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.
Production Phthalic acid is produced by the catalytic
oxidation of naphthalene directly to phthalic anhydride and a subsequent hydrolysis of the
anhydride. 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 "naphthalic 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.
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. Safety
The toxicity of phthalic acid is low with LD50 of 550 mg/kg. However, many phthalate
esters have been implicated as endocrine disruptors. Biodegradation
The bacteria Pseudomonas sp. P1 degrades phthalic acid.
See also Isophthalic acid
Terephthalic acid Phthalate
Potassium hydrogen phthalate, a primary standard for acid-base titrations
Phthalic anhydride References
^ Several melting points are reported, for example: 210−211 °C with decomposition,
191 °C in a sealed tube, 230 °C with conversion to phthalic anhydride and water.
^ http:hazard.commfbakerp4270.htm ^ http:actrav.itcilo.orgtelearnic/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 ^ See:
Auguste Laurent "Sur l'acide naphtalique et ses combinaisons", Annales de Chimie et de
Physique, 61 : 113-125. and other elements.) Reprinted in German as: Auguste Laurent "Ueber
Naphthalinsäure und ihre Verbindungen", Annalen der Pharmacie, 19 : 38-50; for the preparation
of phthalic acid, see page 41.
^ C. de Marignac "Ueber die Naphtalinsäure und ein bei ihrer Darstellung entstehendes
flüchtiges Produkt", Annalen der Chemie und Pharmacie, 38 : 13-20.
^ See: Auguste Laurent "Sur de nouvelles combinaisons
nitrogénées de la naphtaline et sur les acides phtalique et nitrophtalique", Revue
Scientifique et Industrielle, 6 : 76-99; on page 92, Laurent coins the name "acide
phtalique" and admits that his earlier empirical formula for phthalic acid was wrong.
Reprinted in German as: Auguste Laurent "Ueber neue stickstoffhaltige Verbindungen des Naphtalins,
über Phtalinsäure und Nitrophtalinsäure", Annalen der Chemie und Pharmacie, 41 : 98-114;
on page 108, Laurent coins the name "Phtalinsäure".
^ Richard N. McDonald and Charles E. Reineke, "trans-1,2-Dihydrophthalic Acid", Org. Synth. ;
Coll. Vol. 6: 461 ^ Ishtiaq Ali, Muhammad. Microbial degradation
of polyvinyl chloride plastics. Quaid-i-Azam University. p. 47.
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.. Encyclopædia Britannica. Cambridge University
Press.