Carboxylic acid anhydrides are the products of the dehydration of their molecules. These bio compounds are characterized by isomerism of radicals. When naming carboxylic acid anhydrides, historical nomenclature is most often used (for example, acetic anhydride , maleic anhydride, etc.). In the process of adding water-removing agents (usually phosphorus oxide) to carboxylic acids, their dehydration occurs, resulting in the formation of carboxylic acid anhydrides.
Acetic anhydride: preparation
The specified connection can be obtained in several ways. For its synthesis, phosphorus oxide, which is a very powerful dewatering agent, is most often used. There are also other methods for synthesizing this anhydride. For example, acetic anhydride can be obtained by the action of phosphate anhydride on acetate acid. During the cooling process, one particle of CH3CO1 is added dropwise to one particle of dehydrated and thoroughly dried acetate-acid sodium. The resulting mixture was heated moderately, and the synthesized acetic anhydride was distilled off in a sand bath, and then purified by distillation. As a result of this work, a liquid strongly smelling of acetate acid is obtained.
Acetic anhydride, as well as low molecular weight substances - liquids with a pungent odor, practically insoluble in water, are well soluble in many organic substances. It should be noted that higher carboxylic acid anhydrides (especially limiting ones) are odorless solids. Their boiling point is much higher compared to 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 anhydrides react with water, two molecules of the corresponding acid are obtained.
Amonolysis 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 .
Acetate anhydride is used as a dehydrogenating and acetylating agent in the production of acetylcellulose, vinyl acetate, medicines, dimethylacetamide, colorants, aromatic substances, etc. Acetaldehyde irritates the respiratory tract, eyes, and also causes skin burns.
Cellulose acetate is obtained due to the action of acetate anhydride on the cellulose in the presence of a catalyst (sulfate acid). With incomplete acetylation, cellulose mono- and diacetates are obtained. Cellulose di- and triacetates 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 pressed through special filters. Thin strips of the solution dry out and turn into threads, which are used to produce different types of synthetic fiber yarn.
For industrial purposes, other types of anhydrides are used. Maleic anhydride - a crystalline substance, readily soluble in water, as well as in acetone, melts at 52.85 ° C. Typically, this substance is obtained from maleic acid. It is used in the production process of pesticides, polyester and alkyd resins. Phthalic anhydride is obtained due to the oxidation of naphthalene. The latter is used for the synthesis of growth stimulants, insecticides, as well as some medications. Phthalic anhydride is a crystalline substance with a melting point of 128 ° C. The specified anhydride is used to obtain phenolphthalein (indicator and medication). This anhydride is used to make repellents (dimethyl phthalate).