Benzene is ... Structural formula, properties and production of benzene

By such a compound as benzene, Mrs. Chemistry in its economy finally and irrevocably acquired only in 1833. Benzene is a compound that has an irascible, you might say even explosive character. How did you find this out?

History

In 1649, Johannes Glauber turned his attention to a compound that was safely formed when the chemist was working on the processing of coal tar. But it wanted to remain incognito.

After about 170 years, and to be much more precise, in the mid-twenties of the XIX century, by the will of the case, benzene was extracted from the light gas, namely from the condensate that was released. To such diligence humanity is obliged to Michael Faraday, a scientist from England.

The baton for the acquisition of benzene was intercepted by the German Eilgard Micherlich. This happened when processing the anhydrous calcium salts of benzoic acid. Perhaps this is why the name was given the name "benzene". Still, as an option, the scientist called him gasoline. Incense, if translated from Arabic.

Benzene beautifully and brightly burns, in connection with these observations, Auguste Laurent advised him to call him "hair dryer" or "benzene". Bright, glistening - if translated from Greek.

Based on the opinion of Linus Pauling, the concept of the nature of electronic communication, about the qualities of benzene, the scientist provided the molecule of the compound in the form of the following image. This is a hexagon. A circle is inscribed in it. The foregoing indicates that benzene has an integral electronic cloud that safely encloses six (without exception) carbons of the cycle. Bonded bonds are not observed.

With benzene used to work as a solvent. And basically, as they say, was not, did not participate, was not involved. But this is in the XIX century. In XX there were significant changes. The properties of benzene express the most valuable qualities that have helped it become more popular. The octane number, which turned out to be high, provided an opportunity to use it as an element of fuel for fueling cars. This action was the impetus for the extensive seizure of benzene, the extraction of this is carried out as a secondary product of coking of steelmaking.

By the 1940s in the chemical sphere, benzene began to be consumed in the manufacture of substances that quickly exploded. The twentieth century crowned itself with the fact that the oil refining industry developed benzene so much that it began supplying the chemical industry.

Characteristics of benzene

Unsaturated hydrocarbons are very similar to benzene. For example, the hydrocarbon series of ethylene characterizes itself as an unsaturated hydrocarbon. He is characterized by the reaction of accession. Benzene readily enters a substitution reaction. All this is due to atoms that are in the same plane. And as fact - a conjugate electronic cloud.

If there is a benzene ring in the formula, then you can come to the elementary conclusion that it is benzene, the structural formula of which looks exactly like this.

Physical properties

Benzene is a liquid that has no color, but has a regrettable odor. The benzene melts when the temperature reaches 5.52 degrees Celsius. It boils at 80.1. The density is 0.879 g / cm ³ , the molar mass is 78.11 g / mol. He burns strongly during combustion. Forms explosive compounds when air enters. Thinners of organic rock (gasoline, ether and others) with the described substance are connected without problems. Azeotropic compound creates with water. Heating to the beginning of vaporization occurs at 69.25 degrees (91% benzene). At 25 degrees Celsius, it can dissolve in water at 1.79 g / l.

Chemical properties

Benzene reacts with sulfuric and nitric acid. And also with alkenes, halogens, chloroalkanes. The reaction of substitution is what is peculiar to him. The pressure temperature affects the breakthrough of the benzene ring, which takes place under rather harsh conditions.

Each equation of the benzene reaction can be considered in more detail.

1. Electrophilic substitution. Bromine, in the presence of a catalyst, reacts with chlorine. As a result, we obtain chlorobenzene:

C6H6 + 3Cl2 → C6H5Cl + HCl

2. Friedel-Crafts reaction, or alkylation of benzene. The appearance of alkylbenzenes is due to the combination with alkanes, which are halogenated derivatives:

C6H6 + C2H5Br → C6H5C2H5 + HBr

3. Electrophilic substitution. Here there is a reaction of nitration and sulfonation. The benzene equation will look like this:

C6H6 + H2SO4 → C6H5SO3H + H2O

C6H6 + HNO3 → C6H5NO2 + H2O

4. Benzene during combustion:

2C6H6 + 15O2 → 12CO2 + 6H2O

Under certain conditions, it manifests a character characteristic of saturated hydrocarbons. The P-electron cloud, which is in the structure of the substance under consideration, explains these reactions.

Different types of benzene depend on special technology. Hence the marking of petroleum benzene. For example, purified and higher purification, for synthesis. I would like to separately note homologues of benzene, and more specifically, their chemical properties. These are alkylbenzenes.

Homologues of benzene react much more readily. But the aforementioned reactions of benzene, namely homologues, pass with some difference.

Halogenation of alkylbenzenes

The form of the equation is:

C6H5-CH3 + Br = C6H5-CH2Br + HBr.

The desire for bromine in the benzene ring is not observed. It comes out in a chain from the side. But thanks to the catalyst of the salt Al (+3) bromine boldly goes into the ring.

Nitration of alkylbenzenes

Due to sulfuric and nitric acids, benzenes and alkylbenzenes are nitrated. Reactive alkyl benzenes. Two products are obtained from the presented three - these are para- and ortho-isomers. One can write down one of the formulas:

C6H5-CH3 + 3HNO3 → C6H2CH3 (NO2) 3.

Oxidation

For benzene, this is unacceptable. But alkylbenzenes react willingly. For example, benzoic acid. The formula is given below:

C6H5CH3 + [O] → C6H5COOH.

Alkylbenzene and benzene, their hydrogenation

In the presence of an amplifier, hydrogen begins to react with benzene, resulting in the formation of cyclohexane, as discussed above. Similarly, alkylbenzenes are converted to alkyl cyclohexanes without problems. In order to obtain alkylcyclohexane, the desired alkyl benzene must be hydrogenated. Basically, this is a necessary procedure for the production of a pure product. And this is not all the reactions of benzene and alkylbenzene.

Production of benzene. Industry

The foundation of such production is based on the processing of constituents: toluene, naphtha, tar, which is released during the cracking of coal, and others. Therefore, benzene is produced in petrochemical, metallurgical enterprises. It is important to know how to obtain benzene of different degree of purification, because the principle of production and destination should be a direct dependence of the brand of this substance.

The lion's share is made by thermocatalytic reforming of the caustobiolithic part boiling out at 65 degrees, having the effect of extract, distillation with dimethylformamide.

In the production of ethylene and propylene, liquid products are produced that are formed during the decomposition of inorganic and organic compounds under the influence of heat. Of these, benzene is also released. But, unfortunately, there is not a lot of source material for this variant of benzene production. Because the substance of interest to us is extracted by reforming. By this method, the benzene volume is increased.

By dealkylation at a temperature of 610-830 degrees with a plus sign, in the presence of steam produced by boiling water and hydrogen, benzene is obtained from toluene. There is another option - catalytic. When there is a presence of zeolites, or alternatively, oxide catalysts, if the temperature regime is observed to be 227-627 degrees.

There is one more, older way of developing benzene. With the help of absorption by absorbers of organic origin, it is isolated from the final result of coking coal. The product is vapor-gas and pre-cooled. For example, in the process oil is launched, the source of which is oil or coal. When the distillation is carried out with water vapor, the absorber separates. Hydrotreating helps to remove raw benzene from excess substances.

Coal materials

In metallurgy using coal, and if you specify - its dry distillation, get coke. During this procedure, the intake of air is limited. Do not forget that the temperature of 1200-1500 Celsius heated coal.

Carbon-based benzene requires thorough cleaning. It is necessary to get rid of the methyl cyclohexane and its n-heptane companion. Saturated hydrocarbons should also be withdrawn. Benzol will have a process of separation, purification, which will be carried out more than once.

The method described above is the oldest, but after time it loses its high positions.

Oil fractions

0,3-1,2% - such indicators of the composition of our hero in crude oil. Minor indicators to invest finances and strength. It is best to involve an industrial procedure for processing petroleum fractions. That is catalytic reforming. In the presence of an alumino-platinum-rhenium amplifier, the percentage of aromatic carbohydrates is increasing, and the index that determines the fuel's capabilities does not spontaneously ignite when it is compressed.

Pyrolysis resins

If we extract our petroleum from not solid raw materials, namely by pyrolysis of propylene and ethylene arising during the manufacture, this approach will be most acceptable. To be precise, benzene is released from pyro-condensate. The decomposition of certain fractions requires hydrotreating. Sulfuric and unsaturated mixtures are removed during cleaning. In the initial result, the content of xylene, toluene, benzene was noted. With the help of the distillation, which is ecstatic, the BTK group is separated and benzene is obtained.

Hydrodealkylation of toluene

The main characters of the process, a cocktail from the hydrogen stream and toluene, are fed to the reactor heated. Toluene passes through the catalyst bed. During this process, the methyl group is separated to form benzene. A certain method of purification is appropriate here. The result is a highly pure substance (for nitration).

Disproportionation of toluene

As a consequence of the rejection of the methyl class, creation is made up to benzene, xylene is oxidized. In this process, transalkylation has been observed. The action of catalysis is due to palladium, platinum and neodymium, which are found on aluminum oxide.

The reactor with a stable formation of the catalyst is fed with toluene and hydrogen. Its purpose - to keep the subsidence on the plane of the catalyst of hydrocarbons. The stream that leaves the reactor undergoes cooling, and hydrogen is safely removed for recycling. That which remains is distilled thrice. At the initial stage, compounds that are non-aromatic are withdrawn. The second is extracted with benzene, and the last step is the isolation of xylenes.

Acetylene trimerization

Thanks to the works of the French physicist Marcelena Berthelot from acetylene began to make benzene. But at the same time a heavy cocktail from many other elements stood out. The question was how to lower the reaction temperature. The answer was received only in the late forties of the XX century. V. Reppe found the appropriate catalyst, it was nickel. Trimerization is the only option to obtain benzene from acetylene.

The formation of benzene occurs with the help of activated carbon. At high rates of heat above the coal is acetylene. Benzene is released if the temperature is at least 410 degrees. In this case, a variety of aromatic hydrocarbons are born. Therefore, good equipment is needed, which is able to clean acetylene qualitatively. With such a laborious method as trimerization, acetylene consumes a lot. To obtain 15 ml of benzene, 20 liters of acetylene are taken. You can see how it looks in the formula (acetylene-benzene), the reaction will not take long.

3C2H2 → C6H6 (the Zelinsky equation).

3CH → CH = (t, kat) = C6H6.

Where is benzene used

Benzene - this is a fairly popular child of chemistry. Especially often it was noticed how benzene was used in the manufacture of cumene, cyclohexane, ethylbenzene. To create styrene without ethylbenzene is indispensable. The starting material for the production of caprolactam is cyclohexane. Producing thermoplastic resin, it is used caprolactam. This substance is indispensable in the manufacture of various paints, varnishes.

How dangerous is benzene

Benzene is a toxic substance. The manifestation of a feeling of indisposition, which is accompanied by nausea and severe dizziness - is a sign of poisoning. Even death is not ruled out. Feeling of indescribable delight - this is no less disturbing bells when poisoning with benzene.

Benzene in the liquid state causes skin irritation. Benzene fumes easily penetrate even through intact skin. At the most short-term contacts with the substance in a small dose, but on a regular basis, unpleasant consequences will not take long to wait. This can be a defeat of the bone marrow and leukemia of an acute nature of a different kind.

In addition, the substance causes dependence in humans. Benzene acts as a dope. From tobacco smoke, a tar-like product is obtained. The code he studied, then came to the conclusion that the content of the latter is unsafe for humans. In addition to the presence of nicotine, there was also the presence of aromatic carbohydrates of the benzpyrene type. A distinctive feature of benzpyrene are carcinogens. They are very harmful. For example, cause cancer.

Despite the foregoing, benzene is the starting material for the production of a variety of drugs, plastics, synthetic rubber and, of course, dyes. This is the most common brainchild of chemistry and aromatic compound.