Ms. Chemistry in her household finally and irrevocably acquired such a compound as benzene only in 1833. Benzene is a compound that has a short-tempered, one might even say explosive character. How did you find out?
History
Johann Glauber in 1649 turned his attention to the compound, which was successfully formed when the chemist was engaged in the processing of coal tar. But it wished to remain incognito.
After about 170 years, and to be much more precise, in the mid-twenties of the XIX century, by chance, benzene was extracted from the gas of the gas, namely from the condensate released. Humanity owes such efforts to Michael Faraday, a scientist from England.
The baton for the acquisition of benzene was intercepted by the German Eilgard Mikerlich. This happened when the process of treating anhydrous calcium salts of benzoic acid took place. Perhaps that is why the compound was given the name benzene. Still, as an option, the scientist called it gasoline. Incense, if translated from Arabic.
Benzene burns beautifully and brightly, in connection with these observations, Auguste Laurent advised calling it “hair dryer” or “benzene”. Bright, brilliant - if translated from Greek.
Based on the opinion of Linus Pauling, the concept of the nature of electronic communication, 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 electron cloud, which safely encloses six (without exception) carbon atoms of the cycle. Bonded binary bonds are not observed.
They used to work with benzene as a solvent. But basically, as they say, did not consist, did not participate, was not involved. But this is in the 19th century. In XX there were significant changes. The properties of benzene express the most valuable qualities that helped him become more popular. The octane number, which turned out to be high, made it possible to use it as a fuel element for refueling cars. This action served as the impetus for the extensive seizure of benzene, the extraction of which is carried out as a secondary product of coking steelmaking.
By the forties in the chemical field, benzene began to be consumed in the manufacture of substances that explode quickly. The 20th century crowned itself with the fact that the oil refining industry produced so much benzene that it began to supply the chemical industry.
Benzene Characterization
Unsaturated hydrocarbons are very similar to benzene. For example, the hydrocarbon series of ethylene characterizes itself as an unsaturated hydrocarbon. He is characterized by a reaction of accession. Benzene willingly enters a substitution reaction. All this is due to atoms that are in the same plane. And as a fact - a conjugated electron cloud.
If a benzene ring is present in the formula, it means that we can come to the elementary conclusion that this is benzene, the structural formula of which looks just like that.
Physical properties
Benzene is a liquid that has no color, but has a regrettable smell. Benzene melts when the temperature reaches 5.52 degrees Celsius. Boils at 80.1. The density is 0.879 g / cm 3 , the molar mass is 78.11 g / mol. When burning very smokes. Forms explosive compounds when air enters. Organic thinners (gasoline, ether and others) with the described substance are combined without problems. An azeotropic compound creates with water. Heating before vaporization begins at 69.25 degrees (91% benzene). At 25 degrees Celsius it can dissolve in water 1.79 g / l.
Chemical properties
Benzene reacts with sulfuric and nitric acid. And also with alkenes, halogens, chloralanes. The substitution reaction is what is characteristic of him. The pressure temperature affects the breakthrough of the benzene ring, which takes place under rather harsh conditions.
Each benzene reaction equation can be considered in more detail.
1. Electrophilic substitution. Bromine, in the presence of a catalyst, interacts with chlorine. As a result, we get chlorobenzene:
C6H6 + 3Cl2 → C6H5Cl + HCl
2. Friedel-Crafts reaction, or benzene alkylation. The appearance of alkylbenzenes occurs due to the combination with alkanes, which are halogenated:
C6H6 + C2H5Br → C6H5C2H5 + HBr
3. Electrophilic substitution. Here is the 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 exhibits a character typical of saturated hydrocarbons. The P-electron cloud, which is in the structure of the substance in question, explains these reactions.
Various types of benzene depend on special technologies. From here comes the labeling of petroleum benzene. For example, purified and higher purification, for synthesis. I would like to separately note the homologues of benzene, and more specifically, their chemical properties. These are alkylbenzenes.
Benzene homologues are much more willing to respond. But the aforementioned reactions of benzene, namely, homologs, proceed with some difference.
Halogenation of alkylbenzenes
The form of the equation is as follows:
C6H5-CH3 + Br = C6H5-CH2Br + HBr.
The aspiration of bromine in the benzene ring is not observed. He goes to the side chain. But thanks to the Al (+3) salt catalyst, bromine boldly goes into the ring.
Alkylbenzenes nitration
Thanks to sulfuric and nitric acids, benzenes and alkylbenzenes are nitrated. Reactive alkylbenzenes. Two products are obtained from the three presented - these are para- and ortho-isomers. You can write 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 below:
C6H5CH3 + [O] → C6H5COOH.
Alkylbenzene and benzene, their hydrogenation
In the presence of an amplifier, hydrogen begins to react with benzene, as a result of which cyclohexane is formed, as described above. Similarly, alkylbenzenes are converted to alkylcyclohexanes without problems. To obtain alkylcyclohexane, it is necessary to hydrogenate the desired alkylbenzene. Basically, this is a necessary procedure for the production of a pure product. And these are far from all reactions of benzene and alkylbenzene.
Benzene production. Industry
The foundation of this production is based on the processing of components: toluene, naphtha, tar, which is released during the cracking of coal, and others. Therefore, benzene is produced at petrochemical and metallurgical enterprises. It is important to know how to obtain benzene of various degrees of purification, because the direct dependence of the brand of a given substance follows from the principle of manufacture and purpose.
The lion's share is made by thermocatalytic reforming of the caustobiolite part, boiling off at 65 degrees, having the effect of an extract, distillation with dimethylformamide.
In the production of ethylene and propylene, liquid products are obtained that are formed during the decomposition of inorganic and organic compounds under the influence of heat. Of these, benzene is isolated. But, unfortunately, there is not so much source material for this option for benzene production. Therefore, the substance of interest to us is obtained by reforming. By this method, the volume of benzene is increased.
By dealkylation at a temperature of 610-830 degrees with a plus sign, in the presence of steam formed during the boiling of water and hydrogen, benzene is obtained from toluene. There is another option - catalytic. When the presence of zeolites, or, as an option, oxide catalysts is observed, subject to a temperature regime of 227-627 degrees.
There is another, older, way to develop benzene. By absorption by absorbers of organic origin, it is isolated from the final result of coking coal. The product is steam-gas and has previously been cooled. For example, oil is used that is based on oil or coal. When the distillation is carried out with water vapor, the absorber is separated. Hydrotreating helps to free crude benzene from excess substances.
Coal raw materials
In metallurgy, when using coal, and if you specify - its dry distillation, get coke. During this procedure, air intake is limited. Do not forget that coal is heated to a temperature of 1200-1500 Celsius.
Coal chemical benzene needs thorough purification. It is necessary to get rid of methyl cyclohexane and its comrade n-heptane without fail. Saturated hydrocarbons must also be recovered. Benzene has a process of separation, purification, which will be carried out more than once.
The method described above is the oldest, but after the lapse of time it loses its high position.
Oil fractions
0.3-1.2% - these are the indicators of the composition of our hero in crude oil. Miserable indicators to invest finances and forces. It is best to use the industrial process for the processing of petroleum fractions. That is, catalytic reforming. In the presence of an aluminum-platinum-rhenium amplifier, the percentage of accommodation of aromatic carbohydrates increases, and the indicator that determines the ability of the fuel to not ignite when it is compressed increases.
Pyrolysis Resins
If our oil product is extracted from non-solid raw materials, namely, by pyrolysis of propylene and ethylene during the manufacture, this approach will turn out to be the most acceptable. To be precise, benzene is released from the pyrocondensate. The decomposition of certain fractions requires hydrotreating. When cleaning, sulfur and unsaturated mixtures are removed. In the initial result, the content of xylene, toluene, benzene was noted. Using the haul, which is extractive, the BTK group is separated and benzene is obtained.
Toluene hydrodealkylation
The protagonists of the process, a cocktail of hydrogen stream and toluene, are served heated in the reactor. 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).
Toluene Disproportionation
As a result of methyl class rejection, creation to benzene takes place, xylene is oxidized. In this process, transalkylation was observed. The action of catalysis occurs due to palladium, platinum and neodymium, which are on alumina.
Taluene and hydrogen are fed into a reactor with a stable catalyst bed. Its purpose is to keep the subsidence of the hydrocarbon catalyst on the plane. The stream that leaves the reactor is cooled, and hydrogen is safely recovered for recycling. What is left is distilled three times. At the initial stage, compounds that are non-aromatic are withdrawn. Benzene is produced in the second, and the last step is the isolation of xylenes.
Acetylene Trimerization
Thanks to the work of the French physicist-chemist Marceline Berthelot, benzene was produced from acetylene. But at the same time a heavy cocktail stood out from many other elements. 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 turned out to be nickel. Trimerization is the only option to get benzene from acetylene.
The formation of benzene occurs using activated carbon. At high heat values, acetylene passes over coal. Benzene is released if the temperature is at least 410 degrees. In this case, a variety of aromatic hydrocarbons are still born. Therefore, good equipment is needed that is capable of high-quality purification of acetylene. With such a time-consuming method, as trimerization, acetylene is consumed a lot. To get 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 (Zelinsky equation).
3CH → CH = (t, kat) = C6H6.
Where is benzene used?
Benzene is a fairly popular brainchild of chemistry. Especially often it was noticed how benzene was adopted in the manufacture of cumene, cyclohexane, ethylbenzene. To create styrene, ethylbenzene is indispensable. The starting material in order to develop caprolactam is cyclohexane. When making a thermoplastic resin, it is caprolactam that is used. The described 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 malaise, which is accompanied by nausea and severe dizziness, is a sign of poisoning. Even death is not ruled out. A feeling of indescribable delight is no less disturbing bells in benzene poisoning.
Liquid benzene causes skin irritation. Benzene vapors easily penetrate even through intact skin. With the most short-term contacts with the substance in a small dose, but on a regular basis, unpleasant consequences will not take long. This can be a lesion of bone marrow and acute leukemia of a different nature.
In addition, the substance causes dependence in humans. Benzene acts like a dope. A tar-like product is obtained from tobacco smoke. After studying it, we came to the conclusion that the content of the latter is unsafe for humans. In addition to the presence of nicotine, the presence of aromatic carbohydrates of the type of benzpyrene was also found. A distinctive feature of benzpyrene are carcinogens. They have a very harmful effect. For example, cause cancer.
Despite the above, benzene is the starting material for the production of a variety of pharmaceuticals, plastics, synthetic rubber and, of course, dyes. This is the most common brainchild of chemistry and aromatic compound.