important representative polycarboxylic aromatic compounds are phthalic acid derivatives represented by certain isomers - ortho-isomer (directly, phthalic acid), meta-isomer (isophthalic) and para-isomer (terephthalic).All substances in this group are extremely widely used in various industries.
Terephthalic acid - pure colorless crystalline powder obtained in the reaction liquid phase oxidation of para-xylene in the presence of cobalt salt is a catalyst.The interaction of the substance with a variety of alcohols leads to the formation of chemical compounds the ester group.The most practical use is dimethyl terephthalate.
Terephthalic acid is also applicable for the synthesis of polyethylene terephthalate (PET), - a transparent heat-resistant polymer obtained by the polycondensation reaction of the substance with ethylene glycol.Then he produced from plastic bottles, polyester fibers terilenovoy Group, better known under the name "polyester", as well as a variety of packaging containers for the food industry, electronic components and various equipment.
According to their chemical properties similar to terephthalic acid monocarboxylic compound.She on heating or under the influence of so-called dehydrating substances readily forms salts, esters, complex molecular structure, anhydrides, amides, such as one or two carboxyl groups.Terephthalic acid also reacts esterification are formed as a result of which the mono- and diesters.Upon heating of the crystal to a temperature not less than two hundred degrees observed decarboxylation to give compounds containing the minimal number of carboxyl groups.However, electrophilic substitution reaction to deactivate the ring start to proceed with great difficulty.
Phthalic acid naturally found in green pigment of plants and poppy seed pods.Of its derivatives are most important compounds dibutyl ether and dimethyl phthalate, which are used as plasticizers of cellulose products, vinyl polymers and rubbers.Also, dimethyl, diethyl and dibutyl phthalate are essential components of various repellents.
Isophthalic acid is widely used in the manufacture of unsaturated polyester resins.Since isophthalates are excellent plasticizers.However, the greatest application of benzenepolycarboxylic group of compounds has yet terephthalic acid, which is used for the synthesis of important substances for the industry as polyethylene terephthalate and dimethyl terephthalate.They are used for the manufacture of a variety of mechanisms belts, ropes, conveyor belts, fishing nets, sails, rigging, trawls, petrol and nefteustoychivyh hoses, fasteners "lightning", strings of tennis rackets, and much more.In addition, the smooth textile fibers, in the manufacture of the substance is used, made jerseys, various fabrics (crepe, tweed, satin, etc.), Curtains products, raincoat, umbrella and costume materials, shirts, socks, baby clothesetc.
In conclusion, it should be noted that all the acid benzenepolycarboxylic series are extremely aggressive and toxic substances.Therefore, it is always attached to the Material Safety Data Sheet, which lists all the properties and characteristics of the compound, as well as the procedure and rules for working with them.
