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CHEMINFO Record Number: 652
CCOHS Chemical Name: Maleic acid

(z)-2-Butenedioic acid
cis-Butenedioic acid
(z)-1,2-Ethylenedicarboxylic acid
cis-1,2-Ethylenedicarboxylic acid
Maleinic acid
Malenic acid
Toxilic acid
Acide maléique

Chemical Name French: Acide maléique
Chemical Name Spanish: Acido maleico
CAS Registry Number: 110-16-7
RTECS Number(s): OM9625000
EU EINECS/ELINCS Number: 203-742-5
Chemical Family: Unsaturated aliphatic carboxylic acid / unsaturated aliphatic dicarboxylic acid / alkenoic acid / alkene dioic acid
Molecular Formula: C4-H4-O4
Structural Formula: HO-C(=O)-HC=CH-C(=O)-OH (cis isomer)


Appearance and Odour:
White crystals or powder with a faint acid odour.(10,11)

Odour Threshold:
Not available

Warning Properties:
Information not available for evaluation.

Maleic acid is the cis isomer of 2-butenedioic acid. Fumaric acid (CHEMINFO 739) is the trans isomer. Maleic acid is commercially available as the crystalline material or as an aqueous solution in water (40%). It may contain fumaric acid (0.1%) and water (less than 0.5%) as impurities.(12)

Uses and Occurrences:
Maleic acid is not very important economically, since the anhydride is easier to use.(12) It is used in the manufacture of phthalic-type alkyd and polyester resins, surface coatings, copolymers, plasticizers, lubricant additives and agricultural chemicals; in adhesives and sealants; as a preservative for oils and fats; organic synthesis; dyeing and finishing wool, cotton and silk; and preparing the maleate salts of antihistamines and similar drugs.(10,13,14)


White crystals or powder with a faint acid odour. Probably can burn if strongly heated. POTENTIAL COMBUSTIBLE DUST HAZARD. Powdered material may form explosive dust-air mixtures. CORROSIVE to the eyes and skin. Can cause permanent eye damage, including blindness, or permanent scarring of the skin.


Effects of Short-Term (Acute) Exposure

Maleic acid mists (from solutions) or dusts can probably cause mild to severe irritation, based on limited animal information. The severity of the effect would depend on the strength of solution, airborne concentration and duration of exposure. Symptoms of exposure would include sore throat, nasal irritation and coughing. There is no human information available.

Skin Contact:
Contact with liquid (from solutions) or dusts can probably cause at least moderate irritation, based on animal information. Symptoms would include redness, pain and swelling. The severity of the effects would depend on the acid concentration and duration of exposure. Although animal information does not indicate that maleic acid is corrosive to the skin, concentrated solutions are highly acidic and would be expected to cause corrosive effects (tissue death), based on their pH. Depending on the concentration of the solution and the degree of exposure, corrosive materials may cause permanent scarring.

Eye Contact:
The liquid, mists or dusts can cause severe irritation or injury (corrosive effects), based on animal information. The severity of the effect would depend on the concentration of the solution and duration of contact. Corrosive materials may cause permanent eye damage, including blindness.

Toxic effects, including deaths, have been observed following ingestion of high concentrations of maleic acid in the diet. However, these high doses are not considered relevant to occupational exposures. Ingestion is not a typical route of occupational exposure.

Effects of Long-Term (Chronic) Exposure

SKIN CONTACT: Prolonged or repeated contact with dusts or dilute solutions may result in redness, swelling, and thickening of the skin (dermatitis).


There is no human or animal information available.

The International Agency for Research on Cancer (IARC) has not evaluated the carcinogenicity of this chemical.

The American Conference of Governmental Industrial Hygienists (ACGIH) has no listing for this chemical.

The US National Toxicology Program (NTP) has not listed this chemical in its report on carcinogens.

Teratogenicity and Embryotoxicity:
There is no human or animal information available.

Reproductive Toxicity:
There is no human or animal information available.

There is no human or animal in vivo information available. Positive results were obtained in cultured human cells. Negative results were obtained in tests using bacteria.

Toxicologically Synergistic Materials:
There is no information available.

Potential for Accumulation:
No specific information is available. Maleic acid is not expected to accumulate in the body, based on information for related aliphatic carboxylic acids.


Remove source of contamination or move victim to fresh air. Obtain medical attention immediately.

Skin Contact:
Avoid direct contact with this chemical. Wear chemical resistant protective gloves, if necessary. As quickly as possible, flush contaminated area with lukewarm, gently running water for at least 20-30 minutes, by the clock. If irritation persists, repeat flushing. DO NOT INTERRUPT FLUSHING. If necessary, keep emergency vehicle waiting. Under running water, remove contaminated clothing, shoes, and leather goods (e.g., watchbands, belts). Transport victim to an emergency care facility immediately. Discard contaminated clothing, shoes and leather goods.

Eye Contact:
Immediately flush the contaminated eye(s) with lukewarm, gently flowing water for 20-30 minutes, by the clock, while holding the eyelid(s) open. Neutral saline solution may be used as soon as it is available. DO NOT INTERRUPT FLUSHING. If necessary, keep emergency vehicle waiting. Take care not to rinse contaminated water into the non-affected eye or onto the face. If irritation persists, repeat flushing. Quickly transport victim to an emergency care facility.

NEVER give anything by mouth if victim is rapidly losing consciousness, or is unconscious or convulsing. Have victim rinse mouth thoroughly with water. DO NOT INDUCE VOMITING. Have victim drink 240 to 300 mL (8 to 10 oz.) of water to dilute material in the stomach. If vomiting occurs naturally, repeat administration of water. If milk is available, it may be administered AFTER the water has been given. Quickly transport victim to an emergency care facility.

First Aid Comments:
Provide general supportive measures (comfort, warmth, rest).
Consult a doctor and/or the nearest Poison Control Centre for all exposures except minor instances of inhalation or skin contact.
All first aid procedures should be periodically reviewed by a doctor familiar with the material and its conditions of use in the workplace.


Flash Point:
Not applicable.

Lower Flammable (Explosive) Limit (LFL/LEL):
Not applicable

Upper Flammable (Explosive) Limit (UFL/UEL):
Not applicable

Autoignition (Ignition) Temperature:
Not available

Sensitivity to Mechanical Impact:
Probably not sensitive. Stable material.

Combustion and Thermal Decomposition Products:
Carbon dioxide and carbon monoxide.(11) Maleic anhydride may form in fire. Incomplete combustion may also produce acrid smoke and irritating fumes.(10)

Flammable Properties:

Specific Hazards Arising from the Chemical:
During a fire, irritating/toxic gases and fumes may be generated.

Extinguishing Media:
Carbon dioxide, dry chemical powder, alcohol foam, polymer foam, water spray or fog.(11)

Fire Fighting Instructions:
Evacuate area and fight fire from a safe distance or a protected location. Approach fire from upwind to avoid toxic decomposition products.
Water or foam may cause frothing. The frothing may be violent and could endanger personnel close to the fire. However, a water spray or fog that is carefully applied to the surface of the burning material, preferably with a fine spray or fog nozzle, will cause frothing that will blanket and extinguish the fire. In addition, water spray or fog can be used to prevent dust formation, absorb heat, keep containers cool and protect exposed material. Water spray may be used to flush spills away from ignition sources. Solid streams of water may be ineffective and spread material.
The decomposition products of maleic acid may be hazardous to health.
Do not enter without wearing specialized protective equipment suitable for the situation. Firefighter's normal protective clothing (Bunker Gear) will not provide adequate protection. Chemical resistant clothing (e.g., chemical splash suit) and positive pressure self-contained breathing apparatus (MSHA/NIOSH approved or equivalent) may be necessary.


NFPA - Comments:
NFPA has no listing for this chemical in Codes 49 or 325.


Molecular Weight: 116.07

Conversion Factor:
Not applicable

Physical State: Solid
Melting Point: 130-131 deg C (266-267.8 deg F) (crystallized from ethanol and benzene) (13,14); 138-139 deg C (280.4-282.2 deg F) (crystallized from water) (13,14,19)
Boiling Point: Approximately 138 deg C (280.4 deg C) (decomposes) (13)
Relative Density (Specific Gravity): 1.59 at 20 deg C (water = 1) (5,12,13)
Solubility in Water: Very soluble (79 g/100 g) (12,19)
Solubility in Other Liquids: Soluble in ethanol, acetone, methanol, propanol, glacial acetic acid; moderately soluble in diethyl ether; slightly soluble in chloroform; practically insoluble in benzene and carbon tetrachloride (13)
Coefficient of Oil/Water Distribution (Partition Coefficient): Log P(oct) = -0.32 to -0.79 (calculated) (20)
pH Value: 1.47 (0.1M solution) (calculated)
Vapour Density: Not applicable
Vapour Pressure: Very low at normal temperatures. Reported as less than 0.01 kPa (less than 0.076 mm Hg) at 25 deg C.(15)
Saturation Vapour Concentration: Very low at normal temperatures (less than 100 ppm at 25 deg C (calculated))
Evaporation Rate: Probably practically zero at normal temperatures
Critical Temperature: Not available

Other Physical Properties:
ACIDITY: Moderately strong acid; pKa1 = 1.94 (Ka1 = 1.14 X 10(-2)) at 25 deg C; pKa2 = 6.23 (Ka2 = 5.95 X 10(-7) at 25 deg C (12,13)


Normally stable. Above 100 deg C, forms maleic anhydride.(12) Also, converts to fumaric acid slowly at temperatures as low as 100 deg C and readily at 138 deg C (the melting point).(12-14)

Hazardous Polymerization:
Does not occur

Incompatibility - Materials to Avoid:

NOTE: Chemical reactions that could result in a hazardous situation (e.g. generation of flammable or toxic chemicals, fire or detonation) are listed here. Many of these reactions can be done safely if specific control measures (e.g. cooling of the reaction) are in place. Although not intended to be complete, an overview of important reactions involving common chemicals is provided to assist in the development of safe work practices.

STRONG OXIDIZING AGENTS (e.g. perchlorates, peroxides, chromates, sodium hypochlorite) - may react violently or explosively. Increased risk of fire and explosion.(11,15)
ACTIVE METALS (e.g. aluminum, iron, zinc) - react with aqueous solutions of maleic acid to release explosive hydrogen gas.
STRONG BASES (including alkalis such as sodium hydroxide), AMINES or ALKALI METALS - vigorous reaction may occur, yielding heat and pressure. Increased risk of fire.(11,15)
STRONG REDUCING AGENTS (e.g. phosphorus, tin (II) chloride, metal hydrides) - may react vigorously or violently. Increased risk of fire.(11)

Hazardous Decomposition Products:
Information not available

Conditions to Avoid:
Static charge, sparks, heat, other ignition sources, and generation of dust.

Corrosivity to Metals:
Maleic acid in solution is corrosive to metals, such as cast iron and zinc.(10) Acids are generally not corrosive to types 304 and 316 stainless steels, and aluminum is generally resistant to acids at room temperature.(21) Dry maleic acid is not corrosive to metals.(10)


LC50 (rat): Greater than 720 mg/m3 (0-15 minute exposure) (1)

LD50 (oral, rat): 708 mg/kg (1)
LD50 (oral, mouse): 3000 mg/kg; cited as 60 mg (2)

LD50 (dermal, rabbit): 1560 mg/kg (1)

Eye Irritation:

Permanent damage (opacity and vascularization) was observed in rabbits following application of a 10% solution (pH 1) for 30 seconds.(3) Cloudiness of the cornea, redness and swelling, which healed within 1 day, was observed in rabbits following application of a 1% solution for 2 minutes. A similar effect, which healed after 6-7 days, was observed following application of a 5% solution. Cloudiness of the cornea and pain was observed following application of maleic acid in powdered form. Swelling and redness were observed after 2 days and the eyes returned to normal within a few days.(4) Severe irritation (scored 95/110) was observed in rabbits following application of dry powder in a standard Draize test.(1)

Skin Irritation:

Mild irritation (scored 1.5/8) was observed following application of maleic acid, moistened with water, to rabbits in a standard Draize test.(1) In another study, moderate irritation was observed in guinea pigs and mild irritation in rabbits.(5, unconfirmed)

Effects of Short-Term (Acute) Exposure:

Inactivity, an increased breathing rate and sedation were observed in rats within 15 minutes following a 1-hour exposure to a very high airborne concentration (0.72 mg/L (720 mg/m3)). No deaths occurred due to exposure. No visible toxic effects were observed at autopsy.(5, unconfirmed)

Kidney injury was observed in rats following one-time oral administration of 200 or 400 mg/kg. Tissue death (necrosis) was observed after 24 hours at both dose levels.(6)

Effects of Long-Term (Chronic) Exposure:

A decreased growth rate was observed in rats fed 1% or more in the diet for 1 year (equivalent to about 500 mg/kg/day). After 2 years, the mortality was significantly increased in those fed 0.5%, 1.0% or 1.5% (approximately 250-750 mg/kg/day) in the diet. Slight changes in kidney tissues and shrinking (atrophy) of the liver and testes were observed at 1.5%.(7)


Selected Bibliography:
(1) Anonymous. Maleic acid. Industrial Bio-test Laboratories, Inc., Data Sheet No 7-4/70. 1970. (NIOSHTIC Control no. 00066072)
(2) Boyland, E. Experiments on the chemotherapy of cancer. 4. Further experiments with aldehydes and their derivatives. Biochemical Journal. Vol. 34 (1940). p. 1196-1201
(3) Grant, W.M., et al. Toxicology of the eye. 4th edition. Charles C. Thomas, 1993. p. 917-918
(4) Winter, C.A., et al. The irritating effects of maleic acid and of maleic anhydride upon the eyes of rabbits. American Journal of Ophthalmology. Vol. 33 (March, 1950). p. 387-388
(5) Katz, G.V., et al. Aliphatic carboxylic acids. In: Patty's industrial hygiene and toxicology. 4th edition. Edited by G.D. Clayton et al. Volume II. Toxicology. Part E. John Wiley and Sons, 1994. p. 3637-3640
(6) Verani, R.R., et al. Proximal tubular necrosis associated with maleic acid administration to the rat. Laboratory Investigation. Vol. 46, no. 1 (1982). p. 79-88
(7) Fitzhugh, O.G., et al. The comparative chronic toxicities of fumaric, tartaric, oxalic, and maleic acids. Journal of the American Pharmaceutical Association. Vol. 36, no. 7 (July, 1947). p. 217-219
(8) RTECS record for maleic acid. Last updated: 9704
(9) Lake, R.S., et al. Nonmutagenicity of maleic acid and its sodium salts in Salmonella assays. Mutation Research. Vol. 207, no. 1 (January, 1988). p. 1-5
(10) HSDB record for maleic acid. Last revision date: 97/04/01
(11) The Sigma-Aldrich library of chemical safety data. Edition II. Volume 2. Sigma-Aldrich Corporation, 1988. p. 2183A
(12) Lohbeck, K., et al. Maleic and fumaric acids. In: Ullmann's encyclopedia of industrial chemistry. 5th completely revised edition. Volume A 16. VCH Verlagsgesellschaft, 1990. p. 53-62
(13) Felthouse, T.R., et al. Maleic anhydride, maleic acid, and fumaric acid. In: Kirk-Othmer encyclopedia of chemical technology. 4th edition. Volume 15. John Wiley and Sons, 1995. p. 893-928
(14) Budavari, S, ed. The Merck index: an encyclopedia of chemicals, drugs, and biologicals. 12th edition. Merck and Co., Inc., 1996. p. 973
(15) Chemical safety sheets: working safely with hazardous chemicals. Kluwer Academic Publishers, 1991. p. 545
(16) Dust explosions in factories. Health and Safety Executive, 1975
(17) Grossel, S.S. Safety considerations in conveying of bulk solids and powders. Journal of Loss Prevention in the Process Industries. Vol. 1 (April, 1988). p. 62-74
(18) Schwab, R.F. Dusts. In: Fire protection handbook. Edited by A.E Cote. 18th edition. National Fire Protection Association, 1991. p. 4-174 to 4-181
(19) Dean, J.A. Lange's handbook of chemistry. 14th edition. McGraw-Hill, Inc., 1992. p. 1.238
(20) Leo, A., et al. Partition coefficients and their uses. Chemical Reviews. Vol. 71, no. 6 (December, 1971). p. 562
(21) Elder, G.B. Materials of construction for organic acids. In: Process industries corrosion: the theory and practice. Edited by B.J. Moniz, et al. National Association of Corrosion Engineers, 1986. p. 287-296
(22) Forsberg, K., et al. Quick selection guide to chemical protective clothing. 4th ed. Van Nostrand Reinhold, 2002
(23) European Economic Community. Commission Directive 93/72/EEC. September 1, 1993

Information on chemicals reviewed in the CHEMINFO database is drawn from a number of publicly available sources. A list of general references used to compile CHEMINFO records is available in the database Help.

Review/Preparation Date: 1997-12-24

Revision Indicators:
TDG 2002-12-17
UN/NA No 2002-12-17
US transport 2002-12-17
Resistance of materials for PPE 2004-04-06
Bibliography 2004-04-06
Flash point 2006-10-05
LFL/LEL 2006-10-05
UFL/UEL 2006-10-05

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