Phthalic acid
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| Names | |
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| IUPAC name
phthalic acid
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| Other names
benzene-1,2-dicarboxylic acid, ortho-phthalic acid
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| Identifiers | |
3D model (JSmol)
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| ECHA InfoCard | 100.001.703 |
| EC Number |
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PubChem CID
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CompTox Dashboard (EPA)
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| Properties | |
| C8H6O4 | |
| Molar mass | 166.14 g/mol |
| Appearance | white solid |
| Density | 1.593 g/cm3, solid |
| Melting point | 191 - 230 °C[1] |
| 0.6 g / 100 mL [2][3] | |
| Acidity (pKa) | 2.98, 5.28[4] |
| Hazards | |
| NFPA 704 (fire diamond) | |
| Related compounds | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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
It is a dibasic acid, with pKa'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.
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| 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
- Terephthalate
- Potassium hydrogen phthalate, a primary standard for acid-base titrations
- Phthalic anhydride
References
- ^ 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).
- ^ http://hazard.com/msds/mf/baker/baker/files/p4270.htm
- ^ http://actrav.itcilo.org/actrav-english/telearn/osh/ic/88993.htm
- ^ 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.
- ^ 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
- ^ Richard N. McDonald and Charles E. Reineke (1988). "trans-1,2-Dihydrophthalic Acid". Organic Syntheses; Collected Volumes, vol. 6, p. 461.
- Merck Index, 9th ed, #7178
External links
This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press. {{cite encyclopedia}}: Missing or empty |title= (help)
