- Structure
- Nomenclature
- Properties
- Physical state
- Molecular weight
- Melting point
- Boiling point
- Flashpoint
- Autoignition temperature
- Density
- Solubility
- Chemical properties
- Dimer formation
- Other properties
- Obtaining
- Applications
- In obtaining aniline and acetaminophen
- In obtaining other chemical compounds
- In various applications
- Risks
- Treatments for its elimination from the environment
- References
The nitrobenzene is an aromatic organic compound consisting of a benzene ring C 6 H 5 - and a nitro group -NO 2. Its chemical formula is C 6 H 5 NO 2. 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 allows obtaining a series of chemical substances that have various uses. This is because it can be subjected to various types of reactions.
Nitrobenzene, C 6 H 5 -NO 2. Author: Marilú Stea.
Among the important chemical reactions are nitration (which allows adding more –NO 2 groups to the molecule) and reduction (the opposite of oxidation, since the two oxygen atoms of the nitro –NO 2 group are eliminated and 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 a 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.
Structure
Nitrobenzene C 6 H 5 –NO 2 is a flat molecule formed by a benzene C 6 H 5 ring - to which a nitro –NO 2 group is attached. Its molecule is flat because there is an electronic interaction between the nitro -NO 2 group and the benzene ring.
Flat structure of the nitrobenzene molecule. The electrons of the double bonds of the benzene ring tend to interact with the nitro -NO 2 group. Author: Benjah-bmm27. Source: Wikimedia Commons.
The nitro -NO 2 group tends to attract electrons from the benzene C 6 H 5 - ring.
Resonance structures of nitrobenzene. The benzene ring tends to have a positive charge, while the nitro -NO2 group tends to have a negative charge. The original uploader was Samuele Madini at Italian Wikipedia.. Source: Wikimedia Commons.
For this reason, the molecule has a slightly more negative side (where the –NO 2 oxygens are) and a slightly more positive side (the benzene ring).
Nitro group oxygens have a slightly negative charge compared to the benzene ring. Author: Marilú Stea.
Nomenclature
- Nitrobenzene.
- Nitrobenzine.
- Nitrobenzole.
- Oil or essence of myrban or myrban (term in disuse).
Properties
Physical state
Colorless to pale yellow oily liquid.
Molecular weight
123.11 g / mol.
Melting point
5.7 ° C.
Boiling point
211 ° C.
Flashpoint
88 ºC (closed cup method).
Autoignition temperature
480 ° C.
Density
1.2037 g / cm 3 at 20 ° C.
Solubility
Slightly soluble in water: 0.19 g / 100 g of water at 20 ° C. Completely miscible with alcohol, benzene and diethyl ether.
Chemical properties
Nitrobenzene is stable up to about 450 ° C where it begins to decompose forming (in the absence of oxygen) NO, NO 2, 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 long reaction time 1,3,5-nitrobenzene is obtained.
By reacting bromine or chlorine with nitrobenzene in the presence of an appropriate catalyst, 3-bromo-nitrobenzene (meta-bromonitrobenzene) or 3-chloro-nitrobenzene (meta-chloronitrobenzene) is obtained.
An example of reduction is that when treating meta-halogenonitrobenzenes with tin (Sn) in hydrochloric acid (HCl) meta-halogenoanilines are obtained.
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 C 6 H 6 benzene solution, nitrobenzene molecules associate with each other, forming 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 inverted relative to the other is possibly due to each of them having a slightly more positively charged side and an opposite slightly more negatively charged side.
In the dimer, the slightly more positively charged side of one of the molecules is possibly close to the slightly negatively charged of the other molecule, since the opposite charges attract, and so it is with the other two sides.
Nitrobenzene dimer, that is, two molecules that tend to hang together in some solvents. Author: Marilú Stea.
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
It is obtained by treating benzene C 6 H 6 with a mixture of nitric acid HNO 3 and sulfuric acid H 2 SO 4. The process is called nitration and involves the formation of the nitronium ion NO 2 + thanks to the presence of sulfuric acid H 2 SO 4.
- Formation of the nitronium ion NO 2 +:
HNO 3 + 2 H 2 SO 4 ⇔ H 3 O + + 2 HSO 4 - + NO 2 + (nitronium ion)
- Nitronium ion attacks benzene:
C 6 H 6 + NO 2 + → C 6 H 6 NO 2 +
- Nitrobenzene is formed:
C 6 H 6 NO 2 + + HSO 4 - → C 6 H 5 NO 2 + H 2 SO 4
In summary:
C 6 H 6 + HNO 3 → C 6 H 5 NO 2 + H 2 O
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 C 6 H 5 NH 2, 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
C 6 H 5 NO 2 → C 6 H 5 NO → C 6 H 5 NHOH → C 6 H 5 NH 2
Nitrobenzene reduction to obtain aniline. Benjah-bmm27. Source: Wikimedia Commons.
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
C 6 H 5 NHOH → HOC 6 H 4 NH 2
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.
Sometimes it is possible to medicate children with fever with acetaminophen. Acetaminophen is a derivative of nitrobenzene. Author: Augusto Ordonez. Source: Pixabay.
Acetaminophen tablets, a derivative of nitrobenzene. Paracetamol_acetaminophen_500_mg_pills.jpg: Michelle Tribe from Ottawa, Canadaderivative work: Anrie. Source: Wikimedia Commons.
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.
C 6 H 5 –NO 2 + 3 CO + H 2 O → C 6 H 5 –NH 2 + 3 CO 2
In obtaining other chemical compounds
Nitrobenzene is the starting point to obtain a great variety of compounds used as colorants, pesticides, medicines and cosmetics.
Some colorants are obtained thanks to nitrobenzene. Author: Edith Lüthi. Source: Pixabay.
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
- Ingredient of mixes for polishing metals
- In soaps
- In mixtures for polishing shoes
- Preservative for spray paints
- Component of mixes for floor polishing
- Almond essence substitute
- In the perfume industry
- In the production of synthetic rubber
- Solvent in various processes
Nitrobenzene is part of some shoe polishing mixes. D-Kuru. Source: Wikimedia Commons.
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
Nitrobenzene contamination of the environment can occur through wastes 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 2.
With a solar reactor it is possible to eliminate water pollution with nitrobenzene. Mihai-Cosmin Pascariu. Source: Wikimedia Commons.
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
- US National Library of Medicine. (2019). Nitrobenzene. Recovered from pubchem.ncbi.nlm.nih.gov.
- Morrison, RT and Boyd, RN (2002). Organic Chemistry. 6th Edition. Prentice-Hall.
- Moldoveanu, SC (2019). Pyrolysis of Other Nitrogen-Containing Compounds. In Pyrolysis of Organic Molecules (Second Edition). Recovered from sciencedirect.com.
- Smith, PWG et al. (1969). Aromatic nitration-Nitro compounds. Electrophilic Substitutions. In Aromatic Chemistry. Recovered from sciencedirect.com.
- Windholz, M. et al. (editors) (1983). The Merck Index. An Encyclopedia of Chemicals, Drugs, and Biologicals. Tenth Edition. Merck & CO., Inc.
- Ullmann's Encyclopedia of Industrial Chemistry. (1990). Fifth Edition. Volume A22. VCH Verlagsgesellschaft mbH.
- 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.
- Shikata, T. et al. (2014). Nitrobenzene anti-parallel dimer formation in non-polar solvents. AIP Advances 4, 067130 (2014). Recovered from doaj.org.
- Krogul-Sobczak, A. et al. (2019). Reduction of Nitrobenzene to Aniline by CO / H 2 O in the Presence of Palladium Nanoparticles. Catalysts 2019, 9, 404. Recovered from mdpi.com.
- 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.