Maleic anhydride

Maleic anhydride^[1]

Names
IUPAC name Furan-2,5-dione
Other names cis-Butenedioic anhydride; 2,5-Furanedione; Maleic acid anhydride; Toxilic anhydride
Identifiers
CAS Registry Number	108-31-6 Y
ChEBI	CHEBI:474859 N
ChEMBL	ChEMBL374159 Y
ChemSpider	7635 Y
EC-number	203-571-6
InChI InChI=1S/C4H2O3/c5-3-1-2-4(6)7-3/h1-2H Y Key: FPYJFEHAWHCUMM-UHFFFAOYSA-N Y InChI=1/C4H2O3/c5-3-1-2-4(6)7-3/h1-2H Key: FPYJFEHAWHCUMM-UHFFFAOYAP
Jmol-3D images	Image
PubChem	7923
RTECS number	UE5950000
SMILES C1=CC(=O)OC1=O
UNII	V5877ZJZ25 Y
Properties
Molecular formula	C4H2O3
Molar mass	98.06 g·mol−1
Appearance	White crystals or needles[2]
Odor	irritating, choking[2]
Density	1.48 g/cm3
Melting point	52.8 °C (127.0 °F; 325.9 K)
Boiling point	202 °C (396 °F; 475 K)
Solubility in water	Reacts
Vapor pressure	0.2 mmHg (20°C)[2]
Hazards
MSDS	MSDS at J. T. Baker
EU classification	Corrosive (C)
R-phrases	R22, R34, R42/43
S-phrases	(S2), S22, S26, S36/37/39, S45
NFPA 704	1 3 1
Flash point	102 °C (216 °F; 375 K)
Explosive limits	1.4%-7.1%[2]
LD50 (Median lethal dose)	465 mg/kg (oral, mouse) 850 mg/kg (oral, rat) 875 mg/kg (oral, rabbit) 390 mg/kg (oral, guinea pig) 400 mg/kg (oral, rat)[3]
US health exposure limits (NIOSH):
PEL (Permissible)	TWA 1 mg/m3 (0.25 ppm)[2]
REL (Recommended)	TWA 1 mg/m3 (0.25 ppm)[2]
IDLH (Immediate danger)	10 mg/m3[2]
Related compounds
Related acid anhydrides	Succinic anhydride
Related compounds	Maleic acid
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
N verify (what is: Y/N?)
Infobox references

Maleic anhydride is an organic compound with the formula C₂H₂(CO)₂O. It is the acid anhydride of maleic acid. It is a colorless or white solid with an acrid odor. It is produced industrially on a large scale for applications in coatings and polymers.^[4]

Production

Maleic anhydride was traditionally produced by the oxidation of benzene or other aromatic compounds. As of 2006, only a few smaller plants continue to use benzene. Instead, most maleic anhydride is produced by vapor-phase oxidation of n-butane. The overall process converts the methyl groups to carboxylate and dehydrogenates the backbone. The selectivity of the process reflects the robustness of maleic anhydride, with its conjugated double-bond system.

In both cases, benzene and butane are fed into a stream of hot air, and the mixture is passed through a catalyst bed at high temperature. The ratio of air to hydrocarbon is controlled to prevent the mixture from igniting. Vanadium pentoxide and molybdenum trioxide are the catalysts used for the benzene route, whereas vanadyl phosphate is used for the butane route.^[4]

C₄H₁₀ + 3.5 O₂ → C₂H₂C₂O₃ + 4 H₂O ∆H = -1236 kJ/mol

The main competing process entails full combustion of the butane, a conversion that is twice as exothermic as the partial oxidation.

Industrial production of maleic anhydride is achieved by integration of following unit processes: catalyst packed bed reactor, adsorption tower, maleic acid reactor, distillation column. The reactant stream of n-butane and air mixture enters the packed bed reactor at a temperature of 120-150 °C and a pressure of 2-3 atm. The product stream is then sent to a packed bed adsorption column, where the condensable maleic anhydride reacts with the water stream to give maleic acid and the non-condensable are sent for fuel gases treatment. The condensable stream from adsorption tower is sent to a maleic acid reactor, where maleic acid is again converted back to the anhydride. This product stream from reactor is sent to distillation column to obtain pure maleic anhydride as product.

Reactions

The chemistry of maleic anhydride is very rich, reflecting its ready availability and bifunctional reactivity. It hydrolyzes, producing maleic acid, cis-HOOC–CH=CH–COOH. With alcohols, the half-ester is generated, e.g., cis-HOOC–CH=CH–COOCH₃.

Maleic anhydride is a classic substrate for Diels-Alder reactions.^[5] It was used for work in 1928 on the reaction between maleic anhydride and 1,3-butadiene that Otto Paul Hermann Diels and Kurt Alder were awarded the Nobel prize in 1950. It is through this reaction that maleic anhydride converted to many pesticides and pharmaceuticals.

In 1979 a patent was granted to Lever Brothers for the Michael reaction of maleic anhydride with active methylene or methine compounds such as malonate or acetoacetate esters in the presence of sodium acetate catalyst. These intermediates were subsequently used for the generation of the Krebs cycle intermediates aconitic and isocitric acids.^[6]

Maleic anhydride dimerizes in a photochemical reaction to form cyclobutane tetracarboxylic dianhydride (CBTA). This compound is used in the production of polyimides and as an alignment film for liquid crystal displays.^[7]

It is also a ligand for low-valent metal complexes, examples being Pt(PPh₃)₂(MA) and Fe(CO)₄(MA).

Uses

Around 50% of world maleic anhydride output is used in the manufacture of unsaturated polyester resins (UPR). Chopped glass fibers are added to UPR to produce fibreglass reinforced plastics which are used in a wide range of applications such as pleasure boats, bathroom fixtures, automobiles, tanks and pipes. However, the UPR market reflects general economic conditions as it is tied to the construction, automobile and marine industries.

The production of 1,4-butandiol (BDO) is also having an impact on the maleic anhydride market. BDO is one of the world’s fastest growing chemicals used in the production of thermoplastic polyurethanes, elastane/Spandex fibers, polybutylene terephthalate (PBT) resins and many other products. However, BDO is made from a crude maleic anhydride which is not traded and only used for this application.

Another market for maleic anhydride is lubricating oil additives, which are used in gasoline and diesel engine crankcase oils as dispersants and corrosion inhibitors. Changes in lubricant specifications and more efficient engines have had a negative effect on the demand for lubricating oil additives, giving flat growth prospects for maleic anhydride in this application.

There are a number of smaller applications for maleic anhydride. The food industry uses maleic anhydride in artificial sweeteners and flavour enhancements. Personal care products consuming maleic anhydride include hair sprays, adhesives and floor polishes. Maleic anhydride is also used in water treatment chemicals, detergents, insecticides and fungicides, pharmaceuticals and copolymers.

Major producers

Source: Kirk & Othmer

Solid State Chemicals, Ltd. started production of solid maleic anhydride pastilles in the USA in 2014.

World Maleic Anhydride Capacity By Region
Data in: kilotonnes per annum

Source: Kirk & Othmer

Packing and transport

Liquid maleic anhydride is available in road tankers and/or tank-containers which are made of stainless steel, which are insulated and provided with heating systems to maintain the temperature of 65-75 °C. Tank cars must be approved for the transport of molten maleic anhydride.

Liquid/molten maleic anhydride is a dangerous material in accordance with RID/ADR.

Solid maleic anhydride pastilles are transported by transport trucks. Packaging is generally in 25kg polyethylene bags.

Storage

• Requirements for storage buildings
  • Local exhaust systems to take vapours away from the places of emission, and general ventilation in rooms.
  • Protection against static charges.
  • Impervious floor which makes it possible to collect the spilled material and which prevents its entry to the sewage system.
  • Storage rooms should be cool and dry.

• Storage conditions
  • Keep ignition sources away - do not smoke. Product dust may form explosive air-dust mixtures.
  • Keep humidity away from storage rooms.
  • Keep containers tightly closed. Store them in cool, dry and well ventilated places.
  • Tanks / containers must be properly marked.
  • Hand-operated / portable fire-fighting equipment should be available in storage rooms.
  • Neutral gas blanketing is required inside storage tanks.

Effects on human health and the environment

This compound also poses relatively low-risk environmental hazards, an important feature for those applications. Exposure to maleic anhydride may cause respiratory tract, eye irritation, skin irritation and respiratory irritation. Maleic anhydride is a skin and respiratory sensitizer.^[8]

Maleic anhydride is a low hazard profile chemical. Maleic anhydride rapidly hydrolyzes to form maleic acid in the presence of water and hence environmental exposures to maleic anhydride are not expected to occur. Maleic anhydride and maleic acid are biodegraded under aerobic conditions in sewage sludge and in soil and water as well.

Food starch for use in night markets sold from a supplier in Tainan city, Taiwan, were found to contain maleic anhydride in December 2013. The supplier was investigated regarding the 300 tons of tainted starch; an earlier inspection in November had found 32 tons.^[9]

References

External links

• International Chemical Safety Card 0799
• "NIOSH Pocket Guide to Chemical Hazards #0376". National Institute for Occupational Safety and Health (NIOSH). 
• Chronic toxicity summary
• Maleic anhydride at Occupational Safety & Health Administration