Nitrobenzene (C6H5NO2) structure, properties, uses, risks

The nitrobenzene is an aromatic organic compound formed by a benzene ring C₆H₅- and a nitro -NO group_two. Its chemical formula is C₆H₅NOT_two. It is a colorless or pale yellow oily liquid, smelling of bitter almonds or shoe polish.

Nitrobenzene is a very useful compound in the chemical industry because it makes it possible to obtain a series of chemical substances that have various uses. This is because it can be subjected to various types of reactions.

Important chemical reactions include nitration (which allows more -NO groups to be added_two to the molecule) and reduction (the opposite of oxidation since the two oxygen atoms of the nitro -NO group are eliminated_two and are replaced by hydrogens).

With nitrobenzene, for example, aniline and para-acetaminophenol can be prepared. The latter is the well-known acetaminophen which is an antipyretic (medicine against fever) and mild analgesic (medicine against minor pain)..

Nitrobenzene should be handled with caution as it is irritating and toxic, it can cause a type of anemia, among several symptoms, and it is believed to cause cancer. It is also harmful to the environment.

Article index

• 1 Structure
• 2 Nomenclature
• 3 Properties
  • 3.1 Physical state
  • 3.2 Molecular weight
  • 3.3 Melting point
  • 3.4 Boiling point
  • 3.5 Flash point
  • 3.6 Autoignition temperature
  • 3.7 Density
  • 3.8 Solubility
  • 3.9 Chemical properties
  • 3.10 Dimer formation
  • 3.11 Other properties
• 4 Obtaining
• 5 Uses
  • 5.1 In obtaining aniline and acetaminophen
  • 5.2 In obtaining other chemical compounds
  • 5.3 In various applications
• 6 Risks
• 7 Treatments for its elimination from the environment
• 8 References

Structure

Nitrobenzene C₆H₅-NOT_two is a flat molecule formed by a benzene ring C₆H₅- to which a nitro -NO group is attached_two. Its molecule is flat because there is an electronic interaction between the nitro -NO group_two and the benzene ring.

The nitro -NO group_two tends to attract electrons from the benzene ring C₆H₅-.

Therefore, the molecule has a slightly more negative side (where the oxygens of -NO_two) and a slightly more positive side (the benzene ring).

Nomenclature

- Nitrobenzene.

- Nitrobenzine.

- Nitrobenzole.

- Myrban or myrban oil or essence (disused term).

Properties

Physical state

Colorless to pale yellow oily liquid.

Molecular weight

123.11 g / mol.

Melting point

5.7 ºC.

Boiling point

211 ºC.

Flashpoint

88 ºC (closed cup method).

Autoignition temperature

480 ° C.

Density

1.2037 g / cm³ at 20 ºC.

Solubility

Slightly soluble in water: 0.19 g / 100 g of water at 20 ° C. Fully miscible with alcohol, benzene and diethyl ether.

Chemical properties

Nitrobenzene is stable up to approximately 450 ° C temperature at which it begins to decompose forming (in the absence of oxygen) NO, NO_two, benzene, biphenyl, aniline, dibenzofuran, and naphthalene.

Important nitrobenzene reactions include reduction, nitration, halogenation, and sulfonation..

Nitration of nitrobenzene initially produces metha-nitrobenzene and with a prolonged reaction time 1,3,5-nitrobenzene is obtained.

Reacting bromine or chlorine with nitrobenzene in the presence of an appropriate catalyst gives 3-bromo-nitrobenzene (meta-bromonitrobenzene) or 3-chloro-nitrobenzene (meta-chloronitrobenzene).

An example of reduction is that when treating with tin (Sn) in hydrochloric acid (HCl) the meta-halogenonitrobenzenes are obtained meta-halogenoanilinas.

Nitrobenzene sulfonation is carried out with fuming sulfuric acid at 70-80 ° C and the product is meta-nitrobenzenesulfonic acid. This can be reduced with iron and HCl to give methanilic acid..

Dimer formation

In a solution of benzene C₆H₆ nitrobenzene molecules associate with each other to form dimers or pairs of molecules. In these pairs, one of the molecules is in an inverted position with respect to the other..

The formation of nitrobenzene dimers with molecules one in an inverted position with respect to the other is possibly due to each of them having a slightly more positively charged side and an opposite side with a slightly more negative charge..

In the dimer, the side with a slightly more positive charge of one of the molecules is possibly located close to the slightly negative charge of the other molecule, since the opposite charges attract each other, and this is the case with the other two sides..

Other properties

Has an odor similar to almonds or shoe polish. When lowering its temperature it solidifies in the form of greenish yellow crystals.

Obtaining

Obtained by treating benzene C₆H₆ with a mixture of nitric acid HNO₃ and sulfuric acid H_twoSW₄. The process is called nitration and involves the formation of the nitronium ion NO_two⁺ thanks to the presence of sulfuric acid H_twoSW₄.

- Nitronium ion NO formation_two⁺:

HNO₃ + 2 h_twoSW₄ ⇔ H₃OR⁺ + 2 HSO₄^- + NOT_two⁺ (nitronium ion)

- Nitronium ion attacks benzene:

C₆H₆ + NOT_two⁺ → C₆H₆NOT_two⁺

- Nitrobenzene is formed:

C₆H₆NOT_two⁺ + HSO₄^- → C₆H₅NOT_two + H_twoSW₄

In summary:

C₆H₆ + HNO₃ → C₆H₅NOT_two + H_twoOR

The nitration reaction of benzene is very exothermic, that is, a lot of heat is generated, so it is very dangerous.

Applications

In obtaining aniline and acetaminophen

Nitrobenzene is mainly used to synthesize aniline C₆H₅NH_two, which is a compound widely used for the preparation of pesticides, gums, dyes, explosives and medicines.

Obtaining aniline occurs by reducing nitrobenzene in an acid medium in the presence of iron or tin, which is carried out according to the following steps:

Nitrobenzene → Nitrosobenzene → Phenylhydroxylamine → Aniline

C₆H₅NOT_two → C₆H₅NO → C₆H₅NHOH → C₆H₅NH_two

Depending on the conditions, the process can be stopped in one of the intermediate steps for example phenylhydroxylamine. Starting from phenylhydroxylamine in a strongly acidic medium, para-aminophenol can be prepared:

Phenylhydroxylamine → p-Aminophenol

C₆H₅NHOH → HOC₆H₄NH_two

The latter is treated with acetic anhydride to obtain paracetamol (acetaminophen), a known antipyretic and mild analgesic, that is, a medicine to treat fever and pain..

Another way to obtain aniline is by reducing nitrobenzene with carbon monoxide (CO) in an aqueous medium in the presence of very small particles (nanoparticles) of palladium (Pd) as a catalyst..

C₆H₅-NOT_two + 3 CO + H_twoO → C₆H₅-NH_two + 3 CO_two

In obtaining other chemical compounds

Nitrobenzene is the starting point to obtain a great variety of compounds used as colorants, pesticides, medicines and cosmetics.

For example, it makes it possible to obtain 1,3-dinitrobenzene, which by chlorination (addition of chlorine) and reduction (elimination of oxygen atoms) generates 3-chloroaniline. This is used as an intermediate for pesticides, dyes and medicines.

Nitrobenzene was used to prepare benzidine which is a dye. In addition, nitrobenzene is used to prepare quinoline, azobenzene, methanilic acid, dinitrobenzene, isocyanates or pyroxylin among many other compounds..

In various applications

Nitrobenzene is used or has been used as:

- Extraction solvent for the purification of lubricating oils used in machinery

- Solvent for cellulose ethers

- Metal polishing mix ingredient

- In soaps

- In shoe polishing mixtures

- Spray paint preservative

- Component of floor polishing mixes

- Almond essence substitute

- In the perfume industry

- In the production of synthetic rubber

- Solvent in various processes

Risks

Nitrobenzene is toxic by inhalation, ingestion, and absorption through the skin..

Irritating to skin, eyes and respiratory tract. It can cause a type of anemia called methemoglobinemia, which is a reduction in the ability of red blood cells to release oxygen into the tissues and leads to fatigue..

In addition, nitrobenzene causes dyspnea, dizziness, impaired vision, shortness of breath, collapse, and death. It also damages the liver, spleen, kidneys and central nervous system.

It is estimated that it can be a mutagen and possibly a cause of cancer in humans, since it has caused it in animals.

Additionally nitrobenzene should not be disposed of in the environment. Its toxicity towards animals, plants and microorganisms makes it very harmful to ecosystems.

Toxicity towards microorganisms reduces their biodegradability.

Treatments for its elimination from the environment

Contamination of the environment with nitrobenzene can occur through waste from the various industries that use it, such as the dye or explosives industry..

Nitrobenzene is a highly toxic pollutant and difficult to decompose under natural conditions, for this reason it can cause severe contamination of drinking water and crop irrigation systems..

Due to its high stability and toxicity towards microorganisms, it is often selected as a model in sewage treatment studies..

Various ways to remove nitrobenzene from contaminated water are being investigated. One of them is through photocatalytic degradation, that is, using sunlight as an accelerator of the degradation reaction in the presence of titanium dioxide TiO_two.

Microelectrolysis methods with an iron (Fe) and copper (Cu) catalyst in ceramic have also been successfully tested. Microelectrolysis allows nitrobenzene to be broken down by an electrical current.

References

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2. Morrison, R.T. and Boyd, R.N. (2002). Organic Chemistry. 6th Edition. Prentice-Hall.
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4. Smith, P.W.G. et al. (1969). Aromatic nitration-Nitro compounds. Electrophilic Substitutions. In Aromatic Chemistry. Recovered from sciencedirect.com.
5. Windholz, M. et al. (editors) (1983). The Merck Index. An Encyclopedia of Chemicals, Drugs, and Biologicals. Tenth Edition. Merck & CO., Inc.
6. Ullmann's Encyclopedia of Industrial Chemistry. (1990). Fifth Edition. Volume A22. VCH Verlagsgesellschaft mbH.
7. Whang, T.-J. et al. (2012). UV-Irradiated Photocatalytic Degradation of Nitrobenzene by Titania Binding on Quartz Tube. International Journal of Photoenergy, Volume 2012, Article ID 681941. Recovered from hindawi.com.
8. Shikata, T. et al. (2014). Nitrobenzene anti-parallel dimer formation in non-polar solvents. AIP Advances 4, 067130 (2014). Recovered from doaj.org.
9. Krogul-Sobczak, A. et al. (2019). Reduction of Nitrobenzene to Aniline by CO / H_twoO in the Presence of Palladium Nanoparticles. Catalysts 2019, 9, 404. Recovered from mdpi.com.
10. Yang, B. et al. (2019). Pilot-Scale Production, Properties and Application of Fe / Cu Catalytic-Ceramic-Filler for Nitrobenzene Compounds Wastewater Treatment. Catalysts 2019, 9, 11. Recovered from mdpi.com.