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In organic chemistry, phthalic acid is an aromatic dicarboxylic acid, with Chemical formula and structure . 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 one of three isomers of benzenedicarboxylic acid, the others being isophthalic acid and terephthalic acid.
Phthalic acid was first obtained by France chemist Auguste Laurent in 1836 by oxidation naphthalene tetrachloride. Believing the resulting substance to be a naphthalene derivative, he named it "naphthalic acid".Auguste Laurent (1836) "Sur l'acide naphtalique et ses combinaisons" (On naphthalic acid and its compounds), Annales de Chimie et de Physique, 61 : 113-125. (Note: The empirical formulae of the compounds that were analyzed in this article are incorrect, in part because, during this period, chemists used incorrect atomic masses for carbon (6 instead of 12) and other elements.)Reprinted in German as: Auguste Laurent (1836) "Ueber Naphthalinsäure und ihre Verbindungen" (On naphthalenic acid and its compounds), Annalen der Pharmacie, 19 (1) : 38-50; for the preparation of phthalic acid, see page 41. After the Switzerland chemist Jean Charles Galissard de Marignac determined its correct formula,C. de Marignac (1841) "Ueber die Naphtalinsäure und ein bei ihrer Darstellung entstehendes flüchtiges Produkt" ("On naphthalinic acid and a volatile product that arises during its preparation"), Annalen der Chemie und Pharmacie, 38 (1) : 13-20. (Note: Again, Marignac's empirical formulae are wrong because chemists at this time used incorrect atomic masses.) Laurent gave it its present name.Auguste Laurent (1841) "Sur de nouvelles combinaisons nitrogénées de la naphtaline et sur les acides phtalique et nitrophtalique" (On new nitrogenous compounds of naphthalene, and on phthalic acid and nitrophthalic acid), Revue Scientifique et Industrielle, 6 : 76-99; on page 92, Laurent coins the name "acide phtalique" (phthalic acid) and admits that his earlier empirical formula for phthalic acid was wrong.Reprinted in German as: Auguste Laurent (1842) "Ueber neue stickstoffhaltige Verbindungen des Naphtalins, über Phtalinsäure und Nitrophtalinsäure" (On new nitrogenous compounds of naphthalene, on phthalic acid and nitrophthalic acid), Annalen der Chemie und Pharmacie, 41 (1) : 98-114; on page 108, Laurent coins the name "Phtalinsäure" (phthalic acid). 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.
Synthesis
Naphthalene, on oxidation with potassium permanganate or potassium dichromate, gives phthalic anhydride, which, through hydrolysis with hot water, gives phthalic acid. A more standard procedure is to oxidize napthalene with air, but this reaction proceeds explosively unless conditions are set up very accurately.
Uses
Phthalic acid in the form of phthalic anhydride is an important industrial chemical, used for making phthalates ( of phthalic acid) that are used as . However, phthalic anhydride is usually not made by dehydration of phthalic acid but from p-xylene or naphthalene.
Reactions
It is a dibasic acid, with p Kas of 2.89 and 5.51. The monopotassium salt, potassium hydrogen phthalate is a standard acid in analytical chemistry. Phthalate esters are typically 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.
Safety
The toxicity of phthalic acid is moderate with (mouse) of 550 mg/kg.
Biodegradation
The bacteria Pseudomonas sp. P1 degrades phthalic acid.
See also
External links
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