Maleic Anhydride
A five-membered ring with a double bond and two carbonyls, which makes it both an acid source and a dienophile. Half of it goes into unsaturated polyester; the rest into lubricant additives, butanediol and speciality copolymers.
Molecular Structure
What is Maleic Anhydride?
Maleic anhydride is the cyclic anhydride of maleic acid — a five-membered ring holding two carbonyls and a carbon-carbon double bond. That combination gives it two independent modes of reaction. The anhydride ring opens with alcohols, amines and water to give esters, amides and the diacid. The double bond, sitting between two electron-withdrawing carbonyls, is unusually electron-poor and reacts readily as a dienophile in Diels-Alder chemistry and as a comonomer with electron-rich partners such as styrene.
It is made almost entirely by partial oxidation of n-butane over a vanadium phosphorus oxide catalyst, in fixed-bed or fluid-bed reactors. The older benzene oxidation route has been progressively displaced — benzene is a carcinogen, and two of its six carbons end up as carbon dioxide rather than product.
Unsaturated polyester resin is the largest outlet, where the residual double bond is what allows the polyester to crosslink with styrene. Beyond that, maleic anhydride feeds 1,4-butanediol and tetrahydrofuran by hydrogenation, lubricant dispersants via polyisobutylene succinic anhydride, styrene-maleic anhydride copolymers, and paper sizing agents.
Maleic anhydride is a respiratory sensitiser. Once someone has become sensitised, subsequent exposures at concentrations far below any general irritation threshold can trigger an asthmatic response — so the control target is preventing sensitisation in the first place, not managing an exposure limit.
Quick Reference
Key Physical & Chemical Properties
Structure & Bonding
A five-membered anhydride ring carrying a carbon-carbon double bond. Two carbonyls flank that double bond and pull electron density away from it, which is what makes maleic anhydride both a reactive acylating agent and an exceptionally good dienophile.
Skeletal structure — cyclic anhydride with a ring double bond
Structural Identity
- IUPAC NameFuran-2,5-dione
- Common namesMaleic anhydride, MAH, MA, cis-butenedioic anhydride
- Molecular FormulaC₄H₂O₃
- Molecular Weight98.06 g/mol
- Functional groupsCyclic anhydride, alkene
- Ring sizeFive — one oxygen, two carbonyls
- ReactivityAcylating agent and dienophile
- Hydrolyses toMaleic acid — exothermic
- Made fromn-Butane oxidation over VPO catalyst
- CAS Number108-31-6
- InChI KeyFPYJFEHAWHCUMM-UHFFFAOYSA-N
Product Specifications
Chelora supplies Maleic Anhydride in standard and custom grades. Contact us for specification sheets tailored to your process.
| Chemical name | Maleic anhydride |
|---|---|
| CAS Number | 108-31-6 |
| Molecular formula | C₄H₂O₃ |
| Molecular weight | 98.06 g/mol |
| Purity (min) | ≥ 99.50 wt% |
| Solidification point (min) | ≥ 52.5 °C |
| Maleic acid (max) | ≤ 0.30 wt% |
| Colour, molten (max) | ≤ 20 APHA |
| Colour after heat stability test (max) | ≤ 40 APHA |
| Iron (max) | ≤ 1.0 ppm wt |
| Ash (max) | ≤ 100 ppm wt |
| Non-volatile residue (max) | ≤ 0.05 wt% |
| Acetic and acrylic acid (max) | ≤ 0.05 wt% |
| Water (max) | ≤ 0.10 wt% |
| Recommended molten storage | 60 – 70 °C under nitrogen |
| Flash point | 102 °C (closed cup) |
| Autoignition temperature | 477 °C |
| Transport classification | UN 2215, Class 8, PG III |
Downstream Applications & Derivatives
Key derivative chains and industrial uses of Maleic Anhydride.
Unsaturated Polyester Resins
The largest outlet. The residual double bond survives esterification and provides the crosslinking site for styrene cure — marine and FRP laminates, cultured marble, buttons and construction panels.
Lubricant Additives
Reacted with polyisobutylene to give PIBSA, then aminated to succinimide dispersants — the additive that keeps soot and sludge suspended in engine oil.
1,4-Butanediol & THF
Hydrogenation gives butanediol, gamma-butyrolactone and tetrahydrofuran, feeding spandex, PBT, solvents and pyrrolidone chemistry.
SMA & Maleated Polymers
Styrene-maleic anhydride copolymers for heat-resistant engineering plastics, and maleated polypropylene and polyethylene as coupling agents in filled and glass-reinforced compounds.
Paper Sizing
Alkenyl succinic anhydride sizing agents that make paper and board water-resistant under alkaline papermaking conditions.
Food & Agro Acids
Isomerisation and hydration routes to fumaric acid, malic acid and aspartic acid, plus maleic hydrazide as a sprout suppressant for potatoes and onions.
Why source Maleic Anhydride through Chelora Petrochem?
Verified Origin
Full origin certification and asset-backed supply chain documentation — no grey-market supply.
Grade Flexibility
Briquette, flake and molten supplied. We specify against maleic acid content and the heat stability colour test, because free acid and colour on heating are what determine how the material behaves in resin cook rather than the assay.
Full Documentation
CoA, SDS, UN 2215 transport documents, REACH compliance, respiratory sensitiser communication, and destination-market certificates with every shipment.
Logistics Support
Experienced in both bagged and heated bulk logistics — bagged and drummed briquettes, and insulated, nitrogen-blanketed ISO tanks for molten delivery, Indian and international.
Storage & Handling Guidelines
Always refer to the full SDS before handling. The following is a summary of key requirements.
- Keep moisture away from the material at all times. Maleic anhydride hydrolyses to maleic acid on contact with water, the reaction is exothermic, and the acid formed neither melts nor performs like the anhydride.
- Store solid material sealed, dry and cool, and store molten material at 60–70 °C under a dry nitrogen pad. Holding molten above about 80 °C accelerates colour development and sublimation.
- Control the vapour space on molten storage. Maleic anhydride sublimes readily, and the condensed solid blocks vents, relief lines and flame arrestors — a well-known cause of vent failures on MA tanks.
- Trace-heat and insulate all molten lines. The material freezes at 52.8 °C, and a plug is both a process failure and a pressure hazard if heating is applied to a blocked line.
- Prevent sensitisation rather than manage exposure. Enclose transfer points, extract at source, and treat any reported respiratory symptom as a signal to investigate the containment rather than to issue a respirator.
- Use stainless steel for wetted parts in molten service; iron drives colour and shows up on the heat stability test.
- Segregate from water, alkalis, amines, alcohols and strong oxidisers. Reaction with bases and amines is vigorous and exothermic.
- Manage dust from briquette and flake handling as both an irritant and a combustible dust issue — ground and bond conveying and control accumulation.
- Provide safety showers and eyewash at all handling points, and treat molten material as a thermal burn hazard on top of its corrosivity.
Hazard Summary
Classification: Skin Corr. 1B (H314), Resp. Sens. 1 (H334, may cause allergy or asthma symptoms or breathing difficulties if inhaled), Skin Sens. 1 (H317), Acute Tox. 4 oral (H302), Eye Dam. 1 (H318), STOT SE 3 (H335).
Respiratory sensitisation is the defining occupational hazard: maleic anhydride is a recognised occupational asthmagen. The concern is not acute irritation but the induction of an immune response — once a worker is sensitised, later exposures at concentrations well below any irritant threshold can provoke asthma, and the effect is generally permanent. Control strategy should therefore aim at preventing sensitisation through containment and extraction, not at working to an exposure limit.
Corrosive: causes severe skin burns and serious eye damage. Molten material combines that with a thermal burn at 60–70 °C.
Reacts with water: hydrolysis to maleic acid is exothermic, and in a confined space with a large quantity of anhydride the heat release matters. Water ingress into a molten tank is a genuine incident scenario, not just a quality problem.
Sublimation and vent blockage: maleic anhydride sublimes from molten storage and recondenses as a solid in cooler parts of the system. Blocked vents and relief paths on MA tanks are a documented failure mode and need a specific inspection regime.
Incompatibilities: water, alkalis, amines, alcohols and oxidising agents. Reaction with strong bases and amines can be violent, and contamination with alkali in a molten tank has caused runaway decomposition.
Fire: a combustible solid with a flash point of 102 °C and autoignition at 477 °C. Combustion and thermal decomposition produce carbon monoxide and irritant vapours.
PPE minimum: chemical goggles and face shield, corrosive-rated gloves and clothing, heat protection for molten service, and respiratory protection where containment cannot be assured.
Consult the full SDS for exposure limits, health surveillance guidance, spill containment and emergency response before any use.
Frequently Asked Questions
Technical and commercial questions about Maleic Anhydride sourcing and specifications.
What is maleic anhydride used for?
Unsaturated polyester resin is the largest outlet, taking roughly half of global demand, because the double bond in maleic anhydride survives the esterification and gives the resin its crosslinking site for styrene cure. The rest is spread widely: lubricant dispersants made through polyisobutylene succinic anhydride, 1,4-butanediol and tetrahydrofuran by hydrogenation, styrene-maleic anhydride copolymers, maleated polyolefin coupling agents, alkenyl succinic anhydride paper sizing, and food and agricultural acids including fumaric and malic acid.
Why is respiratory sensitisation treated as the key hazard?
Because it changes the nature of the risk permanently. Most industrial irritants cause effects proportional to the dose, so an exposure limit is a workable control. A respiratory sensitiser induces an immune response, and once a worker is sensitised they can react asthmatically to concentrations far below anything that would trouble an unsensitised colleague — potentially ending their ability to work with the material at all. Maleic anhydride is a well-documented occupational asthmagen, so the control objective is to prevent sensitisation happening, which means containment and extraction rather than respirators and monitoring against a number.
Why is maleic anhydride shipped molten, and what does that require?
It melts at 52.8 °C, and resin producers melt it anyway, so molten delivery in insulated nitrogen-blanketed tanks avoids a thermal cycle and the dust exposure of handling briquettes. What it requires at the receiving end is heated storage held at 60–70 °C, a dry nitrogen pad, fully trace-heated lines, and — importantly — a maintenance regime for the vent and relief system, because maleic anhydride sublimes and recondenses as a solid in cooler sections. Blocked vents on MA tanks are a recognised failure mode. Briquettes and bagged flake remain the practical choice for smaller or intermittent consumption.
Why does moisture matter so much?
Because water converts maleic anhydride into maleic acid, and maleic acid is not a substitute for it. The anhydride ring is what makes the material reactive towards glycols in resin production; once hydrolysed, that reactivity is gone and the melting behaviour changes completely. The reaction is also exothermic, so water ingress into a hot storage tank releases heat as well as destroying product. The maleic acid figure on the certificate is effectively a measure of how much moisture the material has already seen.
What is the difference between the butane and benzene routes?
Both oxidise a hydrocarbon over a catalyst, but the economics and the hazards differ. The benzene route was the original and uses a molybdenum-vanadium catalyst, but benzene is a human carcinogen and two of its six carbon atoms are burned to carbon dioxide, so the atom economy is poor. The n-butane route over vanadium phosphorus oxide uses a cheaper, non-carcinogenic feedstock with all four carbons retained in the product, and it now accounts for the great majority of world capacity. Where a supplier still runs benzene feed it is usually because of local feedstock availability rather than preference.
What documentation does Chelora provide?
Every shipment includes a Certificate of Analysis covering purity, solidification point, maleic acid content, colour in the melt and after the heat stability test, iron, ash, non-volatile residue, acetic and acrylic acid and water; a Safety Data Sheet to GHS and REACH format; UN 2215 Class 8 dangerous goods documentation; the respiratory sensitiser communication that downstream users are entitled to; an origin certificate; and destination-market certificates where required.
Request a quote or specification sheet
Talk to Chelora's sourcing team about Maleic Anhydride grade, volume, logistics, documentation, and lead times. We respond within one business day.
