Phthalic acid
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| Phthalic acid | |
|---|---|
 |
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| General | |
| Other names | Benzene-1,2- dicarboxylic acid |
| Molecular formula | C6H4(COOH)2 |
| SMILES | C1=CC=C(C(=C1) C(=O)O)C(=O)O |
| Molar mass | 166.14 g/mol |
| Appearance | white solid |
| CAS number | [88-99-3] |
| Properties | |
| Density and phase | 1.593 g/cm3, solid |
| Solubility in water | Slightly soluble |
| Solubility in ethanol | Soluble |
| Melting point | 210 °C decomp. |
| Acidity (pKa) | pKa1 = 2.92 pKa2 = 5.41 |
| Thermodynamic data | |
| Standard enthalpy of formation ΔfH°solid |
? kJ/mol |
| Standard enthalpy of combustion ΔcH°solid |
? kJ/mol |
| Standard molar entropy S°solid |
? J.K−1.mol−1 |
| Hazards | |
| EU classification | not listed |
| NFPA 704 |
1
0
1
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| Supplementary data page | |
| Structure and properties |
n, εr, etc. |
| Thermodynamic data |
Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Regulatory data | Flash point, RTECS number, etc. |
| Related compounds | |
| Related carboxylic acids | Isophthalic acid Terephthalic acid |
| Related compounds | Phthalic anhydride Phthalimide Phthalhydrazide Phthaloyl chloride Benzene-1,2- dicarboxaldehyde |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
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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.
Phthalic acid is used mainly in the form of the anhydride to produce other chemicals such as dyes, perfumes, saccharin, phthalates and many others.
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. It can be manufactured by oxidizing naphthalene tetrachloride (prepared from naphthalene, potassium, chlorate and hydrochloric acid) with nitric acid, or, better, by oxidizing the hydrocarbon with fuming sulfuric acid, using mercury or mercury(II) sulfate as a catalyst.
It forms white crystals, melting at 210 °C with decomposition into water and phthalic anhydride. Heating with an excess of lime produces benzene. The acid (and anhydride) are largely used in the color industry (see phenolphthalein).
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This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.
