Phthalic acid

Description

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.

Chemical properties

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

The Uses of Phthalic acid

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.

The Uses of Phthalic acid

Phthalic Acid (Phenyl-13C6, D4) is labelled Phthalic Acid (P384480) which is an organic reagent used to synthesize phthalates.

What are the applications of Application

Phthalic acid is an ortho-carboxylic acid benzoic acid derivative

Definition

ChEBI: A benzenedicarboxylic acid cosisting of two carboxy groups at ortho positions.

Definition

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.

Production Methods

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.

Synthesis Reference(s)

The Journal of Organic Chemistry, 30, p. 2414, 1965 DOI: 10.1021/jo01018a074

General Description

White crystals or fine white powder.

Air & Water Reactions

Insoluble in water.

Reactivity Profile

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. .

Fire Hazard

Phthalic acid is combustible.

Flammability and Explosibility

Not classified

Safety Profile

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.

Safety

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

Purification Methods

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

Isomers

Phthalic acid is one of three isomers of benzene dicarboxylic acid, the others being iso phthalic acid and terephthalic acid. Sometimes the term "phthalic acids" is used to refer to this family of isomers, but in the singular, "phthalic acid", refers exclusively to the ortho- isomer.