Acyl halide
Carboxylic acid halides, also called Alkanoylhalogenide, are in the chemical compounds of a group of substances that are derived from carboxylic acids. Among them, the hydroxy group of the carboxylic acid is replaced by a halogen atom, so that a halocarbonyl results. The carbonyl halides most commonly used are the carboxylic acid chlorides.
Nomenclature
The designation can be done either as the acid halide, based on the acyl group, or a halocarbonyl. Examples:
- Acetic acid or acetyl fluoride or Fluorcarbonylmethan
- Benzoyl chloride or benzoyl chloride or Chlorcarbonylbenzol
- Formic acid chloride or chloroformate or Chlorocarbonyl is a hypothetical or under high pressure and very low temperatures existing substance. In normal conditions, it decomposes into CO and HCl. Much more resistant formyl H -COF.
Representation
Methods for the preparation of carboxylic acid chlorides from carboxylic acids are described under the heading of carboxylic acid chlorides.
The synthesis reactions shown therein also work to the corresponding fluoro- and bromo analogues. Carboxylic acid fluorides also obtained from carboxylic acid chlorides and potassium hydrogen elimination of potassium chloride and hydrogen chloride:
Carbonsäureiodide be prepared from carboxylic acid chlorides by reaction with hydrogen iodide and with elimination of hydrogen chloride:
Properties
Most low molecular weight carboxylic acid halides are colorless, pungent-smelling liquids, smoke in moist air because of hydrolysis to carboxylic acids and hydrogen halides. Compared to the respective carboxylic acid melting and boiling points are lower because no hydrogen bonds can form. All carbonyl halides are flammable. By the - I effect of the halogen atom, the carbon atom of the carbonyl group is more positively charged, thus significantly more reactive than the corresponding carboxylic acid.
Reactions
Hydrolysis
Carbonyl halides react with water to stormy, highly exothermic reaction to the respective carboxylic acid and the corresponding hydrogen halide:
For exact mechanism see also: addition-elimination mechanism.
Amide formation
Reaction with ammonia, the corresponding carboxylic acid amides can be prepared:
It is also a hydrogen halide 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 carbonyl halides have to be with a Lewis acid, aluminum trichloride here, previously enabled.
For more reactions, see: carboxylic acid chlorides.
Use
The carbonyl halides are the carbonyl compounds with the greatest reactivity. Therefore run many reactions that only under special conditions are possible starting from the pure carboxylic acid, much easier from. Examples of the use are representation of the carboxylic acid esters or the Friedel-Crafts acylation.
Safety
Since the carboxylic acid halides hydrolyze very light and generates heat, they must be stored as dry as possible. Escaping hydrogen halide acids irritate mucous membranes, eyes and skin. The reaction with lower alcohols usually runs similar stormy forming the ester and the hydrogen halide acid. All carbonyl halides are also flammable.