- Acyl halide
An acyl halide (also known as an acid halide) is a
chemical compound derived from anoxoacid [http://goldbook.iupac.org/A00123.html] by replacing ahydroxyl group with ahalide group.GoldBookRef|title=acyl halides|url=http://goldbook.iupac.org/A00124.html]If the acid is a
carboxylic acid , the compound contains a –COXfunctional group , which consists of acarbonyl group singly bonded to ahalogen atom. The general formula for such an acyl halide can be written RCOX, where R may be, for example, analkyl group, CO is the carbonyl group, and X represents the halogen atom, such aschlorine .Acyl chloride s are the most commonly used acyl halides.The hydroxyl group of a
sulfonic acid may also be replaced by a halogen to produce the corresponding sulfonyl halide. In practical terms this is almost always chlorine to create asulfonyl chloride .Preparation
A common method for the synthesis of acyl halides in the laboratory is by reaction of
carboxylic acid s with reagents such asthionyl chloride orphosphorus pentachloride for acyl chlorides,phosphorus pentabromide for acyl bromides andcyanuric fluoride for acyl fluorides.Aromatic acyl chlorides can be prepared by
chloroformylation , a specific type ofFriedel-Crafts acylation usingformaldehyde as the reagent.Reactions
Acyl halides are rather reactive compounds often synthesized to be used as intermediates in the synthesis of other organic compounds. For example, an acyl halide can react with:
*water, to form acarboxylic acid
*analcohol to form anester
*anamine to form anamide
*anaromatic compound , using aLewis acid catalyst such as AlCl3, to form an aromaticketone . "See"Friedel-Crafts acylation .In the above reactions, HX (
hydrogen halide or hydrohalic acid) is also formed. For example, if the acyl halide is an acyl chloride, HCl (hydrogen chloride orhydrochloric acid ) is also formed.Multiple functional groups
A molecule can have more than one acyl halide functional group. For example, "adipoyl dichloride", usually simply called
adipoyl chloride , has two acyl chloridefunctional group s; see the structure at right. It is the dichloride (i.e., double chloride) of the 6-carbon dicarboxylic acidadipic acid . An important use of adipoyl chloride ispolymerization with an organic di-amino compound to form a polyamide callednylon or polymerization with certain other organic compounds to formpolyester s.Phosgene (carbonyl dichloride, Cl–CO–Cl) is a very toxic gas which may be thought of as the dichloride ofcarbonic acid (HO–CO–OH). Both chloride radicals in phosgene can undergo reactions analogous to the preceding reactions of acyl halides. Phosgene is used a reactant in the production ofpolycarbonate polymers, among other industrial applications.General hazards
Volatile acyl halides are
lachrymatory because they can react with water at the surface of the eye producing hydrohalic and organic acids irritating to the eye. Similar problems can result if one inhales acyl halide vapors. In general, acyl halides (even non-volatile compounds such astosyl chloride ) areirritant s to the eyes, skin andmucous membrane s.References
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