PRODUCTS

MALEIC ANHYDRIDE

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.

MALEIC ANHYDRIDE

CAS No. : 108-31-6
EC No. : 203-571-6

Synonyms:
Furan-2,5-dione; Maleic anhydride; cis-Butenedioic anhydride; 2,5-Furanedione; Maleic acid anhydride; Toxilic anhydride; MALEIC ANHYDRIDE; 2,5-Furandione; 108-31-6; furan-2,5-dione; Maleic acid anhydride; Toxilic anhydride; cis-Butenedioic anhydride; Dihydro-2,5-dioxofuran; Polymaleic anhydride; Maleinanhydrid; 2,5-dihydrofuran-2,5-dione; RCRA waste number U147; 2,5-Furandione, homopolymer; Poly(maleic anhydride); Maleinanhydrid [Czech]; Maleic anhydride polymer; NSC 137651; Maleic anhydride oligomer; Anhydrid kyseliny maleinove; Poly(maleic acid anhydride); Maleic anhydride, homopolymer; CCRIS 2941; HSDB 183; Maleic acid anhydride homopolymer; Maleic Anhydride; Anhydrid kyseliny maleinove [Czech]; MAH/Maleic Anhydride; EINECS 203-571-6; Maleic anhydride, polymers; RCRA waste no. U147; MALEIC ANHYDRIDE; MA; Maleic anhydride polymer, phenyl-terminated; Maleic anhydride, homopolymer, diphenyl terminated; Maleic Anhydrides; Maleic anhydride, 99%, pellets; 2,5-Furanedione; fumaric anhydride; furan-2,5-quinone; Sodium n-amylxanthate; PubChem16845; ACMC-1CROF; Maleic anhydride, 99%; Maleic Anhydride (MAN); Furan-2,5-dione; Maleic anhydride; cis-Butenedioic anhydride; 2,5-Furanedione; Maleic acid anhydride; Toxilic anhydride; MALEIC ANHYDRIDE; 2,5-Furandione; Epitope ID:122673; EC 203-571-6; ma; Lytron 810 (Salt/Mix); Lytron 820 (Salt/Mix); Maleic anhydride, briquettes; Maleic anhydride (briquette); Maleic anhydride treated BSA; 24937-72-2; 5-17-11-00055 (Beilstein Handbook Reference); KSC177I6H; (Z)-butanedioic acid anhydride; Maleimide-Related Compound 11; Maleic anhydride, powder, 95%; Maleic anhydride [UN2215] [Corrosive]; Maleic anhydride, for synthesis, 99.0%; SC-79370; Maleic anhydride [UN2215] [Corrosive]; Maleic anhydride treated bovine serum albumin; ST51046487; Maleic anhydride, puriss., >=99.0% (NT); Maleic anhydride, SAJ first grade, >=98.0%; Maleic anhydride treated non-fat dry milk powder; Maleic anhydride, 95% (may contain up to 5% maleic acid); MAN

Maleic Anhydride

Properties
Chemical formula C4H2O3
Molar mass 98.057 g·mol−1
Appearance White crystals or needles[3]
Odor irritating, choking[3]
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)[3]
Magnetic susceptibility (χ) -35.8·10−6 cm3/mol

Production
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. Traditionally maleic anhydride was produced by the oxidation of benzene or other aromatic compounds. As of 2006, only a few smaller plants continue to use benzene.

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 vanadium phosphate is used for the butane route:

C4H10 + 3.5 O2 → C4H2O3 + 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.

The traditional method using benzene became uneconomical due to the high and still rising benzene prices and by complying with the regulations of benzene emissions. In addition, in the production of maleic anhydride (4 C-atoms) a third of the original carbon atoms is lost as carbon dioxide when using benzene (6 carbon atoms). The modern catalytic processes start from a 4-carbon molecule and only attaches oxygen and removes water; the 4-C-base body of the molecule remains intact. Overall, the newer method is therefore more material efficient.[6]

Parallels exist with the production of phthalic anhydride: While older methods use naphthalene, modern methods use o-xylene as feedstock.

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.[7] It was used for work in 1928, on the reaction between maleic anhydride and 1,3-butadiene, for which 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.

Maleic anhydride Diel.Alder reaction with butadiene.svg
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.[8]

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.[9]

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

On account of its cycle of 4 π electrons in an array of 5 atoms with p orbitals, maleic anhydride was long thought to exhibit antiaromaticity. However, a thermochemical study concluded that only 8 kJ/mol of destabilization energy can be ascribed to this effect, making it weakly antiaromatic at best.[10]

Uses
Maleic anhydride is used in many applications.

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 that are used in a wide range of applications such as pleasure boats, bathroom fixtures, automobiles, tanks and pipes.

Maleic anhydride is hydrogenated to 1,4-butanediol (BDO), used in the production of thermoplastic polyurethanes, elastane/Spandex fibers, polybutylene terephthalate (PBT) resins and many other products.

Applications
Maleic anhydride has a very broad range of uses from food additives to industrial applications.

USAGE AREAS
Synthetic resin raw material (unsaturated polyesters)
Paints and coatings
Resin modifiers
Vinyl chloride stabilizers
Food additives (fumaric acid, succinic acid, malic acid)
Agricultural chemicals
Paper sizing agents
Imides
Surfactants
Plasticizers (DOM, DBM, DEM)
Other (GBL, 14BG, THF)

Malathion is a popular insecticide that is derived from maleic anhydride.

Structure of sodium sulfosuccinate esters, common class of surfactants derived from maleic anhydride.

Alkenylsuccinic anhydrides, which are derived from maleic anhydride, are widely used in papermaking.
Diels-Alder reaction of maleic anhydride and butadiene and isoprene gives the respective tetrahydrophthalic anhydrides which can be hydrogenated to the corresponding hexahydrophthalic anhydrides. These species are used as curing agents in epoxy resins. 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.

A number of smaller applications for maleic anhydride. The food industry uses malic acid which is derivative of 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 a precursor to compounds used for water treatment detergents, insecticides and fungicides, pharmaceuticals, and other copolymers.

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 pellets are transported by trucks. Packaging is generally in 25 kg polyethylene bags.

USES
Maleic anhydride is used primarily in the formation of unsaturated polyester resins for use in boats, autos, trucks, buildings, piping, and electrical goods. Lube oil adhesives synthesized from maleic anhydride are used to prolong oil-change intervals and improve engine efficiency. Maleic anhydride is also used to make copolymers, pesticides, and other organic compounds, and in Diels-Alder syntheses.

MAN – Maleic Anhydride – is a low molecular weight, unsaturated, carboxylic anhydride. The clear, colorless molten product is available in rail tank cars, tank trucks, and ISO (intermodal) tank containers.

In coating resins Maleic anhydride
Introduces cure sites for crosslinking in reactive cure coatings like alkyds
Provides a reactive site for UV-cured coatings
Elevates glass transition temperature to improve hardness and shorten dry times

Maleic anhydride is a versatile chemical platform with two distinctive reactive sites and is
An essential component in making unsaturated polyester resins
Key to many lubricating oil additives, dispersants and corrosion inhibitors
Necessary to prepare alkenyl succinic anhydrides (ASA) used in paper sizing, detergents, oil field chemicals, and epoxy curing agents
Reacted into copolymers with vinyl ethers, styrene, and acrylic acid used in adhesives, textiles, cosmetics, toothpaste, emulsifiers, dispersants, paints and inks
Used to synthesize malic acid for flavor enhancement and pH control in food and beverages
An intermediate leading to fumaric acid, agricultural chemicals, water treatment agents, fire retardants, and sweeteners

Effects on human health and the environment
This compound poses relatively low-risk environmental hazards, an important feature for some applications. In humans, exposure to maleic anhydride may cause irritation to the respiratory tract, eyes, exposed mucosa, and skin. Maleic anhydride is also a skin and respiratory sensitizer.[11]

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 itself are unlikely. Maleic acid is biodegradable under aerobic conditions in sewage sludge as well as in soil and water.

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.

Maleic anhydride appears as colorless crystalline needles, flakes, pellets, rods, briquettes, lumps or a fused mass. Melts at 113°F. Shipped both as a solid and in the molten state. Vapors, fumes and dusts strong irritate the eyes, skin and mucous membranes. Flash point 218°F. Autoignition temperature 890°F. Used to make paints and plastics and other chemicals.

Maleic anhydride is a cyclic dicarboxylic anhydride that is the cyclic anhydride of maleic acid. It has a role as an allergen. It is a cyclic dicarboxylic anhydride and a member of furans.

Maleic anhydride is used in the formulation of resins. Exposure to maleic anhydride may occur from accidental releases to the environment or in workplaces where it is produced or used. Acute (short-term) inhalation exposure of humans to maleic anhydride has been observed to cause irritation of the respiratory tract and eye irritation. Chronic (long-term) exposure to maleic anhydride has been observed to cause chronic bronchitis, asthma-like attacks, and upper respiratory tract and eye irritation in workers. In some people, allergies have developed so that lower concentrations can no longer be tolerated. Kidney effects were observed in rats chronically exposed to maleic anhydride via gavage (experimentally placing the chemical in the stomach). EPA has not classified maleic anhydride for carcinogenicity.

Dogs were fed 60 mg/kg/day maleic anhydride for 990 days. The plasma levels of maleic anhydride were determined. An uptake rate constant of 3.49X10-3/day and an elimination rate constant of 8.32X10-2/day were calculated assuming a one compartment model. According to the model 99% of steady state was reached by day 55 of the study. The dogs were maintained at steady state for the final 35 days of study.

Maleic anhydride has a rather low order of toxicity via the dermal route indicating limited absorption via this route.

Maleic anhydride is probably hydrolyzed to maleic acid and then hydroxylated to malic acid, which participates in the Krebs cycle or may be excreted unchanged or in conjugated form. Maleic acid is an antimetabolite of fumaric acid.

IDENTIFICATION: Maleic anhydride appears as colorless needles or white lumps or pellets. It has an irritating, choking odor. Maleic anhydride is very soluble in water and readily reacts with water to form maleic acid.

USE:
Maleic anhydride is used to make other chemicals that are used in resins, dyes, drugs and agriculture.

EXPOSURE: Workers handling maleic anhydride in manufacturing may breathe in vapors or have direct skin contact. Exposure is unlikely in the general population. If maleic anhydride is released to the environment, it will react with water to form maleic acid within minutes. Due to rapid reaction with water, the likelihood of maleic anhydride binding to particles in soil and water, being broken down by microorganisms in soil and water, moving through soil, or moving into the air from soil or water surfaces is low. If maleic anhydride is released to air, it will be degraded by reaction with other chemicals and light. RISK: Respiratory irritation, chronic bronchitis, and asthma have been reported in workers that breathed very low concentrations of maleic anhydride vapor or dust. Skin irritation and allergic reactions and eye irritation have also been reported in workers following exposure to maleic anhydride vapor or dust. Skin irritation and sensitization have been observed in laboratory animals exposed to maleic anhydride, and severe eye irritation occurred with direct contact. Respiratory and eye irritation, breathing difficulty, lesions in the nose and lung, and decreased body weight were found in laboratory animals repeatedly exposed to low-to-moderate concentrations of maleic anhydride vapors. No changes in fertility or increases in birth defects or abortions were observed in laboratory rats given moderate oral doses of maleic anhydride over two-generations. No tumor formation was observed in laboratory animals exposed to low concentrations of maleic anhydride vapors for 6 months or fed low-to-moderate doses of maleic anhydride for 2 years. The American Conference of Governmental Industrial Hygienists has determined that maleic anhydride is not classifiable as a human carcinogen based on lack of tumor formation in a limited number of laboratory animal studies and no data in humans. The potential for maleic anhydride to cause cancer in humans has not been assessed by the U.S. EPA IRIS program, International Agency for Research on Cancer, or the U.S. National Toxicology Program 13th Report on Carcinogens.

Because of its properties as a dicarboxylic anhydride with a double bond, MA /maleic anhydride/ can be used for both polycondensation and polyaddition. Polyester and alkyd resins, lacquers, plasticizers, copolymers, and lubricants are the most important technical end products. Examples of industrially important copolymers are: MA-styrene (for engineering plastics) and MA-acrylic acid (used in the detergent industry). Polyester and alkyd resins, in particular, are used in the production of fiberglass reinforced plastics, in the construction and electrical industries, and in pipeline and marine construction. ... Smaller amounts of MA are used in the production of pesticides (captan, malathion) and growth inhibitors (maleic acid hydrazide). ... When added to drying oils, MA reduces the drying time and improves the coating quality of lacquers.

Maleic anhydride is readily hydrolyzed to maleic acid under aqueous conditions. As a result, these two chemicals are presented because of the conditions used to test their toxicity. The only difference may be due to the potential for maleic anhydride to form haptens by acylating with amino acids, resulting in an immunological response (dermal and respiratory sensitization).

In addition to making maleic anhydride by a conventional n-butene fixed bed process, a new process based on a fluidized bed reactor system has been commercialized.

Maleic anhydride is a waste chemical stream constituent which may be subjected to ultimate disposal by controlled incineration. Controlled incineration; care must be taken that complete oxidation to nontoxic products occurs.

Residues of maleic acid and maleic anhydride are exempted from the requirement of a tolerance when used in accordance with good agricultural practice as inert (or occasionally active) ingredients in pesticide formulations applied to growing crops only. Use: Stabilizer. Limit: For pesticide formulations applied to apples with a minimum preharvest interval of 21 days.

Maleic anhydride is designated as a hazardous substance under section 311(b)(2)(A) of the Federal Water Pollution Control Act and further regulated by the Clean Water Act Amendments of 1977 and 1978. These regulations apply to discharges of this substance. This designation includes any isomers and hydrates, as well as any solutions and mixtures containing this substance.

Maleic anhydride is an indirect food additive for use only as a component of adhesives.

Maleic anhydride retarded the carcinogenic activity of benzo(a)pyrene and dibenzo(a,h)anthazene when applied together with these carcinogens to mice dermally.

USE:
Maleic anhydride is a solid substance appearing as colorless needles or white crystalline solid. Maleic anhydride is an intermediate, which is used in a wide range of products, mainly in the manufacture of unsaturated polyester resins.

HUMAN EXPOSURE AND TOXICITY: Maleic anhydride is irritating to skin in humans. Severe skin burns and itching have been reported following dermal contact. Dust or vapor has been reported to cause conjunctivitis, inflammation and swelling of the eyelids, severe lacrymation and photophobia. Case reports of respiratory irritation, and feelings of nasal irritation and pulmonary discomfort in a volunteer study indicate that maleic anhydride is a respiratory irritant. In the volunteer study, impairment of smell was also reported. A single worker showed a positive skin reaction to a patch test, indicating that skin sensitisation was present. Repeated exposure of workers is associated with asthma as evidenced by a number of case reports. It is not known if the asthma has an immunological background.

ANIMAL STUDIES: Inhalation exposure for 6 hours to up to 199 mg/cu m of maleic anhydride vapor did not cause mortality in rats. At the highest concentration, signs of eye and nose irritation were observed. Direct contact with maleic anhydride powder caused severe skin irritation in rabbits, and a 1% solution was highly irritating to their eyes. The principal effects identified in four-week and six-month inhalation studies in rats, hamsters, and Rhesus monkeys were lesions in the respiratory tract including the nose, trachea and lungs. In two rat studies (90 days or 90 and 183 days), dietary administration of maleic anhydride resulted in nephritis. In a two-generation rat study with gavage administration, no effects on fertility were found, however the pregnancy rate of the control group was exceptionally low (50-70%). The only developmental effect seen was a slight reduction in body-weight of pups from the first litter of the first generation, at this dose level (150 mg/kg b.w./day) severe toxicity including mortality was found in the parental animals. Maleic anhydride was negative in the Ames test. An in vitro chromosome aberration test showed a positive effect. An in vivo chromosome aberration test was negative. No treatment-related differences in tumor incidence were found in a dietary carcinogenicity study in rats.

ECOTOXICITY STUDIES: Median tolerance limit for Gambusia affinis (mosquitofish) was found to be 240 mg/L/24 or 48 hr and 230 mg/L/96 hr in a static test done in pond water of high turbidity; 20-23 °C, pH 5.8-8.0, aerated; fish treated with terramycin to prevent or treat tail-rot disease. The LC100 was 320 mg/L/24 hr.

Uninjured workers reported nasal irritation within 1 min followed by eye irritation in 15 min at 1.5-2 ppm. Levels >/= 2.5 ppm are extremely irritating. One reference indicates that at 0.5 ppm there is a faint odor without irritation at around 0.25 ppm. The frequency of chronic bronchitis among workers exposed over many years to maleic anhydride is much greater than among those with similar exposures to phthalic anhydride.

Chronic toxicity and oncogenicity were evaluated in male and female Fischer 344 rats (504 males, 501 females; number/group not reported) exposed orally to maleic anhydride in the diet at 0, 10, 32 and 100 mg/kg/day for 2 yrs. There were significant differences between treated and control animals in the following: red blood cell count (at 6 months, decreased in males at all dose levels, females at high and low dose levels; at 12 months, decreased for males at low dose), hematocrit levels (at 6 months, decreased for males at high and low doses), and thyroid clear cell adenomas and hyperplasia (females at all doses, not considered to be treatment related). There were no significant differences between treated and control animals in the following: body and organ weights, mortality, neurology, ophthalmology, or urinalysis.

The mutagenicity of maleic anhydride (MA) was evaluated in Salmonella tester strains TA98, TA100, TA1535, TA1537, and TA1538, both in the presence and absence of added metabolic activation by Aroclor-induced rat liver S9 fraction. MA was tested for mutagenicity at concentrations up to 500 ug/plate using the quantitative overlay method. MA did not cause a positive response in any of the bacterial tester strains, either with or without metabolic activation.

The ability of maleic anhydride to cause chromosome aberrations in the bone marrow cells was examined in male and female Sprague-Dawley rats (15/sex/group) exposed by inhalation at concentrations of 0, 1, or 100 mg/cu m for a single 6-hr exposure. Five rats/sex/group were sacrificed 6, 24, and 48 hrs after termination of exposure and 50 cells/animal were scored for chromosome aberrations. There were no differences between treated and control animals with respect to the frequency of chromosome aberrations in bone marrow cells.

The plasma levels of maleic anhydride were evaluated in purebred beagle dogs (4/sex) ingesting test material in the diet at doses of 60mg/kg/day for 90 days. Plasma samples were obtained on days 1, 3, 12, 29 and 90 days on study for measurement of maleic anhydride. The data was analyzed by nonlinear parameter estimation program. Assuming the one compartment model, an uptake rate constant of 3.49 x 10(-3) days(-1) and an elimination rate of 8.32 x 10(-2) days(-1) were obtained. The model therefore predicates that steady-state was reached on day 55 of the study.

Maleic anhydride's production and use as a chemical intermediate in production of resins, dye intermediates, pharmaceuticals, agricultural chemicals and polymers may result in its release to the environment through various waste streams. It has been suggested that in-situ formation of maleic anhydride in the ambient atmosphere may be possible via photooxidation of aromatic hydrocarbons (benzene, toluene, xylene); the hydrolysis product of maleic anhydride has been found in rainwater samples. If released to air, a vapor pressure of 0.25 mm Hg at 25 °C indicates maleic anhydride will exist solely as a vapor in the atmosphere. Vapor-phase maleic anhydride will be degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals, ozone molecules and nitrate radicals with half-lives 11 days, 6.5 days and 8 hours, respectively. Atmospheric reaction with nitrate radicals is an important night time sink for maleic anhydride. Maleic anhydride absorbs at wavelengths >290 nm and, therefore, may be susceptible to direct photolysis by sunlight. If released to soil, maleic anhydride is expected to have very high mobility based upon an estimated Koc of 1. However, maleic anhydride hydrolyzes rapidly in water forming maleic acid.

Therefore, potential leaching in soil is expected to be dominated by degradation to maleic acid. Volatilization from moist soil surfaces is not expected to be an important fate process due to hydrolysis. Maleic anhydride is not expected to volatilize from dry soil surfaces based upon its vapor pressure. Various biodegradation screening tests have found maleic anhydride to be readily biodegradable. However, available biodegradation rates for maleic anhydride are expected to reflect the hydrolysis product maleic acid. If released into water, maleic anhydride will hydrolyze rapidly with half-lives of 3.32 and 0.37 minutes at 0 and 25.1 °C, respectively. Volatilization from surface waters and bioconcentration in aquatic organisms is unlikely due rapid hydrolysis. Occupational exposure to maleic anhydride may occur through inhalation and dermal contact with this compound at workplaces where maleic anhydride is produced or used. Monitoring and use data indicate that the general population may be exposed to maleic anhydride via inhalation of ambient air.

Maleic anhydride's production and use as a chemical intermediate in production of resins, dye intermediates, pharmaceuticals, agricultural chemicals and polymers(1) may result in its release to the environment through various waste streams(SRC). It has been suggested that in-situ formation of maleic anhydride in the ambient atmosphere may be possible via photooxidation of aromatic hydrocarbons (benzene, toluene, xylene) which has been demonstrated in laboratory studies(2); maleic acid, the hydrolysis product of maleic anhydride has been found in rainwater samples(2).

Based on a classification scheme(1), an estimated Koc value of 1(SRC), determined from a structure estimation method(2), indicates that maleic anhydride is expected to have very high mobility in soil(SRC). However, maleic anhydride hydrolyzes rapidly in water forming maleic acid with hydrolysis half-lives of 3.32 and 0.37 minutes at 0 and 25.1 °C respectively(3). Therefore, potential leaching in soil is expected to be dominated by degradation to maleic acid(SRC). Volatilization of maleic anhydride from moist soil surfaces is not expected to be an important fate process due to hydrolysis(SRC). Maleic anhydride is not expected to volatilize from dry soil surfaces(SRC) based upon a vapor pressure of 0.25 mm Hg at 25 °C(4). Various biodegradation screening tests have found maleic anhydride to be readily biodegradable(5,6). However, available biodegradation rates for maleic anhydride are expected to reflect the hydrolysis product maleic acid(SRC).

Based on a classification scheme(1), an estimated Koc value of 1(SRC), determined from a structure estimation method(2), indicates that maleic anhydride is not expected to adsorb to suspended solids and sediment(SRC). Volatilization from water surfaces is expected(3) based upon an estimated Henry's Law constant of 3.9X10-6 atm-cu m/mole(SRC), developed using a fragment constant estimation method(2). However, maleic anhydride hydrolyzes rapidly in water forming maleic acid with hydrolysis half-lives of 3.32 and 0.37 minutes at 0 and 25.1 °C, respectively(3). Therefore, volatilization is not expected to be an important fate process in water due to hydrolysis(SRC). Bioconcentration of maleic anhydride in aquatic organisms is unlikely due its rapid hydrolysis(SRC). Various biodegradation screening tests have found maleic anhydride to be readily biodegradable(5,6). However, available biodegradation rates for maleic anhydride are expected to reflect the hydrolysis product maleic acid(SRC).

According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), maleic anhydride, which has a vapor pressure of 0.25 mm Hg at 25 °C(2) is expected to exist solely as a vapor in the ambient atmosphere. Vapor-phase maleic anhydride is degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals(SRC); the half-life for this reaction in air is estimated to be 11 days(SRC), calculated from its rate constant of 1.45X10-12 cu cm/molecule-sec at 23 °C(3). Vapor-phase maleic anhydride is also degraded in the atmosphere by reaction with ozone(SRC); the half-life for this reaction in air is estimated to be 6.5 days, calculated from its estimated rate constant of 0.18X10-17 cu cm/molecule-sec at 25 °C that was derived using a structure estimation method(4). The nitrate radical (NO3) is the dominant atmospheric oxidant during the night-time in most atmospheric environments(5). Vapor-phase maleic anhydride is degraded in the atmosphere by reaction with nitrate radicals(SRC); the half-life for this reaction in air is estimated to be 8 hours(SRC), calculated from its rate constant of 1.0X10-13 cu cm/molecule-sec at 25 °C(6). Removal of maleic anhydride via reaction with hydroxyl radicals, ozone and nitrate radicals leads to the formation of dicarbonyls(7). Maleic anhydride absorb at wavelengths >290 nm(6) and, therefore, may be susceptible to direct photolysis by sunlight(SRC). In the vapor phase, hydrolysis of maleic anhydride is completed in 21 hr at 96% relative humidity while no hydrolysis occurs at 50% relative humidity(8).

Maleic anhydride, present at 100 mg/L, reached 54.8% of its theoretical BOD in 2 weeks using an activated sludge inoculum at 30 mg/L and the Japanese MITI test(1). Using OECD Guideline 301B (Ready Biodegradability: CO2 Evolution Test), maleic anhydride was found to be readily biodegradable with CO2 evolution rates of 61.6% after 4 days and 93.2% after 11 days(2); it was noted that maleic anhydride hydrolyzes under the test conditions and, as a result, maleic acid is believed to be the test material investigated in the study(2). Another OECD Guideline 301B test determined >90% CO2 evolution within 25 days(2). Using OECD Guideline 301E (Ready Biodegradability: Modified OECD Screening Test) and a non-adapted activated sludge inoculum, maleic anhydride was found to be readily biodegradable with a 73-81% removal after 28 days(2). The TOC and COD-Mn of maleic anhydride, present at 170 mg/L in industrial wastewater, was reduced by 98% and 99%, respectively, after 1 day of acclimation with an activated sludge inocculum from a waste water treatment plant(3). In one report 99% removal was achieved in 4 hr by activated sludge(4). Others report 40-60% theoretical BOD in 5 days with sewage inoculum(5,6). The data suggest that maleic anhydride is expected to biodegrade rapidly(SRC); however, maleic anhydride hydrolyzes rapidly in water forming maleic acid with hydrolysis half-lives of 3.32 and 0.37 minutes at 0 and 25.1 °C, respectively(7). Therefore, the available biodegradation rates are expected to correspond primarily to maleic acid(SRC).

The rate constant for the vapor-phase reaction of maleic anhydride with photochemically-produced hydroxyl radicals has been measured as 1.45X10-12 cu cm/molecule-sec at 23 °C(1). This corresponds to an atmospheric half-life of about 11 days at an atmospheric concentration of 5X10+5 hydroxyl radicals per cu cm(2). The rate constant for the vapor-phase reaction of maleic anhydride with ozone has been estimated as 0.18X10-17 cu cm/molecule-sec at 25 °C(SRC) that was derived using a structure estimation method(2). This corresponds to an atmospheric half-life of about 6.5 days at an atmospheric concentration of 7X10+11 ozone molecules per cu cm(2). The rate constant for the vapor-phase reaction of maleic anhydride with atmospheric nitrate radicals is reported as 1.0X10-13 cu cm/molecule-sec at 25 °C(3). This corresponds to an atmospheric half-life of about 8 hours(SRC) at a nighttime atmospheric concentration of 2.5X10+8 nitrate radicals per cu cm(4). Maleic anhydride absorbs at wavelengths >290 nm(3) and, therefore, may be susceptible to direct photolysis by sunlight(SRC). Maleic anhydride hydrolyzes in water at room temperature forming maleic acid(5). The first-order hydrolysis rate constants, in initially neutral solution, at 0 and 25.1 °C were measured as 0.00348 and 0.03140 per second(6) which correspond to half-lives of 3.32 and 0.37 minutes respectively(SRC). In the vapor phase, hydrolysis of maleic anhydride is completed in 21 hr at 96% relative humidity while no hydrolysis occurs at 50% relative humidity(7).

An estimated BCF of 5 was calculated in fish for maleic anhydride(SRC), using an estimated log Kow of 1.62(1) and a regression-derived equation(1). According to a classification scheme(2), this BCF suggests the potential for bioconcentration in aquatic organisms is low(SRC). In addition, maleic anhydride hydrolyzes rapidly in water forming maleic acid with hydrolysis half-lives of 3.32 and 0.37 minutes at 0 and 25.1 °C respectively(3). Bioconcentration of maleic anhydride in aquatic organisms is unlikely due its rapid hydrolysis(SRC).

Using a structure estimation method based on molecular connectivity indices(1), the Koc of maleic anhydride can be estimated to be 1(SRC). According to a classification scheme(2), this estimated Koc value suggests that maleic anhydride is expected to have very high mobility in soil. However, maleic anhydride hydrolyzes rapidly in water forming maleic acid with hydrolysis half-lives of 3.32 and 0.37 minutes at 0 and 25.1 °C respectively(3). Therefore, potential leaching in soil is expected to be dominated by degradation to maleic acid(SRC).

The Henry's Law constant for maleic anhydride is estimated as 3.9X10-6 atm-cu m/mole(SRC) using a fragment constant estimation method(1). This Henry's Law constant indicates that maleic anhydride is expected to volatilize from water surfaces(2). However, maleic anhydride hydrolyzes rapidly in water forming maleic acid with hydrolysis half-lives of 3.32 and 0.37 minutes at 0 and 25.1 °C respectively(3). Therefore, volatilization is not expected to be an important fate process in water or moist soils(SRC). Maleic anhydride is not expected to volatilize from dry soil surfaces(SRC) based upon a vapor pressure of 0.25 mm Hg at 25 °C(4).

The primary emission sources in descending order are phthalic anhydride production, maleic anhydride production, end product manufacturing, and packaging losses.

Maleic anhydride can be found at 100-600 ppm (by volume) in the unabated process exhaust of phthalic anhydride manufacturing plants(1).

Maleic anhydride is reported to be a constituent of coffee aroma(1).

Maleic anhydride was identified as an organic disinfection byproduct in a drinking water pilot plant in Evansville, IN which used chlorine dioxide as a primary disinfectant(1).

NIOSH (NOES Survey 1981-1983) has statistically estimated that 81,551 workers (14,807 of these are female) are potentially exposed to maleic anhydride in the US(1). Occupational exposure to maleic anhydride may occur through inhalation and dermal contact with this compound at workplaces where maleic anhydride is produced or used(SRC). Monitoring and use data indicate that the general population may be exposed to maleic anhydride via inhalation of ambient air(SRC).

General description
The structure of maleic acid consists of four carbon molecules along with carboxylate groups on either ends, with a double bond between the central carbon atoms. The anhydride of maleic acid has five atoms in its cyclic molecule, the unsaturated bond undergoes free radical polymerization in the presence of an initiator.

Application
Maleic anhydride may be used in the synthesis of unsaturated polyester resins and as a reactant in synthesizing important products such as agricultural chemicals, lubricant additives and food acidulatents.

Maleic anhydride is produced by oxidation of benzene or a C4 hydrocarbon such as butane in the presence of a vanadium oxide catalyst. Maleic anhydride can be converted to maleic acid by hydrolysis and to esters by alcoholysis.