Phthalic anhydride

Chembox new
Name = Phthalic anhydride
ImageFile = Phthalic anhydride.png ImageSize = 100px
ImageName = Phthalic anhydride
ImageFile1 = Phthalic anhydride-3d.png ImageSize1 = 150px
IUPACName = 1,2-benzenedicarboxylic anhydride
OtherNames = Isobenzofuran-1,3-dione
Section1 = Chembox Identifiers
SMILES = C1=CC=C2C(=C1)C(=O)OC2=O
CASNo = 85-44-9
RTECS = TI3150000
Section2 = Chembox Properties
Formula = C₈H₄O₃
MolarMass = 148.1 g/mol
Appearance = white Flakes
Density = 1.53 g/cm³, solid
Solubility = 0.62 g/100g reacts slowly
MeltingPt = 131 °C
BoilingPt = 295 °C "subl."
Section3 = Chembox Structure
CrystalStruct =
Dipole =
Section7 = Chembox Hazards
EUClass =
RPhrases = R22, R37/38, R41, R42/43
SPhrases = S2, S23, S24/25, S26, S37/39, S46
FlashPt = 152 °C
Section8 = Chembox Related
OtherCpds = Phthalic acid
Phthalimide

Phthalic anhydride is the organic compound with the formula C₆H₄(CO)₂O. This anhydride of phthalic acid, a colourless solid, is an important industrial chemical, especially for the large-scale production of plasticizers.

ynthesis 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 + 2CO₂When separating the phthalic anhydride from byproducts such as o-xylene in water, or maleic anhydride, a series of switch condensers is required.

Applications in industry and organic synthesis

Phthalic anhydride is a versatile intermediate in organic chemistry, in part because it is bifunctional and cheaply available. Most characteristically, 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.cite book
last = Noller
first = Carl R.
title = Chemistry of Organic Compounds, 3rd ed.
publisher = W. B. Saunders
year = 1965
location = Philadelphia
pages = 602 ]

Preparation of phthalate esters

The alcoholysis reaction is the basis of the manufacture of phthalate esters, which are widely used plasticizers. [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, Wiley-VCH: Weinheim, 2002.] 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 gives the mixed esters::C₆H₄(CO)₂O + ROH → C₆H₄(CO₂H)CO₂RThe second esterification is more difficult and requires removal of water::C₆H₄(CO₂H)CO₂R + ROH $overrightarrow\{leftarrow\}$ C₆H₄(CO₂R)₂ + H₂OThe 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. [OrgSynth | author = Joseph Kenyon | title = "d"- and "l"-Octanol-2| collvol = 1 | collvolpages = 418| year = 1941 | prep = CV1P0418] A related ring-opening reaction involves peroxides to give the useful peroxy acid: [OrgSynth | author = George B. Payne | title = Monoperphthalic acid| collvol = 5 | collvolpages = 805| year = 1973 | prep = CV5P0805] :C₆H₄(CO)₂O + H₂O₂ → C₆H₄(CO₃H)CO₂H

When separating the phthalic anhydride from byproducts such as o-xylene in water, or maleic anhydride, a series of switch condensers is required, rather than a complicated setup of distillation columns that never converge in many industrial process simulation programs such as AspenTech.

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. [OrgSynth | author = L. A. Bigelow and H. H. Reynolds | title = Quinizarin | collvol = 1 | collvolpages = 476| year = 1941 | prep = CV1P0476]

References

External links

* [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc03/icsc0315.htm International Chemical Safety Card 0315]
* [http://www.cdc.gov/niosh/npg/npgd0512.html NIOSH Pocket Guide to Chemical Hazards]