Фталевая кислота

Описание

Phthalic acid is an aromatic dicarboxylic acid, with formula C₆H₄(CO₂H)₂. It is an isomer of isophthalic acid and terephthalic acid. Although phthalic acid is of modest commercial importance, the closely related derivative phthalic anhydride is a commodity chemical produced on a large scale.

Химические свойства

PHTHALIC ACID,C6H4(COOH)2, mp 208 °C (ortho), 330 °C (meta and iso), the ortho form sublimes and the meta and iso forms decompose with heat, sp gr 1.593 (ortho). Phthalic acid is very slightly soluble in H2O, soluble in alcohol, and slightly soluble in ether. The solid form is colorless, crystalline

Использование

It is a dibasic acid, with pKa's of 2.89 and 5.51. The mono potassium salt, potassium hydrogen phthalate is a standard acid in analytical chemistry. Typically phthalate esters are prepared from the widely available phthalic anhydride. Reduction of phthalic acid with sodium amalgam in the presence of water gives the 1,3- cyclohexadiene derivative.

Методы производства

Phthalic acid is produced by the catalytic oxidation of naphthalene directly to phthalic anhydride and a subsequent hydrolysis of the anhydride.
Phthalic acid was first obtained by French chemist Auguste Laurent in 1836 by oxidizing naphthalene tetrachloride. Believing the resulting substance to be a naphthalene derivative, he named it "naphthalic acid". After the Swiss chemist Jean Charles Galissard de Marignac determined its correct formula, Laurent gave it its present name. Manufacturing methods in the nineteenth century included oxidation of naphthalene tetrachloride with nitric acid, or, better, oxidation of the hydrocarbon with fuming sulfuric acid, using mercury or mercury(II) sulfate as a catalyst.

Определение

phthalic acid: colourlesscrystalline dicarboxylic acid,C₆H₄(COOH)₂; r.d. 1.6; m.p. 207°C.The two –COOH groups are substitutedon adjacent carbon atoms ofthe ring, the technical name beingbenzene-1,2-dicarboxylic acid. Theacid is made from phthalic anhydride(benzene-1,2-dicarboxylic anhydride,C₈H₄O₃), which is made by the catalyticoxidation of naphthalene. Theanhydride is used in making plasticizersand polyester resins.

Общее описание

White crystals or fine white powder.

Реакции воздуха и воды

Insoluble in water.

Профиль реактивности

Phthalic acid is a carboxylic acid. Phthalic acid is sensitive to exposure to extreme heat. Phthalic acid reacts violently with nitric acid. Phthalic acid is incompatible with sodium nitrite. Phthalic acid is also incompatible with oxidizers. .

Пожароопасность

Phthalic acid is combustible.

Профиль безопасности

Moderately toxic by ingestion and intraperitoneal routes. A skin and mucous membrane irritant. Combustible when heated. In the form of dust (anhydride) it can explode. Mixtures with sodmm nitrite explode when heated. Violent reaction with HNO3. When heated to decomposition it emits acrid smoke and irritating fumes. Used in synthesis of dyes and dyestuffs, in medcines and perfumes.

Безопасность

The toxicity of phthalic acid is low with LD₅₀ (mouse) of 550 mg/kg. However, many phthalate esters have been implicated as endocrine disruptors.

Методы очистки

Crystallise phthalic acid from water. [Beilstein 9 IV 3167.]