Phthalic acid

Phthalic acid
IUPAC name benzene-1,2-dicarboxylic acid
Other names benzene-1,2-dioic acid, phthalic acid, ortho-phthalic acid
Identifiers
CAS number	88-99-3 Y
PubChem	1017
EC number	201-873-2
Jmol-3D images	Image 1
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	191 - 230 °C[1]
Solubility in water	0.6 g / 100 mL [2][3]
Acidity (pKa)	2.98, 5.28[4]
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 (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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.^[5]

Production

Phthalic acid is produced by the catalytic oxidation of naphthalene directly to phthalic anhydride and a subsequent hydrolysis of the anhydride.^[5]

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 naphthalenic 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.

Reactions and uses

Phthalic acid crystals

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.^[6]

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)

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.

See also

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

References

1. ^ Several melting points are reported, for example: (i) 210-211° C with decomposition (Sigma-Aldrich on-line), (ii) 191 °C in a sealed tube (Ullmann's Encyclopedia of Industrial Chemistry), (iii) 230 °C with conversion to phthalic anhydride and water (J.T.Baker MSDS).
2. ^ http://hazard.com/msds/mf/baker/baker/files/p4270.htm
3. ^ http://actrav.itcilo.org/actrav-english/telearn/osh/ic/88993.htm
4. ^ Brown, H.C., et al., in Baude, E.A. and Nachod, F.C., Determination of Organic Structures by Physical Methods, Academic Press, New York, 1955.
5. ^ ^{a b} Peter M. Lorz, Friedrich K. Towae, Walter Enke, Rudolf Jäckh, Naresh Bhargava, Wolfgang Hillesheim “Phthalic Acid and Derivatives” in Ullmann's Encyclopedia of Industrial Chemistry, 2007, Wiley-VCH, Weinheim. doi:10.1002/14356007.a20_181.pub2
6. ^ Richard N. McDonald and Charles E. Reineke (1988), "trans-1,2-Dihydrophthalic Acid", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv6p0461 ; Coll. Vol. 6: 461 

• Merck Index, 9th ed, #7178

External links

• International Chemical Safety Card 0768

 This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press.