Phthalic acid

• O-phthalic
• 1,2- benzenedicarboxylic acid

Monoclinic, colorless plates, needles or scales

Fixed

1.59 g · cm -3

191 ° C (closed capillary)

Decomposes on heating

7.8 hPa ( 191 ° C)

• PKS1 = 2.95
• PKa2 = 5.41

• Poorly in cold water ( 5.74 g · l-1 at 20 ° C)
• Soluble in hot water and ethanol

Attention

7900 mg · kg -1 ( LD50, rat, oral)

Template: Infobox chemical / molecular formula search available

Phthalic acid [ fta ː l ... ] is a chemical that counts in the chemistry of the carboxylic acids, more specifically the dicarboxylic acids. Usually, the ortho -phthalic acid is referred to as phthalic acid, terephthalic acid, in addition to the the greatest industrial importance. The quantitatively most of the phthalic acids is used for the production of synthetic resins or synthetic fibers. The salts and esters of phthalic acids are mentioned phthalates. The esters are described in more detail under phthalates.

Phthalic acid as a term includes the group of three benzene positional isomers that differ by the arrangement of the two carboxylic acid groups. Specifically, these are:

History

O -phthalic acid was discovered in 1836 by Auguste Laurent in the oxidation of 1,2,3,4- tetrachloro-1 ,2,3,4 -tetrahydronaphthalene with nitric acid, that bears the name of this hydrocarbon.

Production

O -phthalic acid has long been produced only by oxidation of naphthalene; Today, however, is mainly used o -xylene as raw material by far. As isophthalic acid is produced from m - xylene, and the terephthalic acid from p-xylene.

Properties

O-phthalic acid is a colorless, crystalline solid. In water, the acid is soluble to a limited extent.

It crystallizes in the monoclinic crystal system, space group C2 / c with lattice parameters a = 500 pm, b = 1420 pm, c = 960 pm, and β = 93.5 °. In the unit cell contains four formula units.

Use

O-phthalic acid is a raw material for the production of polyester resins. Here, the phthalic acid or its anhydride with the polyhydric alcohols generally, for example, glycerol, is esterified. By boiling down of polyunsaturated vegetable oils such as linseed oil with phthalic acid and polyhydric alcohols, alkyd resins are prepared by transesterification. Phthalic acid is also a starting material for the representation of many dyes, color pigments or plasticizers. Some of phthalic acid esters used as plasticizers are a health controversy ( endocrine disruptors ). About the intermediate phthalonitrile or phthalic the thermally very stable phthalocyanines can be prepared. From the phthalic anhydride can be reached by the Friedel -Crafts acylation of benzene to anthraquinone, may be prepared from the vat.