- Acyl chloride
organic chemistry, an acyl chloride (or acid chloride) is an organic compoundwhich is a reactive derivative of a carboxylic acid. As part of its molecular structure, an acyl chloride has the reactive functional group-CO-Cl. An acyl chloride has the general formula RCOCl where R is an organic radicalgroup.
Acyl chlorides are a subset of
acyl halides and undergo many of the chemical reactions mentioned under acyl halide. A specific example of an acyl chloride is acetyl chloride( IUPACname: ethanoyl chloride) CH3COCl.
Acyl chlorides are very reactive. The presence of the
chlorineon the carbonylcarbon makes it a very good electrophile, since both the oxygenand chlorineare strongly electronwithdrawing, giving the carbon a large partial positive charge. This means even a weak nucleophilecan attack the carbon. Since a chlorideion is a good leaving group, it will be readily replaced with the nucleophile. Acyl chlorides can be used to prepare any carboxylic acidderivative: an acid anhydride, an esteror an amideby reacting acid chlorides with: a salt of a carboxylic acid, an alcohol, or an aminerespectively. Acid chlorides will also react with wateror a Gilman reagent(lithium diorganocopper compound). In most of these reactions, HCl ( hydrogen chlorideor hydrochloric acid) is also formed from the chlorinein the acyl chloride combining with a hydrogenfrom the reactant.
: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 reagents, acyl chlorides generally react first to the ketoneand then with a second equivalent to the tertiary alcohol. A notable exception is the reaction of acyl halides with certain organocadmiumreagents 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.
Because acyl chlorides are such reactive compounds, they are generally toxic and special precautions should be taken while handling them. They are
lachrymatorychemicals 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.
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 + SOCl2 → R-COCl + SO2 + HCl
sulfur dioxide(SO2) and hydrogen chloride(HCl) generated are both gases which can leave the reaction vessel, driving the reaction forward. They are also both toxicgases.
Acyl chlorides can also be prepared using certain
phosphorus chloride reagents such as phosphorus trichlorideor phosphorus pentachloride:
:R-COOH + PCl5 → R-COCl + POCl3 + HCl
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