Phthalic acid

Phthalic acid

Names
Preferred IUPAC name Benzene-1,2-dicarboxylic acid
Other names 1,2-Benzenedioic acid Phthalic acid Benzene-1,2-dioic acid ortho-Phthalic acid
Identifiers
CAS Number	88-99-3 Y
3D model (Jmol)	Interactive image
ChEBI	CHEBI:29069 N
ChemSpider	992 N
ECHA InfoCard	100.001.703
EC Number	201-873-2
PubChem	1017
InChI InChI=1S/C8H6O4/c9-7(10)5-3-1-2-4-6(5)8(11)12/h1-4H,(H,9,10)(H,11,12) N Key: XNGIFLGASWRNHJ-UHFFFAOYSA-N N InChI=1/C8H6O4/c9-7(10)5-3-1-2-4-6(5)8(11)12/h1-4H,(H,9,10)(H,11,12) Key: XNGIFLGASWRNHJ-UHFFFAOYAX
SMILES C1=CC=C(C(=C1)C(=O)O)C(=O)O
Properties
Chemical formula	C8H6O4
Molar mass	166.14 g/mol
Appearance	white solid
Density	1.593 g/cm3, solid
Melting point	207 °C (405 °F; 480 K)
Solubility in water	0.6 g / 100 mL
Acidity (pKa)	2.89, 5.51
Magnetic susceptibility (χ)	-83.61·10−6 cm3/mol
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
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

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.

Phthalic acid is produced by the catalytic oxidation of naphthalene or ortho-xylene 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.

It is a dibasic acid, with pK_a's of 2.89 and 5.51. The monopotassium 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.