Key Chemical Reactions Maleic anhydride in water (hydrolysis): MA + H₂O → maleic acid (cis-butenedioic acid). The reaction is exothermic and rapid - keep MA dry at all times to preserve product quality and prevent warehouse heat buildup.  |  Maleic anhydride to maleic acid: Simple hydrolysis (above).  |  Maleic anhydride to fumaric acid: Maleic acid undergoes acid- or heat-catalyzed isomerization to the trans-isomer fumaric acid - a key commercial route for food-grade fumaric acid production.  |  Maleic acid to maleic anhydride: Thermal dehydration of maleic acid (≥135°C) regenerates MA - used in purification and recycling processes.  |  Cyclopentadiene + maleic anhydride: Classic Diels-Alder [4+2] cycloaddition, the textbook example of a diene synthesis reaction - gives the bicyclic endo-adduct quantitatively at room temperature.

Specification Item	Standard Grade Industry / Polymer	Limit
Appearance	White flaky or granular crystals, free of visible impurities and discoloration
Purity (Content)	≥ 99.5%	Core quality indicator
Melting Point	52.5–54.5 °C	Process compatibility indicator
Free Acid Content	≤ 0.2%	Affects reactivity & catalyst sensitivity
Color (Pt-Co)	≤ 20	Purity & appearance indicator
Flash Point	103 °C	Safe solid/molten handling
Storage Stability	6 months	Sealed, cool, dry warehouse (0–25°C)
Packaging Options	25 kg moisture-proof bag  |  500 kg jumbo bag  |  1000 kg IBC bag  |  Molten tanker truck (bulk)

The single largest end-use for maleic anhydride globally - accounting for ~50% of total consumption - is the production of unsaturated polyester resins (UPR). MA reacts with diols (e.g., propylene glycol, ethylene glycol) to form polyester chains containing reactive double bonds that crosslink with styrene upon curing, yielding thermosets with excellent mechanical strength, chemical resistance, and dimensional stability. UPR is the matrix resin for fiberglass-reinforced plastics (FRP/GRP) used in boat hulls, automotive body panels, pipes, storage tanks, and wind turbine blades.

MA is also a key monomer in alkyd resins for solvent-borne and water-borne paints, where it introduces reactive double bonds that improve crosslink density, hardness, and drying speed in architectural and industrial coatings.

Maleic anhydride grafted polyethylene (MAH-g-PE) and maleic anhydride grafted polypropylene (MAH-g-PP) are functionalized polyolefins produced by reactive extrusion of MA onto PE or PP backbones. The pendant anhydride groups transform non-polar polyolefins into reactive polymers capable of bonding with polar substrates (nylon, glass fiber, metals, EVOH), dramatically improving adhesion, compatibility, and interfacial strength in multilayer films, composite materials, and polymer alloys.

These MA-grafted polymers are widely used as compatibilizers in glass fiber–reinforced nylon composites, tie layers in multilayer food packaging films (PE/EVOH/PE), and coupling agents in wood-plastic composites - all high-growth segments in the specialty plastics market.

Maleic anhydride readily copolymerizes by alternating free-radical polymerization with a wide range of electron-rich comonomers:

In the coatings industry, MA-based resins deliver water-based, high-solids, and UV-cure coating systems with excellent adhesion, weather resistance, and low VOC emissions - meeting increasingly stringent environmental regulations in Europe and North America. MA is a crosslinker in powder coatings and a component in UV-curable inks and optical fiber coatings.

In plastics modification, MA acts as a compatibilizer, coupling agent, and reactive flame retardant precursor. MA-based intumescent flame retardant systems (e.g., MA reacting with polyols) are increasingly used in halogen-free cable jackets and construction materials complying with IEC and EN fire standards.

MA is the archetypal dienophile in Diels-Alder [4+2] cycloaddition reactions. Its reaction with cyclopentadiene (and maleic anhydride) is the textbook Diels-Alder demonstration, giving the bicyclic endo-anhydride adduct quantitatively at room temperature. Similarly, alpha-phellandrene and maleic anhydride react to give terpene-derived adducts used in resins and fragrances. These cycloadducts are starting materials for pharmaceutical intermediates, insecticides, and specialty polymer monomers.

MA also serves as an intermediate in fumaric acid production (maleic anhydride → maleic acid → isomerization → fumaric acid), a critical food additive and polymer monomer, and in malic acid production (maleic anhydride → maleic acid → hydration → malic acid).

In agriculture, MA is a building block for maleic hydrazide (a plant growth regulator/sprout inhibitor for stored potatoes and onions), and an intermediate in organophosphate pesticide synthesis. In pharmaceuticals, MA-derived succinic acid and malic acid are used as API salt-forming acids to improve drug solubility. In lubricants, poly(isobutylene-alt-maleic anhydride) derivatives are engine oil dispersants that prevent sludge buildup. MA is also a monomer for biodegradable polymers (poly(maleic acid) derivatives) in response to global sustainability demand.

⚠️ SAFETY NOTE: Maleic anhydride dust and vapors are irritating to eyes, skin, and respiratory tract. Prolonged skin contact causes burns. MA hydrolyzes exothermically with water - keep dry. Flash point 103°C; combustible solid/molten liquid. GHS Hazard: Acute Toxicity (inhalation) Category 4, Skin Corrosion Category 1B, Serious Eye Damage Category 1, Respiratory Sensitizer.

Market note: The maleic anhydride price per kg has historically ranged from USD 0.80–1.50/kg ex-China depending on feedstock cycles. ICIS and CW Group track benchmark prices monthly. Buyers monitoring the ICIS maleic anhydride price report should contact us for quarterly forward-pricing agreements that hedge against feedstock volatility. Request a current MA price quote →

Q: What is the CAS number for maleic anhydride?

The CAS number for maleic anhydride is 108-31-6. It is also registered under EINECS number 203-571-6. In customs and shipping documentation, use CAS 108-31-6 alongside its HS code 2917.14.00 (cyclic anhydrides of polycarboxylic acids). The compound is also known by the abbreviations MA and MAH, and by its IUPAC name 2,5-furandione or furan-2,5-dione.

Q: What is the melting point of maleic anhydride? What happens when it melts?

The maleic anhydride melting point is 52.5–54.5°C. This relatively low melting point means MA can become partially or fully molten in warm climates during summer transport and storage if not temperature-controlled. Molten MA (maleic anhydride molten) is a clear, colorless to pale yellow liquid. It solidifies back to white solid on cooling without quality degradation, provided it has not absorbed moisture. Many large industrial buyers prefer receiving MA in molten form via heated tanker truck, eliminating bag handling entirely and reducing unit cost.

Q: What is the difference between maleic anhydride and maleic acid?

Maleic anhydride (C₄H₂O₃, MA) is the cyclic anhydride formed by elimination of water from maleic acid. It is a solid at room temperature. Maleic acid (cis-butenedioic acid, C₄H₄O₄) is the open-chain diacid formed when MA hydrolyzes in water: MA + H₂O → maleic acid. The anhydride form is more reactive and easier to handle in bulk; the acid form is used in food, beverage acidification, and certain polymer applications. Commercially, maleic acid anhydride (i.e., MA) is the preferred intermediate - buyers who need maleic acid typically hydrolyze MA on-site.

Q: What is styrene maleic anhydride (SMA) and what are its uses?

Styrene maleic anhydride (SMA) is an alternating copolymer of styrene and maleic anhydride made by free-radical copolymerization. Depending on the styrene:MA ratio and molecular weight, SMA resins have different properties. Key styrene maleic anhydride uses include: (1) engineering thermoplastic for heat-resistant automotive interior parts, appliance housings, and electronic connectors; (2) compatibilizer for PC/ABS and PPE/PA polymer blends; (3) reactive resin for photoresists and lithography materials; (4) after partial hydrolysis, as an emulsifier and dispersant for agricultural formulations. Poly(styrene-co-maleic anhydride) and poly(styrene-alt-maleic anhydride) grades are both available depending on comonomer ratio.

Q: What is the cyclopentadiene and maleic anhydride reaction?

The reaction between cyclopentadiene and maleic anhydride is the most famous example of a Diels-Alder [4+2] cycloaddition. Cyclopentadiene (the diene) reacts with maleic anhydride (the dienophile) at room temperature in quantitative yield to give the bicyclic endo-norbornene-2,3-dicarboxylic anhydride adduct. This reaction is widely taught in undergraduate organic chemistry as the textbook Diels-Alder demonstration due to its speed, clean reaction, and easily isolated crystalline product. The adduct is used industrially as a monomer for specialty polyimide and polyester resins with high thermal stability.

Q: How is maleic anhydride produced from n-butane vs benzene?

Both routes use catalytic vapor-phase oxidation. In the benzene oxidation route (older, benzene → MA), two of benzene's six carbons are lost as CO₂, making it inherently wasteful and generating more greenhouse gas per ton of MA. In the modern n-butane oxidation route (butane to maleic anhydride), n-butane (C₄H₁₀) is selectively oxidized over a vanadium-phosphorus-oxide (VPO) catalyst with 100% carbon atom utilization - all four carbons become part of the MA molecule. The butane route produces lower cost, has a better environmental footprint, and is now the standard for all new capacity globally. China's newer plants are predominantly butane-based, giving Chinese suppliers a cost advantage in the global MA market.