Peroxycarboxylic acids

General formula of a peroxycarboxylic acid (above) compared to a carboxylic acid (below). The peroxycarboxyl residue is marked in blue . R is an organyl radical (alkyl radical, aryl radical, alkylaryl radical, etc.).

When peroxycarboxylic acids - also known peracids - referred to representative of a group of materials of organic compounds containing a peroxycarboxylic (Peroxycarbonsäurengruppe) as the functional group contained. All peroxycarboxylic acids contain a free hydroperoxide group (HOO group) and can therefore be regarded as acyl hydroperoxides. Like most peroxides , the peroxycarboxylic acids are explosive in pure or highly concentrated form . The explosiveness decreases with increasing chain length. Short-chain aliphatic peroxycarboxylic acids are water-soluble up to ~ C ₆ , after which the water-insoluble ( lipophilic ) part of the molecule predominates . Aromatic peroxycarboxylic acids are more soluble in organic solvents than in water.

Manufacturing

Peroxycarboxylic acids are prepared from carboxylic acids and hydrogen peroxide ( reverse reaction equation 2 under reactions ). Above all, aromatic peroxycarboxylic acids are prepared from carboxylic acid chlorides and hydrogen peroxide in a basic medium.

m -chlorobenzoyl chloride + hydrogen peroxide → m -chloroperoxybenzoic acid

Peroxycarboxylic acids are also formed by the autoxidation of aldehydes .

Reactions

Peroxycarboxylic acids are usually unstable and are therefore only produced from the carboxylic acid and hydrogen peroxide during the reaction during syntheses ( in situ ). An exception is meta -chloroperbenzoic acid , which is crystalline and stable.

Peroxycarboxylic acids and alkenes can react to form epoxides at room temperature ( Prileschajew reaction ). In addition to the epoxide, a carboxylic acid is formed. Meta- chloroperbenzoic acid (MCPBA) is often used as the peroxycarboxylic acid . Other peroxycarboxylic acids that can be used for epoxidation are peroxyformic acid and peroxyacetic acid .

Formation of an epoxide from an alkene and a peroxycarboxylic acid.

Peroxycarboxylic acids serve as oxidizing agents , for example in Baeyer-Villiger oxidations .

Peroxycarboxylic acids are weak acids and as such enter into acid-base reactions . Their salts can be used for purification and isolation.

Peroxycarboxylic acid + water → carboxylic acid + hydrogen peroxide

literature

• Christian Caspari: The chemistry of organic peroxides with special consideration of safety aspects . April 26, 1998 ( PDF; 0.4 MB [accessed on March 21, 2007] thesis).

Individual evidence

1. ↑ Otto-Albrecht Neumüller (Ed.): Römpps Chemie-Lexikon. Volume 4: M-Pk. 8th revised and expanded edition. Franckh'sche Verlagshandlung, Stuttgart 1985, ISBN 3-440-04514-5 , p. 3068.