Maleic acid
[CAS# 110-16-7]

Identification

• Classification: Organic raw materials >> Carboxylic compounds and derivatives >> Acyclic carboxylic acid
• Name: Maleic acid
• Synonyms: cis-Butenedioic acid
• Molecular Formula: C₄H₄O₄
• Molecular Weight: 116.07
• CAS Registry Number: 110-16-7
• EC Number: 203-742-5
• SMILES: C(=CC(=O)O)C(=O)O

Properties

• Density: 1.59
• Index of Refraction: 1.549, Calc.^*
• Melting point: 134-138 °C
• Flash point: 127 °C
• Water solubility: 790 g/L (25 °C)

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS05;GHS07 Danger
• Risk Statements: H302-H335-H315-H319-H317
• Safety Statements: P234-P260-P264-P264+P265-P280-P301+P330+P331-P302+P361+P354-P304+P340-P305+P351+P338-P305+P354+P338-P316-P317-P321-P337+P317-P363-P390-P405-P406-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	4	H302
Skin sensitization	Skin Sens.	1	H317
Specific target organ toxicity - single exposure	STOT SE	3	H335
Skin irritation	Skin Irrit.	2	H315
Eye irritation	Eye Irrit.	2	H319
Acute toxicity	Acute Tox.	4	H312
Serious eye damage	Eye Dam.	1	H318
Skin corrosion	Skin Corr.	1B	H314
Specific target organ toxicity - single exposure	STOT SE	3	H370
Skin sensitization	Skin Sens.	1B	H317
Acute toxicity	Acute Tox.	3	H301
Specific target organ toxicity - repeated exposure	STOT RE	2	H373
Chronic hazardous to the aquatic environment	Aquatic Chronic	3	H412
Chronic hazardous to the aquatic environment	Aquatic Chronic	2	H411
Acute toxicity	Acute Tox.	4	H332
Eye irritation	Eye Irrit.	2	H318
Skin sensitization	Skin Sens.	1A	H317
Eye irritation	Eye Irrit.	2A	H319
Substances or mixtures corrosive to metals	Met. Corr.	1	H290
Skin corrosion	Skin Corr.	1C	H314

• Transport Information: UN 2215

Discovery and Applications

Maleic acid, a dicarboxylic acid with the molecular formula C4H4O4, was first identified in the early 19th century during studies on the distillation of malic acid, which is found naturally in various fruits. Its discovery marked a significant development in organic chemistry, as maleic acid exhibits isomerism with fumaric acid, a structural variation of the same molecular formula but differing in the spatial arrangement of the carboxyl groups. This distinction in structure makes maleic acid particularly reactive and valuable in numerous chemical applications.

Maleic acid exists in a cis-configuration, with both carboxyl groups (-COOH) situated on the same side of the carbon-carbon double bond. This structure grants it higher solubility in water and reactivity compared to its trans-isomer, fumaric acid. The discovery of maleic acid and its ability to isomerize into fumaric acid under heat or in the presence of catalysts broadened its industrial significance.

The applications of maleic acid are widespread, particularly in the production of resins and polymers. One of its primary uses is in the manufacture of unsaturated polyester resins, where maleic acid acts as a key monomer. These resins are essential in the production of fiberglass-reinforced plastics, which are used in automotive, marine, and construction industries. Additionally, maleic acid is utilized in the synthesis of alkyd resins, which find applications in coatings, paints, and varnishes.

Maleic acid’s reactivity makes it a versatile chemical intermediate in various industrial processes. It is a precursor in the production of maleic anhydride, a compound that plays a critical role in the manufacture of synthetic resins, plasticizers, and agricultural chemicals. Maleic acid also contributes to the production of fumaric acid through isomerization, where its conversion is valuable in food additives, pharmaceuticals, and industrial processes.

In the food industry, maleic acid serves as a flavor enhancer and acidulant in processed foods, beverages, and confectionery. Its sharp, tart flavor is ideal for regulating acidity in food products. Furthermore, its derivatives, such as maleates, are used in pharmaceuticals to improve the solubility and bioavailability of drugs.

Maleic acid also finds applications in water treatment, where it acts as a sequestering agent, preventing the formation of scale and mineral deposits. In agriculture, maleic acid derivatives are employed as plant growth regulators and herbicides, helping to control unwanted vegetation and enhance crop production.

As maleic acid continues to be produced via sustainable and efficient methods, its industrial importance remains significant. Advances in green chemistry are also exploring bio-based routes for maleic acid production, making it a promising candidate for renewable chemical platforms.

References

2003. Reversible and irreversible inhibitory activity of succinic and maleic acid derivatives on acetylcholinesterase. European journal of pharmaceutical sciences : official journal of the European Federation for Pharmaceutical Sciences.
DOI: 10.1016/s0928-0987(03)00023-x

2010. Evaluation of the Effect of Maleic Acid and Ethylenediaminetetraacetic Acid on the Microhardness and Surface Roughness of Human Root Canal Dentin. Journal of Endodontics.
DOI: 10.1016/j.joen.2010.04.002

2024. Novel Gold Nanoparticle-Based Plasmonic Sensor for Maleic Acid. Plasmonics.
DOI: 10.1007/s11468-024-02681-y