Catechol
Colorless crystals
Fixed
1.34 g · cm -3
105 ° C.
245 ° C.
20 Pa ( 20 ° C)
- Well in water (451 g · l-1 at 20 ° C)
- Soluble in many organic solvents and alkalis
Attention
Template: Infobox chemical / molecular formula search available
Catechol, 1,2- dihydroxybenzene, English: catechol ( short form of pyrocatechol ) - IUPAC 1,2- dihydroxybenzene or benzene -1 ,2 -diol called - is a divalent phenol, an aromatic alcohol. It has two adjacent to exploiting dividend in so-called ortho- position hydroxyl groups on a benzene ring.
Except catechol (1,2- dihydroxybenzene ), there are two more positionally isomeric forms, namely the resorcinol (1,3- dihydroxybenzene ) and hydroquinone (1,4- dihydroxybenzene ).
History and habitat
The trivial name of the chemical compound dates back to the Gerber - acacia ( Acacia catechu ). From their sap, which contains catechin, it was in 1839 by the chemist K. Reinsch by dry distillation, called Pyrolysis ( ancient name for pyrolysis), isolated for the first time. In addition, the names of catechol and pyrocatechol are common for catechol.
Catechol is used in tree resin and Beechwood.
Production and representation
Catechol can be illustrated with the aid of an alkali melt of o- chlorophenol or o -phenol sulfonic acid.
Likewise, an ether cleavage of guaiacol with hydrogen bromide is possible.
Properties
Catechol forms colorless crystals that are readily volatile with steam. In the air and when exposed to light, it is unstable and oxidized to 1,2- benzoquinone ( autoxidation ).
An aqueous solution, especially at pH values higher than 7, is brown in color. In neutral solution, the combination with iron (III ) chloride gives a green color. This reaction can serve to distinguish the dihydroxybenzenes include resorcinol is a violet color, hydroquinone, a blue color, which disappears after a short time when the hydroquinone is oxidized to p-benzoquinone by the iron (III ) chloride, does not show any color reaction. With lead (II ) acetate on the other hand forms a colorless precipitate. A blue-green color is the reaction of catechol with Vanadinschwefelsäure ( 1 part of ammonium vanadate on 100 parts of sulfuric acid ). Also, a blue-green color is the reaction with chloride of lime. Catechol is a strong reducing agent that Fehling's solution is able to reduce Benedict's reagent and ammoniacal silver nitrate solution.
Use
The uses of catechol are a family of techniques as a developer. To use it comes as anti-oxidant and disinfectant. In organic synthesis, it plays a role as raw material for dyes, perfumes and medicines and as a protecting group for carbonyl compounds.
The hydroborating agent is a catechol derivative of pyrocatechol. Methylations result guaiacol ( monomethyl ether ) and veratrole ( dimethyl ether ):
Natural Products
From the catechol and its methyl ethers of guaiacol and veratrole numerous natural products derived from this, including the famous vanillin. The aforementioned three basic compounds are formed by decarboxylation of the corresponding acids: eg Veratrole from veratric. Veratraldehyde is again shown from veratrole by Vilsmeier formylation.
Proof
For qualitative analytical detection arises in the bromination with potassium bromide and bromine the Tetrabromderivat with a melting point of 192 ° C.
Safety
The Dihydroxybenzenes irritate eyes, skin and respiratory tract. They are harmful in contact with skin and if swallowed. Catechol is toxic to aquatic organisms and therefore classified as dangerous for the environment in water hazard class 2.