Maleic acid was first obtained almost 200 years ago. She was able to synthesize by distillation of malic acid. In the future, it found its application in the chemical field, and this is worth telling in detail. However, first we will talk about its properties and other features.
General characteristics
The formula of maleic acid is as follows: NOOS-CH = CH-COOH (or H 4 C 4 O 4 ). This substance is an organic compound with two bases. According to the IUPAC nomenclature, it is correctly called cis-butenedioic acid.
The characteristics of this substance can be distinguished in the following list:
· The molar mass is 116.07 g / mol.
· The density is 1.59 g / cm³.
· Melting and decomposition temperature reaches 135 ° C. Flash occurs at 127 ° C.
· The solubility in water is 78.8 g / l. This process is best carried out at 25 ° C.
This substance has a trans isomer, and it is known as fumaric acid. Its molecules are more stable than maleic. Hence the difference in the values of the 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 because hydrogen bonds are formed in maleic molecules.
Receiving a substance
The production of maleic acid is carried out by hydrolysis of anhydride C 4 H 2 O 3 . It is an organic compound having a solid consistency in the 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.
Anhydride itself was previously synthesized by the oxidation of benzene or other aromatic compounds. Now this method is rarely used. Due to increased prices for benzene and the environmental impact of this substance, it was replaced with n-butane, a hydrocarbon of the alkane class.
Reaction entry
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 basic substance. Malic acid is known as a food supplement under the designation E296. It is of natural origin, so it is used in confectionery and in the production of fruit waters. It is also applicable in medicine.
The maleic compound can also be converted to succinic acid, which is used to stimulate plant growth and increase yield. 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 (by splitting water from molecules), maleic anhydride can be obtained from it.
All of these reactions could theoretically be used in industry for the production of these substances. That's just they are economically disadvantageous, so they do not resort to them.
Application
It is difficult to overestimate the properties of maleic acid. It itself is used only to obtain a fumar compound, but the use of its derivatives is widespread:
· Anhydride is involved in the manufacture of polyester products. Pitches in particular. End products are actively used in the construction industry. These are paintwork materials, artificial stone, fiberglass, etc.
· Reagents are used for the manufacture of alkyd resins that perfectly harden oil-based coatings. They are also used as anti-corrosion coatings.
· Also from anhydride, since it is a copolymer of maleic acid, make synthetic fabrics and artificial fibers.
· The esters of this substance are used as solvents. The most common is diethyl maleate. It is used by chemical laboratories, defense enterprises, as well as in the field of paint and varnish products.
· Maleic hydrazide is used as a herbicide. It perfectly affects weeds.
Obtaining fumaric acid
A few words must also be said about him. To obtain fumaric acid, maleic is catalytically isomerized. This process is carried out using thiourea (thiocarbamide). Although it is often replaced by inorganic acids.
Since the fumar compound is poorly soluble, it is easy to separate it from the maleic substance. Both acids belong to 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 disadvantageous from an energy point of view.
So, the industry uses the method already mentioned earlier - catalytic isomerization of maleic compounds in water.
The use of fumar compounds
This is worth mentioning in the end. Fumaric acid is the longest used in the food industry. It was first used in 1946. This compound has a fruity taste, so it is often used as a sweetener. It is designated E297.
Fumaric acid is often replaced with tartaric and citric. It is cost effective. If you add citrate, then to achieve the desired taste effect, you need 1.36 g. Fumarate needs less - only 0.91 g.
Also, the esters of this substance are used in the treatment of a skin disease such as psoriasis. For an adult, a daily norm of 60-105 milligrams is established (the exact dose depends on the individual case). May be increased over time to 1300 mg per day.
And the salt of this substance is a key component of such drugs as Confumin and Methusol. The first helps the body adapt to a 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.