Name | Maleic acid |
CAS number | 25389-94-0 |
Description | Maleic acid is a colorless crystalline solid having a faint odor. It is combustible though it may take some effort to ignite. It is soluble in water. It is used to make other chemicals and for dyeing and finishing naturally occurring fibers. |
Appearance | Solid powder |
Quality Standard | USP, EP, BP, CP |
Shipping Condition | Shipped under ambient temperature as non-hazardous chemical. This product is stable enough for a few weeks during ordinary shipping and time spent in Customs. |
Storage Condition | Dry, dark and at 0 - 4 ℃ for short term (days to weeks) or -20 ℃ for long term (months to years). |
Shelf Life | >2 years if stored properly |
Sample package | Aluminium foil bag |
Commercial package | Aluminium Tin, Fiber drum |
Origin | China |
Maleic acid More Info
Maleic acid, also known as cis-butenedioic acid, is a vital organic compound belonging to the dicarboxylic acid family. It is widely recognized as the cis-isomeric form of butenedioic acid, with fumaric acid being its trans-isomer. This compound plays a pivotal role as a chemical intermediate in numerous industrial sectors due to its unique structural and chemical properties.
1. Basic Information
- Chemical Name: Maleic acid; cis-Butenedioic acid
- CAS Number: 110-16-7
- Molecular Formula: C₄H₄O₄
- Molecular Weight: 116.07 g/mol
- Structural Formula: HOOC-CH=CH-COOH (cis configuration)
2. Physical and Chemical Properties
2.1 Physical Properties
- Appearance: Colorless or white crystalline powder with a faint pungent acidic odor
- Melting Point: 135–139 °C (decomposes at boiling point, undergoing isomerization to fumaric acid)
- Density: 1.59 g/cm³ (at 20 °C)
- Solubility: Highly soluble in water (78.8 g/100 mL at 25 °C), ethanol, and acetone; slightly soluble in benzene and toluene; insoluble in petroleum ether
- pH Value: Approximately 1.5 (1% aqueous solution at 25 °C)
2.2 Chemical Properties
- Acidity: As a dicarboxylic acid, it has two dissociable hydrogen ions (pKa₁ = 1.92, pKa₂ = 6.23 at 25 °C), exhibiting stronger acidity than its trans-isomer fumaric acid due to the intramolecular hydrogen bonding in its cis configuration.
- Isomerization: Easily converts to fumaric acid (trans-butenedioic acid) when heated above its melting point or under the action of strong acids, light, or catalysts. This isomerization is irreversible under normal conditions.
- Addition Reactions: The carbon-carbon double bond in its structure undergoes typical addition reactions, such as addition with bromine to form dibromosuccinic acid, and addition with water under acidic conditions to form malic acid.
- Polymerization Reactions: Can participate in copolymerization reactions with other monomers (e.g., styrene, vinyl acetate) to form polymers with specific properties, such as unsaturated polyester resins.
- Esterification Reactions: Reacts with alcohols to form maleic acid esters, which are important raw materials for plasticizers and lubricants.
3. Preparation Methods
The industrial production of maleic acid mainly relies on the catalytic oxidation of benzene or butane, with the benzene oxidation method being the most commonly used process:
1. Benzene Oxidation Method: Benzene reacts with oxygen in the presence of a vanadium-titanium catalyst at a temperature of 350–450 °C and a pressure of 0.3–0.5 MPa to produce maleic anhydride. Maleic acid is then obtained by hydrolyzing maleic anhydride with water. This method has the advantages of mature technology and high yield.
2. Butane Oxidation Method: N-butane is oxidized with air or oxygen under the catalysis of a vanadium-phosphorus oxide (VPO) catalyst at 300–400 °C to generate maleic anhydride, which is subsequently hydrolyzed to maleic acid. This method is more environmentally friendly and cost-effective as butane is a cheaper raw material compared to benzene, and it produces fewer by-products.
3. Other Methods: Small-scale production can be achieved through the oxidation of furfural or the isomerization of fumaric acid, but these methods are rarely used in industrial mass production due to low efficiency and high costs.
4. Main Applications
Maleic acid is a versatile chemical intermediate with extensive applications in various industries, including:
4.1 Polymer and Resin Industry
It is a key raw material for the production of unsaturated polyester resins (UPR), which are widely used in fiberglass-reinforced plastics (FRP) for manufacturing boats, automotive parts, pipes, and construction materials. Additionally, maleic acid is used in the synthesis of alkyd resins, which are employed in coatings and paints due to their excellent adhesion and weather resistance.
4.2 Agrochemical Industry
Maleic acid serves as an intermediate in the synthesis of various pesticides and herbicides, such as glyphosate, malathion, and carbaryl. It is also used in the production of plant growth regulators to promote crop growth and improve yield.
4.3 Surfactant and Detergent Industry
It is used in the preparation of anionic surfactants, such as maleic acid monoalkyl esters and sulfosuccinic acid esters, which are widely used in detergents, shampoos, and industrial cleaning agents due to their excellent foaming, emulsifying, and cleaning properties.
4.4 Pharmaceutical and Food Industry
In the pharmaceutical industry, maleic acid is used as an intermediate in the synthesis of active pharmaceutical ingredients (APIs), such as antihistamines, antibiotics, and anti-inflammatory drugs. In the food industry, although fumaric acid is more commonly used as an acidulant, maleic acid is occasionally used in the production of artificial sweeteners, flavor enhancers, and food preservatives (with strict dosage limits due to its potential irritancy).
4.5 Other Applications
Maleic acid is used in the production of lubricant additives to improve the anti-wear and anti-oxidation properties of lubricants. It is also employed in water treatment as a chelating agent to remove metal ions from water. Furthermore, it is used in the textile industry for dyeing and finishing processes to enhance the color fastness of fabrics.
5. Safety, Handling, and Storage
5.1 Safety Hazards
Maleic acid is corrosive to the skin, eyes, and respiratory tract. Direct contact can cause redness, irritation, and burns. Inhalation of its dust or vapor may lead to coughing, chest tightness, and respiratory tract inflammation. Ingestion can cause abdominal pain, nausea, vomiting, and diarrhea. It is not classified as a flammable substance, but it can react with strong oxidizing agents to produce harmful gases.
5.2 Handling Precautions
When handling maleic acid, operators should wear appropriate personal protective equipment (PPE), including chemical-resistant gloves, goggles, a face mask, and a protective gown. Avoid direct contact with skin and eyes, and ensure good ventilation in the working area. In case of contact with skin or eyes, immediately rinse with plenty of water for at least 15 minutes and seek medical attention if necessary. If inhaled, move the victim to a well-ventilated area and provide oxygen if needed. In case of ingestion, do not induce vomiting and seek immediate medical help.
5.3 Storage Conditions
Store maleic acid in a cool, dry, and well-ventilated warehouse. Keep it away from incompatible substances, such as strong oxidizing agents, bases, and metals. The storage area should be equipped with appropriate fire-fighting equipment and leakage handling materials. The product should be stored in sealed containers (e.g., 25kg paper bags with PE liners, 500kg/1000kg jumbo bags) to prevent moisture absorption, dust generation, and contamination. The shelf life is typically 12 months when stored under proper conditions.
6. Environmental Impact
Maleic acid is biodegradable in the environment. Under aerobic conditions, it can be decomposed by microorganisms into carbon dioxide and water. However, large-scale leakage or improper disposal can cause acidification of soil and water bodies, affecting aquatic and terrestrial organisms. Therefore, waste maleic acid and its wastewater should be treated according to relevant environmental regulations before discharge. Solid waste should be disposed of in designated landfills or incinerated in accordance with local laws.
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