Isophthalic acid is widely used in the production of paints and varnishes. Coating materials with its content have high technical characteristics. The main method for obtaining this substance in the chemical industry is the oxidation of m-xylene in the presence of catalysts.
Description
Isophthalic acid is an organic compound that belongs to the class of carboxylic acids. It has in its composition 2 carboxyl groups -COOH, that is, it is a dicarboxylic acid. Another name for this substance is 1,3-benzenedicarboxylic acid. Its s alts and esters are called isophthalates.
In appearance, it is a hard, refractory white powder.
Empirical formula for isophthalic acid: C8H6O4. The structural formula of this compound is shown in the figure below.
Properties
The main properties of this substance are as follows:
- molecular weight – 166, 14;
- melting point - 345-348 °C;
- bulkdensity – 0.8 g/ml;
- aerosol flash point - 700 °С;
- solubility: good in water and aqueous alkali solutions, poor in cold CH₃COOH, methanol, propanol and lower alcohols.
Isophthalic acid irritates human skin upon contact, so safety precautions must be observed when working with it.
Interaction with other compounds:
- forms s alts when reacting with alkalis;
- when heated with alcohols, esters are obtained;
- reacts with thionyl chloride, carbonic acid dichloride and acetyl chloride when heated to 130 oC converts isophthalic acid to isophthaloyl chloride;
- in acetic acid at room temperature it is reduced by hydrogen to C6H10(COOH)2(cis-hexahydroisophthalic acid);
- nitrated with nitric acid at 30°C (4 and 5-nitro derivatives are obtained) and sulfonated with fuming sulfuric acid at 200°C.
Production of isophthalic acid
The synthesis of this compound in the chemical industry is carried out in several ways:
- In the oxidative reaction of metaxylene with air involving acetic acid. The process takes place at a temperature of 100-150 °C and at a pressure of 14-27 atmospheres. Cob alt s alts and acetaldehyde are used as catalysts.
- When oxidizing meta-xylene or m-toluic acid, heated to 200 °C, at a pressure of 40 atm. and in the presence of concentrated nitric acid.
- In the oxidative reaction of C12H18 (1, 3-diisopropylbenzene) with air. Reaction temperature 120-220°С, catalysts - s alts of cob alt and manganese.
- In the process of splitting off the carboxyl group of trimellitic acid in an aqueous solution of sodium hydroxyl. The reaction temperature is 250 °С.
The resulting product is purified by crystallization from acetic acid or from an aqueous solution of ethanol (in laboratory conditions). Since the production of C8H6O4 takes place in corrosive environments, industrial equipment is made of chemically resistant material - titanium.
Application
Isophthalic acid is used mainly for the manufacture of paint coatings (polyurethane, powder, alkyd), as well as polyester resins. Other applications are the production of materials such as:
- thermoplastic polymers;
- gelcoats - gel-like decorative and protective coatings;
- water-based polyester resins;
- polyesters for GRP;
- melamine stoving enamels;
- manufacture of plastic bottles and rubber (as comonomer).
Isophthalic acid paints are high performance:
- good weather resistance;
- hardness;
- high temperature resistance, high thermal deformation limit;
- corrosive and chemicaldurability;
- stain resistant.
Enamels are used in the following industries:
- automotive industry;
- printing;
- building materials;
- furniture manufacturing;
- manufacture of garden equipment;
- production of vending machines and others.
