Acyl chloride
581370
219091241
2008-06-13T15:01:59Z
152.78.199.200
/* Synthesis */
[[Image:Acyl-chloride.png|thumb|150px|General chemical structure of an acyl chloride]]
In [[organic chemistry]], an '''acyl chloride''' (or '''acid chloride''') is an [[organic compound]] which is a reactive derivative of a [[carboxylic acid]]. As part of its molecular structure, an acyl chloride has the reactive [[functional group]] '''-[[Carbonyl|CO]]-[[Chlorine|Cl]]'''. An acyl chloride has the general formula RCOCl where R is an [[organic radical]] group.
[[Image:Acetyl-chloride.png|100px|Example of an acyl chloride:<br> acetyl chloride|left|thumb]]
Acyl chlorides are a subset of [[acyl halides]] and undergo many of the [[chemical reaction]]s mentioned under [[acyl halide]]. A specific example of an acyl chloride is [[acetyl chloride]] ([[IUPAC]] name: ethanoyl chloride) CH<sub>3</sub>COCl. <br style="clear:both;">
==Chemical reactions==
Acyl chlorides are very reactive. The presence of the [[chlorine]] on the [[carbonyl]] carbon makes it a very good [[electrophile]], since both the [[oxygen]] and [[chlorine]] are strongly [[electron]] withdrawing, giving the carbon a large partial positive charge. This means even a weak [[nucleophile]] can attack the carbon. Since a [[chloride]] ion is a good leaving group, it will be readily replaced with the nucleophile. Acyl chlorides can be used to prepare any [[carboxylic acid]] derivative: an acid [[anhydride]], an [[ester]] or an [[amide]] by reacting acid chlorides with: a salt of a [[carboxylic acid]], an [[alcohol]], or an [[amine]] respectively. Acid chlorides will also react with [[water]] or a [[Gilman reagent]] (lithium diorganocopper compound). In most of these reactions, HCl ([[hydrogen chloride]] or [[hydrochloric acid]]) is also formed from the [[chlorine]] in the acyl chloride combining with a [[hydrogen]] from the reactant.
For example:
:R-COCl + HO-H → R-COOH + HCl
Acyl chlorides must also be reacted in anhydrous conditions to prevent the hydrolysis of acyl chloride by the moisture in the air.
With carbon nucleophiles such as [[Grignard reagent]]s, acyl chlorides generally react first to the [[ketone]] and then with a second equivalent to the tertiary [[alcohol]]. A notable exception is the reaction of acyl halides with certain [[organocadmium]] reagents which stops at the ketone stage.
Acid chlorides of aromatic acids are generally less reactive those of alkyl acids and thus somewhat more rigorous conditions are required for reaction.
==Hazards==
Because acyl chlorides are such reactive compounds, they are generally [[toxicity|toxic]] and special precautions should be taken while handling them. They are [[lachrymatory]] chemicals because they can react with water at the surface of the eye producing hydrochloric and organic acids irritating to the eye. Similar problems can result if one inhales acyl chloride vapors.
==Synthesis==
Acyl chlorides are often prepared by reacting a carboxylic acid with [[thionyl chloride]], in most cases a couple of drops of N,N'-Dimethylformamide are added to catalyse the reaction.
:R-COOH + SOCl<sub>2</sub> → R-COCl + SO<sub>2</sub> + HCl
The [[sulfur dioxide]] (SO<sub>2</sub>) and [[hydrogen chloride]] (HCl) generated are both gases which can leave the reaction vessel, driving the reaction forward. They are also both [[toxic]] gases.
Acyl chlorides can also be prepared using certain [[phosphorus chloride]] [[reagent]]s such as [[phosphorus trichloride]] or [[phosphorus pentachloride]]:
:R-COOH + PCl<sub>5</sub> → R-COCl + POCl<sub>3</sub> + HCl
==References==
{{Unreferenced|date=May 2008}}
<References/>
[[Category:Acyl chlorides|*]]
[[da:Syrechlorid]]
[[mk:Ацил хлорид]]
[[nl:Zuurchloride]]
[[pt:Cloreto de acila]]
[[ru:Хлорангидриды карбоновых кислот]]
[[sv:Syraklorid]]
[[zh:酰氯]]