Phthalic acid was first obtained byFrenchchemistAuguste Laurent in 1836 byoxidizing naphthalene tetrachloride.[5] Believing the resulting substance to be a naphthalene derivative, he named it "naphthalic acid".[5][6][7] After theSwiss chemistJean Charles Galissard de Marignac determined its correct formula,[8] Laurent gave it its present name.[5][9][10] Manufacturing methods in the nineteenth century included oxidation of naphthalene tetrachloride with nitric acid, or, better, oxidation of the hydrocarbon withfuming sulfuric acid, using mercury ormercury(II) sulfate as a catalyst.
Naphthalene, on oxidation withpotassium permanganate orpotassium dichromate, gives phthalic anhydride,[citation needed] which, through hydrolysis with hot water, gives phthalic acid.[11] A more standard procedure is to oxidize napthalene with air, but this reaction proceeds explosively unless conditions are set up very accurately.[12]
Phthalic acid in the form ofphthalic anhydride is an important industrial chemical, used for makingphthalates (esters of phthalic acid) that are used asplasticizers. However, phthalic anhydride is usually not made by dehydration of phthalic acid but fromp-xylene ornaphthalene.
^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.
^Several melting points are reported, for example: (i) 480. K (NIST website), (ii) 210−211 °C with decomposition (Sigma-Aldrich on-line), (iii) 191 °C in a sealed tube (Ullmann's Encyclopedia of Industrial Chemistry), (iv) 230 °C with conversion to phthalic anhydride and water (J.T.Baker MSDS).
^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.
^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.)
