Butyric acid
232345
222001112
2008-06-27T02:12:40Z
68.13.219.81
{{Chembox new
|ImageFile=Butyric-acid-2D-skeletal.png
|ImageSize2=
|ImageFile2=Butyric-acid-3D-balls.png
|ImageSize=
|IUPACName= Butanoic acid
|Section1= {{Chembox Identifiers
| CASNo=107-92-6
| PubChem=264
| SMILES=CCCC(=O)O
| MeSHName=Butyric+acid
}}
|Section2= {{Chembox Properties
| Formula=C<sub>4</sub>H<sub>8</sub>O<sub>2</sub>
| MolarMass=88.1051 g/mol
| Appearance=
| Density=0.96 g/mL
| MeltingPt=-7.9 °C (265.1 K)
| BoilingPt=163.5 °C (436.5 K)
| Solubility=miscible
}}
|Section3= {{Chembox Hazards
| MainHazards=Corrosive; Harmful to aquatic organisms
| FlashPt=72 °C
| Autoignition=452 °C
| RPhrases = 34
| SPhrases = 26 36 45
| RSPhrases =
| RTECS = ES5425000
}}
}}
'''Butyric acid''' (from [[Greek language|Greek]] βούτυρος = ''butter''), also known under the systematic name '''butanoic acid''', is a [[carboxylic acid]] with the structural formula [[Carbon|C]][[Hydrogen|H]]<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>-[[Carboxyl group|COOH]]. It is found in rancid [[butter]], [[parmesan cheese]], [[vomit]], and [[body odor]] and has an unpleasant [[odor|smell]] and acrid [[taste]], with a sweetish aftertaste (similar to [[diethyl ether|ether]]). Butyric acid can be detected by [[mammal]]s with good scent detection abilities such as [[dog]]s at 10 [[ppb]], whereas [[human]]s can detect it in concentrations above 10 [[Parts per million|ppm]].
==Chemistry==
Butyric acid is a [[fatty acid]] occurring in the form of [[esters]] in animal fats and plant oils. The [[glyceride]] of butyric acid makes up 3% to 4% of butter. When butter goes rancid, butyric acid is liberated from the glyceride by [[hydrolysis]] leading to the unpleasant odor. It is an important member of the fatty acid sub-group called [[short chain fatty acids]]. Butyric acid is a [[weak acid]] with a [[pKa]] of 4.82, similar to [[acetic acid]] which has pKa 4.76.<ref>{{cite web|url=http://www.linkan.se/files/pdf/product_sheets/INVE/adimix_presentation.pdf|title=Adimix Sodium Butanoate information}}</ref> The similar strength of these acids results from their common -CH<sub>2</sub>COOH terminal structure.<ref>{{cite web|url=http://web.chem.ucla.edu/~harding/tutorials/acids_and_bases/pKa_table.html|title=Using the pKa table}}</ref> Butyric acid has density 0.96 g/cm<sup>3</sup> and molecular mass 88.1051; thus pure butyric acid is 10.9 [[Concentration#Molarity|molar]].
The acid is an oily colorless liquid that freezes at -8 [[Celsius|°C]]; it boils at 164 °C. It is easily soluble in [[water]], [[ethanol]], and [[ether]], and is precipitated out of its aqueous solution by the addition of [[calcium chloride]]. [[Potassium dichromate]] and [[sulfuric acid]] oxidize it to [[carbon dioxide]] and [[acetic acid]], while alkaline [[potassium permanganate]] oxidizes it to carbon dioxide. The calcium salt, Ca(C<sub>4</sub>H<sub>7</sub>O<sub>2</sub>)<sub>2</sub>·H<sub>2</sub>O, is less soluble in hot water than in cold.
Butyric acid has a [[structural isomer]] called [[isobutyric acid]] (2-methylpropanoic acid).
==Production==
It is industrially prepared by the fermentation of [[sugar]] or [[starch]], brought about by the addition of putrefying [[cheese]], with [[calcium carbonate]] added to neutralize the acids formed in the process. The butyric fermentation of starch is aided by the direct addition of ''[[Bacillus subtilis]]''. Salts and esters of the acid are called [[butanoate]]s.
Butyric acid or fermentation butyric acid is also found as a hexyl [[ester]] (hexyl butanoate) in the oil of ''Heracleum giganteum'' (a type of [[cow parsnip]]) and as an octyl ester (octyl butanoate) in [[parsnip]] (''Pastinaca sativa''); it has also been noticed in the fluids of the flesh and in perspiration.
==Uses==
Butyric acid is used in the preparation of various butanoate esters. Low-molecular-weight esters of butyric acid, such as [[methyl butanoate]], have mostly pleasant aromas or tastes. As a consequence, they find use as food and perfume additives. They are also used in organic laboratory courses, to teach the [[Hermann Emil Fischer|Fischer]] esterification reaction.
==Biological functionality==
=== Butanoate fermentation ===
Butanoate is produced as end-product of a fermentation process solely performed by obligate [[Anaerobic organism|anaerobic]] [[bacteria]]. Fermented [[Kombucha]] "tea" includes butyric acid as a result of the fermentation. This fermentation pathway was discovered by [[Louis Pasteur]] in [[1861]]. Examples of butanoate-producing [[species]] of bacteria:
* ''[[Clostridium acetobutylicum]]''
* ''[[Clostridium butyricum]]''
* ''[[Clostridium kluyveri]]''
* ''[[Clostridium pasteurianum]]''
* ''[[Fusobacterium nucleatum]]''
* ''[[Butyrivibrio fibrisolvens]]''
* ''[[Eubacterium limosum]]''
The pathway starts with the [[glycolysis|glycolytic]] cleavage of [[glucose]] to two [[molecule]]s of [[pyruvate]], as happens in most organisms. Pyruvate is then [[oxidation|oxidized]] into [[acetyl coenzyme A]] using a unique mechanism that involves an [[enzyme]] system called [[pyruvate-ferredoxin oxidoreductase]]. Two molecules of [[carbon dioxide]] (CO<sub>2</sub>) and two molecules of elemental [[hydrogen]] (H<sub>2</sub>) are formed as wastes products from the cell. Then:
{| class="wikitable"
| '''Action''' || '''Responsible enzyme'''
|-
| Acetyl coenzyme A converts into [[acetoacetyl coenzyme A]] || [[acetyl-CoA-acetyl transferase]]
|-
| Acetoacetyl coenzyme A converts into [[β-hydroxybutyryl CoA]] || [[β-hydroxybutyryl-CoA dehydrogenase]]
|-
| β-hydroxybutyryl CoA converts into [[crotonyl CoA]] || [[crotonase]]
|-
| Crotonyl CoA converts into [[butyryl CoA]] (CH<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>C=O-CoA) || [[butyryl CoA dehydrogenase]]
|-
| A [[phosphate]] group replaces CoA to form [[butyryl phosphate]] || [[phosphobutyrylase]]
|-
| The phosphate group joins [[Adenosine diphosphate|ADP]] to form [[Adenosine triphosphate|ATP]] and [[butyrate]] || [[butyrate kinase]]
|}
ATP is produced, as can be seen, in the last step of the fermentation. Three molecules of ATP are produced for each glucose molecule, a relatively high yield. The balanced equation for this fermentation is:
'''C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> → C<sub>4</sub>H<sub>8</sub>O<sub>2</sub> + 2CO<sub>2</sub> + 2H<sub>2</sub>'''
=== Acetone and butanol fermentation ===
Several species form [[acetone]] and [[butanol]] in an alternative pathway, which starts as butyrate fermentation. Some of these species are:
* ''[[Clostridium acetobutylicum]]'': the most prominent acetone and butanol producer, used also in industry
* ''[[Clostridium beijerinckii]]''
* ''[[Clostridium tetanomorphum]]''
* ''[[Clostridium aurantibutyricum]]''
These bacteria begin with butanoate fermentation as described above, but, when the [[pH]] drops below 5, they switch into butanol and acetone production in order to prevent further lowering of the pH. Two molecules of butanol are formed for each molecule of acetone.
The change in the pathway occurs after acetoacetyl CoA formation. This intermediate then takes two possible pathways:
* Acetoacetyl CoA → acetoacetate → acetone, or
* Acetoacetyl CoA → butyryl CoA → [[butanal]] → butanol.
=== Butyric acid function/activity ===
Highly-fermentable fibers like [[oat bran]], [[pectin]], and [[guar]] are transformed by [[gut flora|colonic bacteria]] into [[short chain fatty acid]]s including butyrate.
Butanoate has diverse and, it seems, paradoxical effects on [[cell growth |cellular proliferation]], [[apoptosis]] and [[cellular differentiation |differentiation]] that may be either pro-[[neoplastic]] or anti-neoplastic, depending upon factors such as the level of exposure, availability of other metabolic substrate, and the intracellular milieu. Butanoate is thought by some to be protective against [[colon cancer]]. However, not all studies support a chemopreventive effect, and the lack of agreement (particularly between [[in vivo]] and [[in vitro]] studies) on butyrate and colon cancer has been termed the "butyrate paradox." There are many reasons for this discrepant effect, including differences between the ''in vitro'' and ''in vivo'' environments, the timing of butanoate administration, the amount administered, the source (usually dietary fiber) as a potential confounder, and an interaction with dietary fat. Together, the studies suggest that the chemopreventive benefits of butanoate depend in part on amount, time of exposure with respect to the tumorigenic process, and the type of fat in the diet.<ref>[http://jn.nutrition.org/cgi/content/full/134/2/479 Microbial Degradation Products Influence Colon Cancer Risk: the Butyrate Controversy - Lupton 134 (2): 479 - Journal of Nutrition<!-- Bot generated title -->]</ref> Low carbohydrate diets like the [[Atkins diet]] are known to reduce the amount of butanoate produced in the colon.
Butyric acid has been associated with the ability to inhibit the function of [[histone deacetylase]] enzymes, thereby favouring an acetylated state of [[histone]]s in the cell. Acetylated histones have a lower affinity for [[DNA]] than non-acetylated histones, due to the neutralisation of [[electrostatic]] charge interactions. In general, it is thought that [[transcription factors]] will be unable to access regions where histones are tightly associated with DNA (ie non-acetylated, e.g., heterochromatin). Therefore, it is thought that butyric acid enhances the transcriptional activity at promoters, which are typically silenced/downregulated due to histone deacetylase activity.
==References==
{{reflist}}
==See also==
*[[Indole-3-butyric acid]]
==External links==
* [http://www.cdc.gov/niosh/ipcsneng/neng1334.html International Chemical Safety Card 1334]
* [http://jn.nutrition.org/cgi/content/full/134/2/479 2004 review of the scientific evidence on butanoate/butyrate vs. colon cancer]
''This article incorporates information from the 1911 encyclopedia.''
{{Fatty acids}}
[[Category:flavors]]
[[Category:Carboxylic acids]]
[[Category:Fatty acids]]
[[Category:Metabolism]]
[[Category:Butyrates]]
[[Category:Acids]]
[[Category:Foul-smelling chemicals]]
[[cs:Kyselina máselná]]
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[[es:Ácido butírico]]
[[fr:Acide butanoïque]]
[[is:Smjörsýra]]
[[it:Acido butirrico]]
[[he:חומצה בוטירית]]
[[la:Acidum butyricum]]
[[lv:Sviestskābe]]
[[nl:Boterzuur]]
[[ja:酪酸]]
[[no:Smørsyre]]
[[pl:Kwas masłowy]]
[[pt:Ácido butanóico]]
[[ru:Масляная кислота]]
[[sk:Kyselina maslová]]
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