Acetic anhydride: properties, production and application

Anhydrides of carboxylic acids are the products of the dehydration of their molecules. For these bio-compounds, isomerism of radicals is characteristic. When naming carboxylic anhydrides, the historical nomenclature (for example, acetic anhydride , maleic anhydride, etc.) is most often used. During the addition of dehydrating agents to carboxylic acids (usually phosphorus oxide), their dehydration occurs, resulting in the formation of carboxylic anhydrides.

Acetic anhydride: preparation

This compound can be washed in several ways. To synthesize it, phosphorus oxide is most often used, which is a very strong dehydrating agent. There are also other ways to synthesize this anhydride. For example, acetic anhydride can be produced by the action of phosphate anhydride on acetate. In the cooling process, one particle of CH3CO1 is added dropwise to one particle of dehydrated and thoroughly dried acetate-acid sodium. The resulting mixture is moderately heated, and the synthesized acetic anhydride is distilled off on a sand bath, after which it is purified by distillation. As a result of this work, a liquid that smells strongly of acetate is obtained.

Acetic anhydride, as well as low-molecular substances - liquids with an acute odor, practically insoluble in water, are readily soluble in many organic substances. It should be noted that the anhydrides of higher carboxylic acids (especially the limiting ones) are odorless solids. The temperature of their boiling is much higher than the corresponding carboxylic acids.

Acetic anhydride: chemical properties

This compound is often used to obtain many representatives of different classes of organic substances by organic synthesis methods. When the anhydrides react with water, two molecules of the corresponding acid are obtained.

Ammonolysis of anhydrides leads to the formation of amides and ammonium salts of the corresponding carboxylic acids. Alkolysis reactions are used to prepare esters from anhydrides .

Acetic anhydride is used as a dehydrogenating and acetylating agent in the production of acetylcellulose, vinyl acetate, medicaments, dimethylacetamide, dyes, aromatics, and the like. Acetaldehyde irritates the respiratory tract, eyes, and also causes skin burns.

Cellulose acetate is produced by the action of acetate anhydride on the cellulose in the presence of a catalyst (sulfate acid). In the case of incomplete acetylation, mono- and diacetates of cellulose are obtained. Di- and triacetates of cellulose are used in the production of acetate silk. To do this, they are dissolved in a mixture of acetone and ethanol (85:15) or in pure acetone. It turns out a viscous solution, which is forced through special filters. Thin strips of solution dry up and turn into threads, which are used to produce different types of yarn synthetic fibers.

For industrial purposes, other types of anhydrides are also used. Maleic anhydride, a crystalline substance that is highly soluble in water, and also in acetone, melts at 52.85 ° C. Typically, this substance is derived from maleic acid. It is used in the production of pesticides, polyester and alkyd resins. Phthalic anhydride is produced by oxidation of naphthalene. The latter is used for the synthesis of growth stimulants, insecticides, as well as some medicines. Phthalic anhydride is a crystalline substance with a melting point of 128 ° C. The said anhydride is used to produce phenolphthalein (indicator and medicament). This anhydride is used to make repellents (dimethyl phthalate).