organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic matter, organic materials, i.e., matter in its various forms that contain ...

, phthalic acid is an

aromatic In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated system, conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugati ...

dicarboxylic acid, with

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

and

structure A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such as ...

. 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 In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the existence or possibili ...

of benzenedicarboxylic acid, the others being

isophthalic acid Isophthalic acid is an organic compound with the formula C6H4(CO2H)2. This colorless solid is an isomer of phthalic acid and terephthalic acid. The main industrial uses of purified isophthalic acid (PIA) are for the production of polyethylene ...

and terephthalic acid.

Production

Phthalic acid is produced by the catalytic oxidation of

naphthalene Naphthalene is an organic compound with formula . It is the simplest polycyclic aromatic hydrocarbon, and is a white Crystal, crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 Parts-per notation ...

or ''ortho-''xylene directly to phthalic anhydride and a subsequent hydrolysis of the anhydride. Phthalic acid was first obtained by French

chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a graduated scientist trained in the study of chemistry, or an officially enrolled student in the field. Chemists study the composition of ...

Auguste Laurent in 1836 by

oxidizing Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

naphthalene tetrachloride. Believing the resulting substance to be a naphthalene derivative, he named it "naphthalic acid". After the

Swiss Swiss most commonly refers to: * the adjectival form of Switzerland * Swiss people Swiss may also refer to: Places * Swiss, Missouri * Swiss, North Carolina * Swiss, West Virginia * Swiss, Wisconsin Other uses * Swiss Café, an old café located ...

chemist

Jean Charles Galissard de Marignac Jean Charles Galissard de Marignac (24 April 1817 – 15 April 1894) was a Swiss chemist whose work with atomic weights suggested the possibility of isotopes and the packing fraction of nuclei. His study of the rare earth elements led to ...

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 Mercury(II) sulfate, commonly called Mercury sulfate, mercuric sulfate, is the chemical compound Mercury (element), HgSulfur, SOxygen, O4. It is an odorless salt that forms white granules or crystalline powder. In water, it separates into an inso ...

as a catalyst.

Synthesis

Naphthalene, on oxidation with

potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4. It is a purplish-black crystalline salt, which dissolves in water as K+ and ions to give an intensely pink to purple solution. Potassium permanganate is widely us ...

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 (

ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

s of phthalic acid) that are used as plasticizers. However, phthalic anhydride is usually not made by dehydration of phthalic acid but from p-xylene or

Reactions

It is a dibasic acid, with p''K''_as of 2.89 and 5.51. The monopotassium salt, potassium hydrogen phthalate is a standard acid in

analytical chemistry Analytical skill, Analytical chemistry studies and uses instruments and methods to Separation process, separate, identify, and Quantification (science), quantify matter. In practice, separation, identification or quantification may constitute t ...

. 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.

References

* Merck Index, 9th ed, #7178

External links

International Chemical Safety Card 0768
{{Authority control Benzoic acids Dicarboxylic acids