Phthalic acid

Phthalic acid
Other names	Benzene-1,2- dicarboxylic acid
Identifiers
CAS number	88-99-3 Y
PubChem	1017
EC number	201-873-2
SMILES	C1=CC=C(C(=C1) C(=O)O)C(=O)O
Properties
Molecular formula	C8H6O4
Molar mass	166.14 g/mol
Appearance	white solid
Density	1.593 g/cm3, solid
Melting point	210 °C decomp.
Solubility in water	Slightly soluble
Hazards
NFPA 704	0 2 0
Related compounds
Related carboxylic acids	Isophthalic acid Terephthalic acid
Related compounds	Phthalic anhydride Phthalimide Phthalhydrazide Phthaloyl chloride Benzene-1,2- dicarboxaldehyde
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Phthalic acid (IUPAC systematic name: benzene-1,2-dicarboxylic acid) is an aromatic dicarboxylic acid, with formula C₆H₄(COOH)₂. It is an isomer of isophthalic acid and terephthalic acid.

Uses

Phthalic acid is used mainly in the form of the anhydride to produce other chemicals such as dyes, perfumes, saccharin, phthalates and many others.

History

Phthalic acid was obtained by French chemist Auguste Laurent in 1836 by oxidizing naphthalene tetrachloride, and, believing the resulting substance to be a naphthalene derivative, he named it naphthalenic acid. Swiss chemist Jean Charles Galissard de Marignac determined its formula and showed Laurent’s supposition to be incorrect, upon which Laurent gave it its present name. Manufacturing methods in the nineteenth century included oxidation of naphthalene tetrachloride (prepared from naphthalene, potassium chlorate and hydrochloric acid) with nitric acid, or, better, oxidation of the hydrocarbon with fuming sulfuric acid, using mercury or mercury(II) sulfate as a catalyst.

The catalytic oxidation of naphthalene directly to phthalic anhydride and a subsequent hydrolysis of the anhydride is one of the new production methods.

Chemistry

Phthalic acid crystals

It forms white crystals, melting at 210 °C with decomposition into water and phthalic anhydride. Heating with an excess of lime (calcium carbonate) produces benzene. The acid (and anhydride) are largely used in the color industry (see phenolphthalein).

Isomers

Phthalic acid is one of three isomers of benzenedicarboxylic acid, the others being isophthalic 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.

Phthalic acid	Isophthalic acid	Terephthalic acid
(ortho-phthalic acid)	(meta-phthalic acid)	(para-phthalic acid)

See also

• Isophthalic acid
• Terephthalic acid
• Phthalate
• Terephthalate
• Potassium hydrogen phthalate, a primary standard for acid-base titrations
• Phthalic anhydride

References

For more details, please, look at:

• Merck Index, 9th ed, #7178

• Ullmann's encyclopedia of industrial chemistry. 5th completely revised ed. Vol. A 26. VCH Verlagsgesellschaft, 1995.

• Lorz, P.M.; F.K. Towae, W. Enke, R. Jäckh, N. Bhargava (2002). "Phthalic acid and derivatives". Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH, Weinheim. 

External links

• International Chemical Safety Card 0768

This article incorporates text from the Encyclopædia Britannica, Eleventh Edition, a publication now in the public domain.