Maleic acid was first discovered almost 200 years ago. It was synthesized by distillation of malic acid. In the future, it found its application in the chemical field, and this is worth talking about in detail. However, first we will talk about its properties and other features.
General Features
The formula for maleic acid looks like this: HOOC-CH=CH-COOH (or H4C4O4). This substance is an organic compound with two bases. According to IUPAC nomenclature, it is properly called cis-butenedioic acid.
The characteristics of this substance can be identified in the following list:
The molar mass is 116.07 g/mol.
Density is 1.59 g/cm³.
· The melting and decomposition temperature reaches 135 °C. Flash occurs at 127°C.
· Water solubility index is 78.8 g/l. This process works best at 25°C.
This substance has a trans isomer, and itknown as fumaric acid. Its molecules are more stable than those of maleic. Hence the difference in combustion temperature, which is 22.7 kJ/mol.
And fumaric acid, unlike maleic acid, is very poorly soluble in water. Only 6.3 g/l. This is due to the fact that a hydrogen bond is formed in maleic molecules.
Getting substance
Maleic acid is produced by hydrolysis of anhydride C4H2O3. It is an organic compound that has a solid consistency in its pure state. This substance is usually colorless or white.
Anhydride has very diverse chemical properties, because it has an extremely high reactivity and two functional groups. Maleic acid is formed due to its interaction with water. But if you combine it with alcohols, you get incomplete esters.
The anhydride itself was previously synthesized by the oxidation of benzene or other aromatic compounds. Now this method is rarely used. Due to the rise in prices for benzene and the impact of this substance on the environment, it was replaced by n-butane, a hydrocarbon of the alkane class.
Entry into reactions
It is worth noting that maleic acid can actually be turned into malic acid. This is achieved through hydration - the addition of water molecules to the ions / particles of the main substance. Malic acid is known as a food additive under the designation E296. It has a natural origin, so it is used inconfectionery and in the production of fruit waters. It is also applicable in medicine.
Also, the maleic compound can be converted into succinic acid, which is used to stimulate plant growth and increase yields. It was first obtained in the 17th century by distillation of amber. And now this substance is synthesized by hydrogenation of maleic acid. That is, by adding hydrogen to it. And through dehydration (cleavage of water from molecules), maleic anhydride can be obtained from it.
All of the listed reactions could theoretically be used in industry for the production of these substances. But they are not economically viable, so they are not resorted to.
Application
It is difficult to overestimate the properties of maleic acid. It itself is used only to obtain a fumaric compound, but the use of its derivatives is widespread:
· The anhydride is used in the manufacture of polyester products. Small, in particular. End products are actively used in the construction industry. These are paintwork materials, artificial stone, fiberglass, etc.
· Reagents are used to make alkyd resins, which are excellent hardeners for oil-based coatings. They are also used as an anti-corrosion coating.
Anhydride is also used as a copolymer of maleic acid to make synthetic fabrics and artificial fibers.
· Ethers of this substance are used as solvents. The most common is diethyl maleate. Hisused by chemistry labs, defense industry, and the paint and varnish industry.
· The maleic compound hydrazite is used as a herbicide. It is excellent at killing weeds.
Production of fumaric acid
It is also necessary to say a few words about him. To obtain fumaric acid, maleic acid is catalytically isomerized. This process is carried out using thiourea (thiocarbamide). Although it is often replaced with inorganic acids.
Since the fumaric compound is poorly soluble, it is easy to isolate it from the maleic substance. Both acids are conformers - they have the same number of atoms and molecules, as well as a similar structure. But, despite this, they cannot turn into each other spontaneously. For this process to occur, it is necessary to break the carbon double bond, but this is unfavorable from an energy point of view.
So the industry uses the method already mentioned earlier - the catalytic isomerization of a maleic compound in water.
Use of fumaric compound
This is worth talking about in the end. The longest use of fumaric acid is in the food industry. It was first used in 1946. This compound has a fruity taste, which is why it is often used as a sweetener. Designated E297.
Fumaric acid is also often replaced with tartaric and citric acid. It's cost effective. If you add citrate, then to achieve the desired1.36 g of fumarate is needed for the taste effect. Less fumarate is needed - only 0.91 g.
Ethers of this substance are also used in the treatment of skin diseases such as psoriasis. For an adult, the daily norm is 60-105 milligrams (the exact dose depends on the individual case). May be increased over time to 1300 mg daily.
And the s alt of this substance is a key component of drugs such as Konfumin and Mafusol. The first helps the body adapt to the lack of oxygen and regulates metabolism. And the second improves the rheological properties of blood and its viscosity.
Interestingly, even the human body is able to synthesize fumarate. It is formed by the skin when it is exposed to sunlight. In addition, fumarate is a by-product of the urea cycle.
