Acid halides

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Organic and inorganic acid halides (from top to bottom): carboxylic acid halides, thiocarboxylic acid halides and organic sulfonic acid halide. Including sulfonic acid dihalide and phosphorus oxide halide. The functional group is marked in blue , X = F, Cl, Br, I. R is an organyl residue.

Acid halides are a group of substances in chemistry. A distinction is made between the derivatives of carboxylic acids ( carboxylic acid halides ) and sulfonic acids (sulfonic acid halides), which are included in organic chemistry , and the derivatives of inorganic oxygen acids .

Acid halides usually have a lower boiling point than the corresponding acids, they are often quite reactive and are usually quickly decomposed by water. However, the acid halides of long-chain fatty acids are solid at 20 ° C , while the acids are liquid.

Derivatives of carboxylic acids, thiocarboxylic acids and sulfonic acids

If a hydroxyl group in carboxylic acids, thiocarboxylic acids or sulfonic acids is replaced by a halogen atom, the result is carboxylic acid, thiocarboxylic acid or sulfonic acid halides. The carboxylic acid halides are particularly important. A distinction is made between carboxylic acid fluorides, carboxylic acid chlorides , carboxylic acid bromides and carboxylic acid iodides. Among the carboxylic acid halides, the carboxylic acid chlorides are particularly important as reactive starting materials or intermediates in organic syntheses , for example acetyl chloride or benzoyl chloride . Sulphonic acid halides (especially sulphonic acid chlorides) are used in organic synthesis in order to form a good leaving group ( mesylate , tosylate ) from a poor hydroxide leaving group during nucleophilic substitution .

Representation of the carboxylic acid halides

To prepare a carboxylic acid chloride, a carboxylic acid is reacted with thionyl chloride, phosphorus pentachloride , phosphorus oxychloride or phosphorus trichloride . The analogous carboxylic acid fluorides, bromides and iodides are obtained by reacting the carboxylic acid with thionyl halides SOX 2 (X = F, Br, I).

Derivatives of inorganic oxygen acids

If a hydroxyl radical is formally replaced by a halogen in inorganic oxo acids (examples: sulfuric acid, phosphoric acid, silicic acid), acid halides of these oxo acids result. Important inorganic acid halides are silicon tetrafluoride (tetrafluoride of silicic acid , SiF 4 ), sulfuryl chloride (the dichloride of sulfuric acid , SO 2 Cl 2 ), thionyl chloride (dichloride of sulfuric acid , SOCl 2 ), chlorosulfonic acid (monochloride of sulfuric acid, HSO 3 Cl), phosgene (Dichloride of carbonic acid , COCl 2 ), phosphorus oxychloride (trichloride of phosphoric acid, POCl 3 ), nitrosyl chloride (chloride of nitrous acid , NOCl), phosphorus tribromide (tribromide of phosphorous acid , PBr 3 ).

Representation of the halides of inorganic oxo acids

The inorganic acid halides are mostly produced by specific processes, e.g. B. Phosphorus tribromide is formed by the action of elemental bromine on red phosphorus.

Individual evidence

  1. ↑ Otto-Albrecht Neumüller (Ed.): Römpps Chemie-Lexikon. Volume 5: Pl-S. 8th revised and expanded edition. Franckh'sche Verlagshandlung, Stuttgart 1987, ISBN 3-440-04515-3 , pp. 3655-3656.
  2. ↑ a b c Brockhaus ABC Chemie , VEB FA Brockhaus Verlag Leipzig 1965, p. 1236.