Phthalic anhydride

Phthalic anhydride
IUPAC name

2-benzofuran-1,3-dione [1]
Other names

Isobenzofuran-1,3-dione
Identifiers
CAS number 85-44-9 Y
RTECS number TI3150000
Jmol-3D images Image 1
Properties
Molecular formula C8H4O3
Molar mass 148.1 g/mol
Appearance white Flakes
Density 1.53 g/cm3, solid
Melting point

131 °C
Boiling point

295 °C subl.
Solubility in water 0.62 g/100g (20—25 °C);
19.0 g/100g (100 °C);
reacts slowly
Hazards
R-phrases R22, R37/38, R41, R42/43
S-phrases (S2), S23, S24/25, S26, S37/39, S46
NFPA 704
1
3
0
Flash point 152 °C
Related compounds
Related compounds Phthalic acid
Phthalimide
Phthalide
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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 2002, approximately 4.6 billion kilograms were produced.[1]

Contents

Synthesis and production

Phthalic anhydride was first reported in 1836 by Laurent. It is presently obtained by catalytic oxidation of ortho-xylene and naphthalene (Gibbs phthalic anhydride process):

C6H4(CH3)2 + 3 O2 → C6H4(CO)2O + 3 H2O
C10H8 + 4.5 O2 → C6H4(CO)2O + 2 H2O + 2 CO2

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 prepared from phthalic acid:[1]

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.[2] 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.[1] 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 \overrightarrow{\leftarrow} C6H4(CO2R)2 + H2O

The most important diester is bis(2-ethylhexyl) phthalate ("DEHP"), used in the manufacture of polyvinyl chloride.

Organic synthesis

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.[3] A related ring-opening reaction involves peroxides to give the useful peroxy acid:[4]

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.[5]

References

  1. ^ a b c 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
  2. ^ Noller, Carl R. (1965). Chemistry of Organic Compounds, 3rd ed.. Philadelphia: W. B. Saunders. pp. 602. 
  3. ^ Joseph Kenyon (1941), "d- and l-Octanol-2", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV1P0418 ; Coll. Vol. 1: 418 
  4. ^ George B. Payne (1973), "Monoperphthalic acid", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV5P0805 ; Coll. Vol. 5: 805 
  5. ^ L. A. Bigelow and H. H. Reynolds (1941), "Quinizarin", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV1P0476 ; Coll. Vol. 1: 476 

External links