2014-03-07}}</ref>
===Medicine===
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When fumaric acid is added to their feed, lambs produce up to 70% less methane during digestion.<ref>{{Cite news | url = https://m.phys.org/news/2008-03-scientists-cow-flatulence.html | title = Scientists look to cut cow flatulence | date = March 21, 2008 | publisher = phys.org }}</ref>
===Historic and laboratory routes===
Fumaric acid was first prepared from [[succinic acid]].<ref>Volhard, J. "Darstellung von Maleïnsäureanhydrid" Justus Liebig's Annalen der Chemie 1892, volume 268, page 255-6. {{doi|10.1002/jlac.18922680108}}</ref> A traditional synthesis involves oxidation of [[furfural]] (from the processing of [[maize]]) using [[sodium chlorate|chlorate]] in the presence of a [[vanadium]]-based [[catalyst]].<ref>
==Reactions==
The chemical properties of fumaric acid can be anticipated from its component [[functional group]]s. This weak acid forms a di[[ester]], it undergoes
<!--Fumaric acid does not combust in a [[bomb calorimeter]] under conditions where [[maleic acid]] deflagrates smoothly. For teaching experiments designed to measure the difference in energy between the cis- and trans- isomers, a measured quantity of carbon can be ground with the subject compound and the enthalpy of combustion computed by difference.-->▼
==Safety==
Fumaric acid is required for life. The oral [[LD50]] is 10g/kg.<ref name=Ullmann/>
▲==Synthesis and reactions==
▲Fumaric acid was first prepared from [[succinic acid]].<ref>Volhard, J. "Darstellung von Maleïnsäureanhydrid" Justus Liebig's Annalen der Chemie 1892, volume 268, page 255-6. {{doi|10.1002/jlac.18922680108}}</ref> A traditional synthesis involves oxidation of [[furfural]] (from the processing of [[maize]]) using [[sodium chlorate|chlorate]] in the presence of a [[vanadium]]-based [[catalyst]].<ref>Milas, N. A. "Fumaric Acid" ''Organic Synthesis'' 1943, Collective Volume 2, page 302. [http://www.orgsyn.org/orgsyn/pdfs/CV2P0302.pdf Online version]</ref>
▲Currently, industrial synthesis of fumaric acid is mostly based on [[catalyst|catalytic]] [[isomerisation]] of [[maleic acid]] in aqueous solutions at low p''H''. Maleic acid is accessible in large volumes as a [[hydrolysis]] product of maleic anhydride, produced by catalytic oxidation of [[benzene]] or [[butane]].<ref name=Ullmann/>
▲The chemical properties of fumaric acid can be anticipated from its component [[functional group]]s. This weak acid forms a di[[ester]], it undergoes additions across the [[alkene|double bond]], and it is an excellent [[dienophile]].
▲Fumaric acid does not combust in a [[bomb calorimeter]] under conditions where [[maleic acid]] deflagrates smoothly. For teaching experiments designed to measure the difference in energy between the cis- and trans- isomers, a measured quantity of carbon can be ground with the subject compound and the enthalpy of combustion computed by difference.
==See also==
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[[Category:E-number additives]]
[[Category:Alkene derivatives]]
[[Category:Metabolic intermediates]]
[[Category:Biomolecules]]
[[Category:Carboxylic acid-based monomers]]
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