Isophthalic acid is widely used in the manufacture of paints and varnishes. Paintwork materials with its content have high technical characteristics. The main method of 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 salts and esters are called isophthalates.
In appearance, it is a solid, refractory white powder.
The empirical formula of isophthalic acid is: C 8 H 6 O 4 . The structural formula of this compound is shown in the figure below.
The properties
The main properties of this substance are as follows:
- molecular weight 166.14;
- melting point - 345-348 ° C;
- bulk density - 0.8 g / ml;
- aerosol flash point - 700 ° ;
- solubility: good in water and aqueous solutions of alkalis, poor in cold CH₃COOH, methanol, propanol and lower alcohols.
Isophthalic acid on contact irritates human skin, therefore, when working with it, safety measures must be observed.
Interaction with other compounds:
- when reacting with alkalis, forms salts;
- when heated with alcohols, esters are obtained;
- in reaction with thionyl chloride, carbonic acid dichloride and acetyl chloride, when heated to 130 ° C, isophthalic acid is converted to isophthaloyl chloride;
- in acetic acid at room temperature it is reduced with hydrogen in C 6 H 10 (COOH) 2 (cis-hexahydroisophthalic acid);
- nitrated with nitric acid at a temperature of 30 ° C (4 and 5-nitro derivatives are obtained) and sulfonated with fuming sulfuric acid at 200 ° C.
Preparation 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 occurs at a temperature of 100-150 ° C and at a pressure of 14-27 atmospheres. As catalysts, cobalt salts and acetaldehyde are used.
- In the oxidation of meta-xylene or m-toluic acid, with heating to 200 ° C, at a pressure of 40 atm. and in the presence of concentrated nitric acid.
- In the oxidative reaction of C 12 H 18 (1,3-diisopropylbenzene) with air. The reaction temperature is 120-220 ° C, the catalysts are cobalt and manganese salts.
- In the process of cleavage of the carboxyl group of trimellitic acid in an aqueous solution of sodium hydroxyl. The reaction temperature is 250 ° C.
The resulting product is purified by crystallization from acetic acid or from an aqueous solution of ethanol (in laboratory conditions). Since the production of C 8 H 6 O 4 takes place in corrosive environments, industrial equipment is made of a chemically resistant material - titanium.
Application
Isophthalic acid is mainly used for the manufacture of coatings (polyurethane, powder, alkyd), as well as polyester resins. Other areas of application are the production of materials such as:
- thermoplastic polymers;
- gelcoats - gel-like decorative protective coatings;
- water-based polyester resins;
- polyesters for glass reinforced plastics;
- hot-melamine enamels;
- production of plastic bottles and rubbers (as comonomer).
Paint coatings with isophthalic acid are characterized by high performance:
- good resistance to atmospheric factors;
- hardness;
- resistance to elevated temperatures, high limit of thermal deformation;
- corrosion and chemical resistance;
- stain resistance.
Enamels are used in the following industries:
- automotive industry;
- polygraphy;
- building materials;
- furniture manufacture;
- production of garden equipment;
- production of vending machines and others.