One of the representatives of aromatic hydrocarbons is benzene. The structure, physical properties of this substance are presented in this article.
History
The benzene compound was discovered before all arenas. Michael Faraday brought him out by distilling crystals of luminous gas. Another way is to decompose whale oil under the influence of high temperatures. Another scientist, namely Mitcherlich, in 1834 received benzene, the physical properties of which were not studied at that time, by dry distillation of the acid of the same name with the addition of lime.
The scientist proposed the name "gasoline" for this substance. However, a person researching the properties and composition of benzene gave him the usual naming convention. Translated from German, "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, since they had a pleasant smell.
Composition
There is such a thing as raw benzene. Physical properties and application directly depend on the composition of the substance. So, benzene contains a large amount of substances, for example, pyridine, coumarons, cumene, even naphthalene. To turn the crude product into pure, benzene is purified and rectified.
Cleaning is carried out as follows: the substance is washed successively in an alkali solution, in acid and in water. To remove the bases and phenols from the crude product, it is first purified with sulfuric acid.
Formula
For the first time, the resulting substance was written in the form of an incorrect formula, which looked like this: C2H2.
Michael Faraday made a mistake, because at that time the atomic mass of carbon was taken as 6 amu Another scientist, whose name was Mitcherlich, wrote down the formula correctly - C6H6.
Homologues
Like other hydrocarbons, benzene forms a homologous series. Its simplest homologue is a substance called methylbenzene. Its technical name is toluene. This is a liquid that has no color, but has a characteristic odor. The physical and chemical properties of benzene and methylbenzene are similar.
The substance is extracted with benzene, then it is separated by fractional distillation. Most often, toluene is used for the production of explosives, especially TNT.
Physical properties
The following physical properties of benzene and its homologs exist:
- Substances are in a liquid state of aggregation. Benzene boils at a temperature of 80.1 degrees Celsius. In a frozen state it turns into a crystalline mass of white. The compound hardens at a temperature of 5.5 degrees.
- Benzene is a non-polar substance that does not dissolve in water. In this case, a mixture is formed whose boiling point is 69.25 degrees. Its composition does not change during the transition from one state of aggregation to another. The compound is mixed with most non-polar solvents.
These were the basic physical properties of benzene. The table in which all information about them is indicated, of course, will be much larger.
Chemical reactions
With the participation of benzene, in most cases substitution reactions occur , however , addition or oxidation reactions also take place.
In addition reactions, the substance acts as a unsaturated hydrocarbon. If there is no nickel catalyst, and during the reaction the substances are heated, 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 properties are described in the article) is a highly flammable substance. So, in air, it quickly ignites, and the mixture of its vapor with oxygen explodes altogether. In this case, benzene is resistant to oxidizing agents such as potassium permanganate and nitric acid. Due to the oxidation reaction with ozone, the structure of the substance was established.
Getting
Industrial benzene, the physical properties of which are described in this article, was mined from coal tar until the middle of the last century. However, since the 50s of the 20th century, a new method for producing industrial benzene was discovered. For this, it is necessary to dehydrogenate the crude oil. The following production routes for this substance exist:
- Coal coking is the oldest method. Before the start of World War II, it was he who was considered the main source of benzene. Currently, it is used much less frequently, only 10 percent of the substance is obtained with its help.
- The method of catalytic reforming of gasoline fractions of oil. In the United States, this method is most widely used. In such countries as Russia and Japan, as well as in Western Europe, 40–60 percent of the substance is obtained using this method. In this process, the formation of additional compounds. Sometimes they are processed into benzene or its mixture.
- Almost half of world benzene is extracted by pyrolysis of petroleum fractions, usually gasoline. As a result, not only the desired substance is formed, but also toluene, as well as xylene. They are turned into the necessary compound.
- If you hold acetylene over activated carbon at a temperature of 600 degrees Celsius, you can get several aromatic hydrocarbons, including benzene.
Application
Benzene, the physical properties of which are indicated above, serves as a raw material for organic synthesis for industrial purposes. Two-thirds of the extracted material goes to the production of compounds such as cyclohexane, cumene. Previously, benzene was used in street lamps.
A huge amount of the substance is spent on the production of nitrobenzene, which is subsequently reduced to aniline. Technically, this reaction proceeds as follows:
- The effect of hydrochloric acid on benzene. The presence of iron is required.
- It reacts to acid, resulting in the formation of hydrogen atoms, in fact, it affects the formation of aniline.
It is used to synthesize both various dyes and medicines.
Benzene is consumed to produce phenol. Phenol-formaldehyde resins are made from it. A substance such as hexachlorocyclohexane is widely used as a means of combating insects and pests. It is widely used in agriculture.
Benzene (the chemical and physical properties are 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 described in this article) is very much appreciated as a solvent. However, it has high toxicity and carcinogenicity, so the substance is not widely used as a solvent.
Benzene extracted from coal tar is unsuitable for several technological processes. The fact is that it contains too much thiophene.