MALEIC ACID: STRUCTURE, PROPERTIES, PRODUCTION, USES - CHEMISTRY - 2025

The maleic acid is an organic acid compound whose chemical formula is HOOC-CH = CH-COOH. It is a dicarboxylic acid. It is also known as cis -butenedioic acid, maleinic acid, maleic acid, and toxilic acid.

Maleic acid is found naturally in tobacco, ginseng, and beverages such as beer and wine. It is also found in cigarette smoke and car exhaust.

Maleic acid. Ninomy. Source: Wikipedia Commons.

Its double bond and the two –COOH groups make it susceptible to various chemical reactions, which is why it is used to synthesize many other compounds, materials and products.

It is also of great help for the processing of textiles such as cotton, wool and silk. It allows to obtain glues, resins and synthetic oils. It is used to prevent the oxidation of fats and oils. In turn, many of its derivatives are used in medical and veterinary applications.

According to some research it is one of the components of fermented beverages that stimulates gastric acid secretion.

Structure

The maleic acid molecule is made up of a skeleton of 4 carbon atoms, of which the two ends form carboxyl -COOH groups and the two central ones form a C = C double bond.

The -COOH groups are located cis with respect to the double bond. The oxygens and hydrogens of -COOH are accommodated in such a way that a hydrogen is located between the oxygens.

Structure of maleic acid. Benjah-bmm27. Source: Wikipedia Commons.

Nomenclature

- Maleic acid

- cis -butenedioic acid

- Toxilic acid

- Maleinic acid

- Maleic acid

Properties

Physical state

Colorless crystalline solid, monoclinic crystals.

Maleic acid crystals. LHcheM. Source: Wikipedia Commons.

Molecular weight

116.07 g / mol

Melting point

130.5 ºC

Boiling point

135 ºC (decomposes)

Specific weight

1,609

Solubility

Very soluble in water: 79 g / 100 g H ₂ O at 20 ºC

Dissociation constants

K ₁ = 1000 x 10 ^-5

K ₂ = 0.055 x 10 ^-5

Chemical properties

Maleic acid has two -COOH groups and a central C = C double bond as reactive sites.

Its anhydride is a 5-atom cyclic molecule, whose products are unstable towards hydrolysis, especially the reaction products with amino -NH ₂ groups.

This makes it serve as a reversible blocker of -NH ₂ groups to temporarily mask them and prevent them from reacting when other reactions are taking place.

This is useful for multiple purposes, especially to modify proteins at the laboratory level.

Obtaining

Industrially, it is obtained by the catalytic oxidation of benzene in the presence of vanadium pentoxide.

Also by oxidation of n-butane or n-butylene in the vapor phase with air, in the presence of a solid catalyst.

It can also be obtained by the hydrolysis of maleic anhydride.

It is also obtained as a by-product during the manufacture of phthalic anhydride starting from naphthalene.

Maleic acid uses

In the production of other chemical compounds

Maleic acid allows many other chemical compounds to be obtained. It is used in the synthesis of aspartic, malic, tartaric, succinic, lactic, malonic, propionic and acrylic acid.

As a chemical intermediate, maleic acid finds use in almost all fields of industrial chemistry.

In various applications

Maleic acid makes it possible to obtain synthetic glues, colorants, alkyd resins and synthetic oils.

Its derivatives, the maleate salts, are used in antihistamine formulations and similar drugs.

It is used as a preservative in fats and oils as it serves to delay the appearance of rancidity.

It is used in corrosion inhibitors and antifouling products. It also works as an agent to regulate the pH.

In the textile industry

It is used in the processing of wool, silk and cotton.

The obtaining of oligomers (polymers of few units) of maleic acid has been investigated to use them as a finishing agent in obtaining permanent press cotton, so as not to use formaldehyde polymers.

In this case, the polymerization of maleic acid is carried out in an aqueous medium in the presence of NaH ₂ PO ₂ and a radical initiator such as Na ₂ S ₂ O ₈. The maleic acid oligomer has carboxyl groups –COOH attached to the adjacent –CH ₂ - of its molecular backbone.

It is applied to cotton fabric as a network-forming agent and the curing process is carried out.

In this way the maleic acid oligomer is effective in crosslinking cotton cellulose and imparting high levels of wrinkle resistance to cotton fabrics.

Furthermore, the fabrics treated with maleic acid polymers did not show yellowing and showed greater retention of strength or resistance than those treated with formaldehyde polymers.

Author: Steve Buissinne. Source: Pixabay.

In medicine

There are various compounds based on maleic acid that are used in the treatment of cancer.

Sunitinib maleate (Sutent) is an anticancer drug that works in several ways to inhibit the proliferation of tumor cells and angiogenesis.

It is approved for the treatment of renal cell carcinoma and drug-resistant gastrointestinal tumor. Its activity is being investigated in hepatocellular carcinoma and lung cell cancer. It is supplied orally in capsules.

Sunitinib molecule. Fvasconcellos (talk · contribs). Source: Wikipedia Commons.

According to a study carried out in 2015, nanoparticles were prepared with a styrene-maleic acid copolymer to which the drug Paclitaxel used for the treatment of cancer was attached via an ester bond.

These nanoparticles showed greater retention in plasma and in the tumor, inhibiting the growth of the latter with an improvement in the apoptosis effect (death) of cancer cells.

They did not show toxicity in the main organs, tissues and hematological system.

For these reasons they are proposed as an alternative drug delivery or delivery system in solid tumors.

In dentistry

According to some research, maleic acid 10% reduces mineral loss from teeth when applied in dental treatments.

It is used to gently erode the tooth surface and thus promote the adhesion of other materials.

It is reported that it can produce bonding or adhesion forces equal to that with 37% orthophosphoric acid.

In veterinary medicine

Accepromazine maleate is used as a tranquilizer in veterinary medicine for sedation of animals prior to anesthesia. This compound protects against arrhythmia-generating effects of anesthesia.

Author: Arvydas Lakacauskas. Source: Pixabay.

Potential use as a disinfectant

It has recently been found (2018) that maleic acid can inhibit the resistance of the bacterium Listeria monocytogenes to acids, making it susceptible to the action of these when they are used to disinfect in food industries.

It is believed that it acts on an enzyme that favors the resistance of these microorganisms to acids, deactivating it. Maleic acid has also been found to remove biofilms from such bacteria.

These characteristics make it a potential candidate for equipment disinfection in the food industry.

Effects of maleic acid contained in fermented beverages such as beer and wine

Studies conducted with humans ingesting fermented glucose solutions found that dicarboxylic acids such as maleic acid are powerful stimulants of gastric acid.

According to the researchers, this is most likely to occur in fermented beverages such as beer, champagne and wine, but not in distilled alcoholic beverages such as whiskey and cognac.

This is because the stimulating effect of gastric acid is caused by dicarboxylic acids such as maleic acid and not by alcohol (ethanol).

Risks

Contact of maleic acid with the eyes or skin causes irritation and can lead to dermatitis on prolonged contact. Its inhalation produces nose and throat irritation. It can have a harmful effect on the kidneys.

When exposed to heat or flame, its combustion occurs and the gases or fumes produced cause irritation.

If maleic acid is released, the environment is expected to be broken down or decomposed by microorganisms. It does not accumulate in aquatic organisms.

References

1. US National Library of Medicine. (2019). Maleic Acid. Recovered from: pubchem.ncbi.nlm.nih.gov.
2. Hermanson, GT (2013). Functional Targets for Bioconjugation. In Bioconjugate Techniques (Third Edition). Recovered from sciencedirect.com.
3. Teyssen, S. et al. (1999). Maleic acid and succinic acid in fermented alcoholic beverages are the stimulants of gastric acid secretion. J. Clin. Invest. 1999; 103 (5): 707-713. Recovered from jci.org.
4. Flecknell, P. et al. (2015). Preanesthesia, Anesthesia, Analgesia, and Euthanasia. In Laboratory Animal Medicine (Third Edition). Recovered from sciencedirect.com.
5. Chen, D. et al. (2005). Aqueous Polymerization of Maleic Acid and Cross-Linking of Cotton Cellulose by Poly (maleic Acid). Ind. Eng. Chem. Res. 2005, 44, 7921-7927. Recovered from pubs.acs.org.
6. Carver, JR (2011). Management of cardiac and pulmonary treatment-related side effects. In Supportive Oncology. Recovered from sciencedirect.com.
7. SerdarÜsümez, NejatErverdi. (2010). Adhesives and Bonding in Orthodontics. In Current Therapy in Orthodontics. Recovered from sciencedirect.com.
8. Dalela, M. et al. (2015). pH-Sensitive Biocompatible Nanoparticles of Paclitaxel-Conjugated Poly (styrene-co-maleic acid) for Anticancer Drug Delivery in Solid Tumors of Syngeneic Mice. ACS Appl Mater Interfaces. 2015 Dec 9; 7 (48): 26530-48. Recovered from ncbi.nlm.nih.gov.
9. Paudyal, R. et al. (2018). A novel approach in acidic disinfection through inhibition of acid resistant mechanisms; Maleic acid-mediated inhibition of glutamate decarboxylase activity enhances acid sensitivity of Listeria monocytogenes. Food Mycrobiol. 2018 Feb. 69: 96-104. Recovered from ncbi.nlm.nih.gov.