Benzene: physical properties and chemical, structure and description
One of the representatives of aromatic hydrocarbons is benzene. The structure, physical properties of this substance are presented in this article.
The benzene compound was discovered before allarenas. Michael Faraday brought it out by distillation of crystals of glowing gas. Another way is to decompose the whale oil under the influence of high temperatures. Another scientist, namely, Mitchellich, in 1834 received benzene, the physical properties of which were not studied at that time, with the help of dry distillation of the same name with the addition of lime.
The scientist proposed the name "gasoline" for thissubstance. However, a person investigating the properties and composition of benzene gave him the name customary for modern people. In translation from the German language "Ol" means "oil". At present, the name of the substance does not change, since the suffix -ol corresponds to the class of alcohols. In 1860 Kenule identified a new group of compounds, namely - aromatic substances, because they had a pleasant smell.
There is such a thing as "raw benzene". Physical properties and application directly depend on the composition of the substance. Thus, benzene contains a large number of substances, for example, pyridine, coumarones, cumene, even naphthalene. To turn the crude product into pure, benzene is purified and its rectification is carried out.
Cleaning is done as follows: the substance is washed successively in an alkali solution, in an acid and in water. To remove bases and phenols from the crude product, it is first purified with sulfuric acid.
The substance was first recorded as an incorrect formula, which looked like C2H2.
Michael Faraday made a mistake, because at that time the atomic mass of carbon was taken for 6 amu. Another scientist, called Mitcherlich, wrote down the formula correctly - C6H6.
Like other hydrocarbons, benzene formshomological series. The simplest of its homologues is a substance called methylbenzene. Its technical name is toluene. It is a liquid that lacks color, but has a characteristic smell. The physical and chemical properties of benzene and methylbenzene are similar.
The substance is extracted together with benzene, then it is separated by fractional distillation. Most often, toluene is used to produce explosives, especially TNT.
There are the following physical properties of benzene and its homologues:
- The substances are in a liquid aggregate state. Benzene boils at a temperature of 80.1 degrees Celsius. In the frozen state it turns into a crystalline mass of white color. The compound solidifies at a temperature of 5.5 degrees.
- Benzene is a non-polar substance that does notdissolves in water. At the same time, a mixture is formed, whose boiling point is 69.25 degrees. Its composition does not change when passing from one aggregate state to another. The compound is mixed with most non-polar solvents.
These were the basic physical properties of benzene. The table in which all the information about them is indicated, of course, will be much more.
With the participation of benzene in most cases, there are substitution reactions, but there are also reactions of addition or oxidation.
In addition reactions, the substance appears inas an unsaturated hydrocarbon. If there is no nickel catalyst and during the reaction the substances are heated, then as a result, hydrogen atoms are added to the benzene molecule and a compound such as cyclohexane is formed. In this case, pi-bonds are broken.
Benzene (its electronic structure and propertiesdescribed in the article) is a highly flammable substance. So, in the air, it quickly lights up, and a mixture of its vapors with oxygen generally explodes. In this case, benzene is resistant to oxidants, such as potassium permanganate and nitric acid. Owing to the oxidation reaction with ozone, the structure of the substance was established.
Industrial benzene, the physical properties of whichdescribed in this article, until the middle of the last century was extracted from coal tar. However, since the 50s of the 20th century a new method for obtaining industrial benzene was discovered. For this, it is necessary to carry out dehydrogenation of oil raw materials. There are following ways of production of this substance:
- Coking coal - the oldestmethod. Before the outbreak of World War II, he was considered the main source of benzene. Currently, it is used much less often, only 10 percent of the substance is obtained with its help.
- The method of catalytic reforming of gasolineoil fractions. In the US, this method is used most widely. In countries such as Russia and Japan, as well as in Western Europe, this method produces 40 to 60 percent of the substance. In this process, additional compounds are formed. Sometimes they are processed into benzene or a mixture thereof.
- Almost half of the world's benzene is minedby pyrolysis of oil fractions, as a rule, gasoline. As a result, not only the desired substance is formed, but also toluene, as well as xylene. They are turned into the necessary connection.
- If you conduct acetylene over activated carbon at a temperature of 600 degrees Celsius, then you can get several aromatic hydrocarbons, including benzene.
Benzene, the physical properties of which are indicatedabove, serves as a raw material for organic synthesis for industrial purposes. Two-thirds of the extracted matter goes to the production of compounds such as cyclohexane, cumene. Previously, benzene was used in street lamps.
A huge amount of substance is spent on obtaining nitrobenzene, which is subsequently reduced to aniline. Technically, this reaction proceeds as follows:
- There is an effect of hydrochloric acid on benzene. The presence of iron is necessary.
- It reacts to the acid, resulting in the formation of hydrogen atoms, in fact, it affects the formation of aniline.
It is used to synthesize various dyes and medicines.
Benzene is consumed to produce phenol. It produces phenol-formaldehyde resins. Such a substance as hexachlorocyclohexane has become widely used as a means for controlling insects and pests. It is widely used in agriculture.
Benzene (chemical and physical properties briefly described in this article) is part of a fuel such as gasoline. Since the substance is very toxic, its content does not exceed five percent.
Advantages and disadvantages
Benzene (the physical properties of the substance are described inthis article) is very much appreciated as a solvent. However, it has a high toxicity and carcinogenicity, so the substance has not been widely used as a solvent.
Benzene, extracted from coal tar, is not suitable for several technological processes. The fact is that it contains too much thiophene.