Chemical Properties
White to light yellow crystal powder. 3-Hydroxybenzoic
acid does not undergo decarboxylation at elevated temperature and is stable up to 300℃. This is
in contrast to 2- and 4-hydroxybenzoic acids.
Electrophilic substitution (e.g., nitration, halogenation, sulfonation) occurs ortho or para to the
hydroxyl group. Thus, nitration with 62 % aqueous nitric acid gives 2-nitro-3-hydroxybenzoic
acid as the main product, along with 4-nitro- and
6-nitro-3-hydroxybenzoic acids.
Uses
3-Hydroxybenzoic acid is used as an intermediate in the manufacture of germicides, plasticizers, preservatives, light stabiliziers, petroleum additives, pharmaceuticals, and plasticizer. It can also be used for the synthesis of azo dyes and herbicide fomesafen.
Definition
ChEBI: 3-hydroxybenzoic acid is a monohydroxybenzoic acid that is benzoic acid substituted by a hydroxy group at position 3. It has been isolated from Taxus baccata. It is used as an intermediate in the synthesis of plasticisers, resins, pharmaceuticals, etc. It has a role as a bacterial metabolite and a plant metabolite. It derives from a benzoic acid. It is a conjugate acid of a 3-hydroxybenzoate.
Application
3-Hydroxybenzoic acid is used in perfumery. It is an important raw material and intermediate used in organic synthesis, pharmaceuticals agrochemicals and dyestuff fields.
Preparation
3-Hydroxybenzoic acid is synthesized from benzoic acid by sulfonation, alkali melting and hydrolysis.
122kg of benzoic acid was put into the reactor, and 100kg of oleum was added under stirring. The temperature was raised to about 100 °C, and the reaction was carried out for 2h to obtain Sodium 3-sulfobenzoate. Then the sulfonated liquid was transferred to an alkali melting pot, 45 kg of solid sodium hydroxide was added, the temperature was raised to melting, and reacted for 4 to 5 hours to obtain sodium m-carboxyphenate, and diluted sulfuric acid was added for acid hydrolysis. Cool and crystallize, filter out sodium sulfate, and decolorize the filter cake with activated carbon to obtain 3-Hydroxybenzoic acid.
Reactions
m-Hydroxybenzoic Acid, of the three hydroxybenzoic acids, the metaisomer is of least commercial importance. Unlike salicylic acid, m-hydroxybenzoic acid does not undergo the Friedel-Crafts reaction. It can be converted in 80% yield to m-aminophenol by the Schmidt reaction, which involves treating the acid with hydrazoic acid in trichloroethylene in the presence of sulfuric acid at 40 °C.
Purification Methods
Crystallise the hydroxyacid from absolute EtOH. [Beilstein 10 IV 315.]
