2,4-Dihydroxybenzoic acid
β - resorcylic
White powder
Fixed
208-211 ° C
- 3.30 (COOH)
- 9.12 ( p- OH)
- 15.6 (ortho- OH)
- 8 g · l -1 ( 20 ° C)
- 70 g · l -1 ( 70 ° C)
- Soluble in ethanol and ether
Attention
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2,4-dihydroxybenzoic acid ( β - resorcylic acid ) is an aromatic compound which is derived both from the benzoic acid and of resorcinol (1,3- dihydroxybenzene ). The structure consists of a benzene ring with an attached carboxy (-COOH) and two hydroxy groups (-OH) as a substituent. It belongs to the group of dihydroxybenzoic acids.
Representation
2,4- dihydroxy can be prepared from resorcinol and potassium hydrogen carbonate by the Kolbe-Schmitt reaction.
Reactions and derivatives
Some alkyl esters of 2,4-dihydroxybenzoic acid, which acid and sulfuric acid as a catalyst can be prepared from the corresponding alcohols, which have been converted with thionyl chloride into the corresponding dialkyl sulfites showed antioxidant activity and anti- Parkinson activity in animal experiments.
Bromination of 2,4- dihydroxybenzoic acid with elemental bromine in glacial acetic acid results in first the 5- bromo-2 ,4 -dihydroxybenzoic acid, which can be converted by decarboxylation in the 4- bromoresorcinol. Upon further addition of bromine to 3,5- dibromo derivative forms. If the latter is treated with nitric acid, is produced by cleavage of the carboxyl group and a bromine atom, 4,6- dinitro -2- bromoresorcine.
The nitration also occurs initially at the 5 position. Is then nitrated with fuming nitric acid on, a second nitro group at the 3 position outsourced to. Upon further treatment with nitric acid produced styphnic. Both the mononitro - and dinitro derivative in can be removed by heating the carboxy group, there occur 4- nitroresorcinol and 2,4- dinitroresorcinol. 5-nitro- 2 ,4- dihydroxybenzoic acid may be reduced with tin and hydrochloric acid to the corresponding amino compound.
When introducing chlorine gas into a hot glacial acetic acid solution of 2,4-dihydroxybenzoic acid (melting point 224-225 ° C CAS 67828-44-8, ) or in excess of chlorine caused the 5-chloro- 3,5- dichloro derivative (mp 229 ° C). These 5- chloro-2 ,4 -dihydroxybenzoic acid with condensed resorcinols to Tetrahydroxybenzophenonen which react further ring closure to form the corresponding 7-chloro- 3 ,6- Dihydroxyxanthonen. If instead of the 5-chloro acid, the 5-nitro acid is used, the reaction stops at the ketone stand, ring closure takes place.
When reacted with methyl iodide in methanol, only the para- hydroxyl group is first methylated, it is formed of 2-hydroxy -4- methoxybenzoic acid. The methylation of the second hydroxy group is difficult. Can also be obtained with the p- monoethyl ethyl iodide.
During prolonged heating of an aqueous solution of the sodium salt of 2,4-dihydroxybenzoic acid partial isomerization to 2,6- dihydroxybenzoic acid takes place.
Further carboxylation of the 2,4-dihydroxybenzoic acid with ammonium bicarbonate results in the 2,4-dihydroxy -1 ,3- benzenedicarboxylic acid.
A close relative is the orsellinic, it differs specifically from the 2,4-dihydroxybenzoic acid by an added methyl group.