Acyl chloride

Carboxylic acid chlorides are the most important chemical compounds from the group of carboxylic acid halides, which are derived from carboxylic acids. Among them, the hydroxy group of the carboxylic acid is replaced by a chlorine atom, so that a chlorocarbonyl results. Depending on the nature of the organic radical one distinguishes, for example alkanoyl chlorides (R = alkyl ) and Aryloylchloriden (R = aryl, eg, phenyl ).

Nomenclature

Sometimes the terms " acid chloride " and " acid chloride " are also used interchangeably. This is not entirely correct, because although all carboxylic acid chlorides are also acid chlorides. However, not all of the acid chlorides, carboxylic acid chlorides, such as p- toluenesulfonyl chloride, although an acid chloride, but no carboxylic acid chloride.

The designation may be either an acid chloride, based on the names of the carboxylic acid or acyl group from the effected. Examples:

• Acetyl chloride or acetyl chloride, not to be confused with chloroacetic acid, ClCH2COOH
• Benzoyl chloride or benzoyl chloride, not to be confused with ortho -, meta- or para- chlorobenzoic acid
• Formic acid chloride or chloroformate is an existing hypothetical or under high pressure and very low temperatures substance. Under normal conditions it decomposes into hydrogen chloride and carbon monoxide.

Representation

Carboxylic acid chlorides are prepared by reaction of the corresponding carboxylic acids with thionyl chloride ( SOCl2 ), phosgene ( COCl2 ), phosphorus ( III ) chloride or phosphorus (V ) chloride synthesized:

Reaction with thionyl chloride ( SOCl2 ) with elimination of sulfur dioxide and hydrogen chloride:

The reaction with thionyl chloride has the advantage that all resulting materials, in addition to the desired carboxylic acid chloride are gaseous:

Reaction with phosgene ( COCl 2 ), with elimination of carbon dioxide and hydrogen chloride:

Reaction with phosphorus (III ) chloride with elimination of phosphonic acid:

Reaction with phosphorus (V ) chloride, phosphorus oxychloride and with elimination of hydrogen chloride:

The fluoro- and bromo analogues behave identically.

Properties

Most low molecular weight carboxylic acid chlorides are colorless, pungent-smelling liquids, smoke in moist air because of hydrolysis to carboxylic acids and hydrochloric acids. Compared to the respective carboxylic acid melting and boiling points are lower, since the carboxylic acid chlorides can not form hydrogen bonds. All carboxylic acid chlorides are flammable. By the - I effect of the chlorine atom to the carbon atom of the carbonyl group is more positively charged, thus significantly more reactive than the corresponding carboxylic acid.

Reactions

The carboxylic acid chlorides are carbonyl compounds with high reactivity. Therefore run many reactions that only under special conditions are possible starting from the pure carboxylic acid, from much easier with the corresponding carboxylic acid chloride.

Hydrolysis

Carbonyl chlorides react with water to stormy, highly exothermic reaction for the respective carboxylic acid and hydrogen chloride:

For exact mechanism see also: addition-elimination mechanism.

Amide formation

Reaction with ammonia, the corresponding carboxylic acid amides can be prepared:

It also hydrogen chloride is eliminated.

Ester formation

Reaction with alcohols to the corresponding carboxylic acid ester can be represented:

This reaction is irreversible, in contrast to that of carboxylic acids and alcohols.

Friedel-Crafts acylation of

By reaction with aromatics, benzene here, formed by a Friedel -Crafts acylation of aromatic ketones:

The aromatics have to be with a Lewis acid, aluminum trichloride here, previously enabled.

Formation of carboxylic

If, in the laboratory by the action of carboxylic acid chlorides on the alkali metal salts of carboxylic acids, in this case a sodium salt forth.

As a byproduct an alkali chloride, sodium chloride here.

Formation of ketones

A carboxylic acid chloride reacts with an organic cuprate, lithium dimethylcuprate herein to a ketone.

Byproducts of lithium chloride and copper ( I) chloride.

Safety

Since the carboxylic acid chlorides hydrolyze very light and generates heat, they must be stored as dry as possible. Escaping hydrogen chloride is irritating to mucous membranes, eyes and skin. The reaction with lower alcohols usually runs similar stormy forming the ester and hydrochloric acid.