|Jmol-3D images||Image 1|
|Molar mass||148.1 g/mol|
|Density||1.53 g/cm3, solid|
295 °C subl.
|Solubility in water||0.62 g/100g (20—25 °C);
19.0 g/100g (100 °C);
|R-phrases||R22, R37/38, R41, R42/43|
|S-phrases||(S2), S23, S24/25, S26, S37/39, S46|
|Flash point||152 °C|
|Related compounds||Phthalic acid
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Phthalic anhydride is the organic compound with the formula C6H4(CO)2O. It is the anhydride of phthalic acid. This colourless solid is an important industrial chemical, especially for the large-scale production of plasticizers for plastics. In 2000, the world wide production volume of phthalic anhydride is estimated to be about 3 232 000 tonnes per year.
Synthesis and production
- C6H4(CH3)2 + 3 O2 → C6H4(CO)2O + 3 H2O
- C10H8 + 4.5 O2 → C6H4(CO)2O + 2 H2O + 2 CO2
The catalyst that is used for the oxidation of xylene is a modified vanadium pentoxide (V2O5). When separating the phthalic anhydride from byproducts such as o-xylene in water, or maleic anhydride, a series of “switch condensers” is required. Phthalic anhydride can also be prepared from phthalic acid:
Applications in industry and organic synthesis
Phthalic anhydride is a versatile intermediate in organic chemistry, in part because it is bifunctional and cheaply available. It undergoes hydrolysis and alcoholysis. Hydrolysis by hot water forms ortho-phthalic acid. This process is reversible: Phthalic anhydride re-forms upon heating the acid above 180 °C. Hydrolysis of anhydrides is not typically a reversible process. However, phthalic acid is easily dehydrated to form phthalic anhydride due to the creation of a thermodynamically favorable 5-membered ring.
Preparation of phthalate esters
As with other anhydrides, the alcoholysis reaction is the basis of the manufacture of phthalate esters, which are widely used (and controversial - see endocrine disruptor) plasticizers. In the 1980s, approximately 6.5×109 kg of these esters were produced annually, and the scale of production was increasing each year, all from phthalic anhydride. The process begins with the reaction of phthalic anhydride with alcohols, giving the monoesters:
- C6H4(CO)2O + ROH → C6H4(CO2H)CO2R
The second esterification is more difficult and requires removal of water:
- C6H4(CO2H)CO2R + ROH C6H4(CO2R)2 + H2O
Phthalic anhydride is a precursor to a variety of reagents useful in organic synthesis. Important derivatives include phthalimide and its many derivatives. Chiral alcohols form half-esters (see above), and these derivatives are often resolvable because they form diastereomeric salts with chiral amines such as brucine. A related ring-opening reaction involves peroxides to give the useful peroxy acid:
- C6H4(CO)2O + H2O2 → C6H4(CO3H)CO2H
Precursor to dyestuffs
Phthalic anhydride is widely used in industry for the production of certain dyes. A well-known application of this reactivity is the preparation of the anthroquinone dye quinizarin by reaction with para-chlorophenol followed by hydrolysis of the chloride.
Phthalic anhydride reacted with cellulose acetate forms cellulose acetate phthalate (CAP), a common enteric coating excipient that has also been shown to have antiviral activity. Phthalic anhydride is a degradation product of CAP.
- 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
- Noller, Carl R. (1965). Chemistry of Organic Compounds, 3rd ed. Philadelphia: W. B. Saunders. p. 602.
- Joseph Kenyon (1941), "d- and l-Octanol-2", Org. Synth.; Coll. Vol. 1: 418
- George B. Payne (1973), "Monoperphthalic acid", Org. Synth.; Coll. Vol. 5: 805
- L. A. Bigelow and H. H. Reynolds (1941), "Quinizarin", Org. Synth.; Coll. Vol. 1: 476
- Neurath AR. (2000). "Microbicide for prevention of sexually transmitted diseases using a pharmaceutical excipient.". AIDS Patient Care STDS. 14 (4): 215–9. doi:10.1089/108729100317830. PMC 538877. PMID 10806641.
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