Nitrobenzene Formula: Physical and Chemical Properties - ONEKU

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What is nitrobenzene? This is an organic compound, which is an aromatic nucleus and an attached nitro group. In appearance, depending on temperature, it is bright yellow crystals or an oil liquid. Has almond smell. Toxic.

What is nitrobenzene? This is an organic compound, which is an aromatic nucleus and an attached nitro group. In appearance, depending on temperature, it is bright yellow crystals or an oil liquid. Has almond smell. Toxic.

Structural formula Nitrobenzene.

Nitro group is a very strong electronic density acceptor. Therefore, the nitrobenzene molecule has a negative inductive and negative mesomeric effect. The nitro group quite strongly attracts the electronic density of the aromatic kernel, deactivating it. The electrophilic reagents are no longer treated so much to the kernel, and therefore nitrobenzene does not actively enter such reactions. In order to directly attach another nitro group to Nitrobenzene, very hard conditions are needed, much more rigid than with mononitrobenzene synthesis. The same applies to halogen, sulfogroups, etc.

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From the structural formula of nitrobenzene it can be seen that one nitrogen connection with oxygen is single, and the other is double. But in fact, due to the mesomeric effect, they both are equivalent and have the same length of 0.123 nm.

Obtaining nitrobenzene in industry

Nitrobenzene is an important intermediate product in the synthesis of many substances. Therefore, it is produced on an industrial scale. The main method of obtaining nitrobenzene is the nitration of benzene. Usually for this use a nitraulic mixture (a mixture of concentrated sulfur and nitric acid). The reaction lead 45 minutes at a temperature of about 50 ° C. The yield of nitrobenzene is 98%. That is why this method is mainly used in industry. To implement it, there are special installations both periodic and continuous type. In 1995, the production of nitrobenzene in the United States was 748,000 tons per year.

The benzene thread can also be carried out simply concentrated nitric acid, but in this case the product output will be lower.

Obtaining nitrobenzene in the laboratory

There is another way to produce nitrobenzene. Aniline (aminobenzene) is used as raw materials, which is oxidized by peroxy compounds. Due to this, the amino group is replaced by a nitro group. But during this reaction, several by-products are formed, which prevents effectively using this method in industry. Moreover, nitrobenzene is mainly used for the synthesis of aniline, so it does not make sense to use aniline for the production of nitrobenzene.

Physical properties

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At room temperature, nitrobenzene is a colorless oily liquid with a smell of bitter almond. At a temperature of 5.8 ° C, it solidifies, turning into yellow crystals. At 211 ° C, nitrobenzene boils, and at 482 ° C is self-propagated. This substance, almost like any aromatic compound, is insoluble in water, but is well soluble in organic compounds, especially in benzene. It can also distinguish with water vapor.

Electrophile replacement

For nitrobenzene, as well as for any arena, the reaction of electrical substitution in the core is characteristic, although they are somewhat difficult compared to benzene due to the influence of the nitro group. Thus, it is possible to obtain dinitrobenzene from nitrobenzene by further nitration with a mixture of nitric and gray acids at elevated temperature. The resulting product will be predominantly (93%) consist of meta-dinitrobenzene. It is possible even to obtain trinitobenzene directly. But for this it is necessary to use even more stringent conditions, as well as a three-meter boron.

Similarly, nitrobenzene can be sulphide. To do this, use a very strong sulfting reagent - oleum (sulfur oxide solution Vi in sulfuric acid). The temperature of the reaction mixture should be at least 80 ° C. Another reaction of electrophilic substitution is direct halogenation. Lewis strong acids are used as catalysts (aluminum chloride, trifluoride, etc.), as well as increased temperature.

Nucleophilic substitution

As can be seen from the structural formula, nitrobenzene can enter into reactions with strong electron donor compounds. This is possible due to the influence of the nitro group. An example of such a reaction can be the interaction with concentrated or solid hydroxides of alkali metals. But in this reaction nitrobenzene sodium is not formed. The chemical formula of nitrobenzene involves the addition of the hydroxyl group in the nucleus, i.e. the formation of nitrophenol. But this happens only at a sufficient hard environment.

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A similar reaction proceeds with magniaorganic compounds. The hydrocarbon radical joins the kernel into an ortho or paragon to the nitro group. The by-process in this case is the restoration of the nitro group to the amino group. The reactions of nucleophilic substitution are easier if nitro groups are somewhat, since they will still be pulled by the electronic density of the kernel.

Recovery reaction

As you know, nitro compounds can be recovered to amines. It is not an exception and nitrobenzene, the formula of which involves the possibility of this reaction. It is often used in industry for aniline synthesis.

But Nitrobenzene can give a lot of other recovery products. Most often, the restoration of atomic hydrogen is used at the time of its release, i.e., the reaction mixture is carried out in the reaction mixture, and the hydrogen released reacts with nitrobenzene. Usually, with this interaction, aniline is obtained.

If nitrobenzene act on the zinc dust in the ammonium chloride solution, then the reaction will be N-phenylhydroxylamine. This compound can be fairly easily restored with a standard way to aniline, or oxidized in nitrobenzene in a strong oxidizing agent.

Recovery can also be carried out in the gas phase by molecular hydrogen in the presence of platinum, palladium or nickel. In this case, aniline is also obtained, but there is a possibility of restoring the benzene nucleus itself, which is often undesirable. Sometimes such a catalyst is also used as Nickel Renae. It is a porous nickel saturated with hydrogen and containing 15% aluminum.

When the nitrobenzene is restored, potassium or sodium alcoholates are formed azoxibenzene. If you use stronger reducing agents in an alkaline environment, the azobenzene is obtained. This reaction is also quite important, as some dyes are synthesized with it. Azobenzene may be subjected to further restoration in an alkaline medium to the formation of hydrachinzene.

Initially, the reduction of nitrobenzene was carried out by ammonium sulfide. This method in 1842 suggested Zinin N. N., so the reaction carries his name. But at the moment it is rarely applied in practice due to low yield.

Application

Nitrobenzene itself is used very rarely, only as a selective solvent (for example, for cellulose ethers) or a soft oxidizer. Sometimes it is added to polishing solutions for metals.

Almost all produced nitrobenzene is used to synthesize other beneficial substances (for example, aniline), which, in turn, are used to synthesize drugs, dyes, polymers, explosives, etc.

Danger

Because of its physical and chemical properties, Nitrobenzene is a very dangerous compound. It has a third level of health hazard from four according to the NFPA 704 standard. In addition to the fact that it can get into the body when breathing or through the mucous membranes, it is also absorbed through the skin. In poisoning a large concentration of nitrobenzene, a person may lose consciousness and die. At low concentrations, the symptoms of poisoning are malaise, dizziness, noise in the ears, nausea and vomiting. Nitrobenzene poisoning feature - high infection rate. Symptoms are manifested very quickly: the reflexes are broken, the blood acquires a dark brown color due to the formation of methemoglobin. Sometimes there may be rashed on the skin. A concentration sufficient for departure is very small, although there are no accurate data on the deadly dose. In special literature, information is often found that 1-2 drops of nitrobenzene grabs to kill a person.

Treatment

In the nitrobenzene poisoning of the victim, it is necessary to immediately remove from the toxic zone and save it from infected clothes. The body is washed with warm water with soap to remove nitrobenzene from the skin. Every 15 minutes the victim make inhalation of carbogen. With light poisoning, cystamine, pyridoxine or lipoic acid is necessary. In more severe cases, it is recommended to use methylene blue or chromosmon intravenously. When nitrosnol poisoning through the mouth, it is necessary to immediately cause vomiting and rinse the stomach with warm water. Contraindicated to make any fat, including milk.

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