Nitrobenzene

Structural formula
General
Surname	Nitrobenzene
other names	Mononitrobenzene Nitrobenzene Benzaline Mirban oil Mirban essence (false bitter almond oil)
Molecular formula	C 6 H 5 NO 2
Brief description	colorless to pale yellow, highly refractive liquid with a bitter almond oil odor
External identifiers / databases
CAS number 98-95-3 EC number 202-716-0 ECHA InfoCard 100.002.469 PubChem 7416 Wikidata Q407290
properties
Molar mass	123.11 g mol −1
Physical state	liquid
density	1.20 g cm −3 (20 ° C)
Melting point	6 ° C
boiling point	211 ° C
Vapor pressure	0.3 h Pa (20 ° C) 0.47 hPa (30 ° C) 1.9 hPa (50 ° C)
solubility	poor in water (1.9 g l −1 at 20 ° C) miscible with ethanol , benzene and diethyl ether
Refractive index	1.5530
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary danger H and P phrases H: 360F-301 + 311 + 331-351-372-412 P: 201-273-280-302 + 352-304 + 340-308 + 310
Authorization procedure under REACH	of particular concern : toxic for reproduction ( CMR )
MAK	not classified, as a suspected carcinogenic effect Switzerland: 0.2 ml m −3 or 1 mg m −3
Toxicological data	640 mg kg −1 ( LD 50 ,  rat ,  oral )
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Nitrobenzene is the simplest aromatic organic nitro compound . It was first presented in 1834 by Eilhard Mitscherlich . Nitrobenzene is liquid at room temperature and is stable in acidic and predominantly in alkaline environments. It is poisonous and suspected of causing cancer.

Extraction and presentation

Nitrobenzene is technically nitration of benzene using mixed acid produced. By dehydrating nitric acid with concentrated sulfuric acid, it initially forms reactive nitronium ions .

${\displaystyle \mathrm {H_{2}SO_{4}+HNO_{3}\rightarrow HSO_{4}^{-}+H_{2}O+NO_{2}^{+}} }$

The resulting nitronium ion (also known as nitryl cation) reacts with the benzene:

${\displaystyle \mathrm {NO_{2}^{+}+C_{6}H_{6}\rightarrow C_{6}H_{5}NO_{2}+H^{+}} }$

Nitrobenzene is formed, the free proton attaches itself to a water molecule ( oxonium ) and remains in solution with the hydrogen sulfate ion and may have to be neutralized.

properties

Physical Properties

Nitrobenzene is a colorless liquid , sometimes pale yellow due to impurities . It smells like bitter almond oil ( like " marzipan "), although there is a slightly pungent note, and tastes pleasantly sweetish marzipan-like in an aqueous solution . It's poisonous and flammable. Nitrobenzene has a high refractive index . Under normal conditions it has a density of 1.20 g / cm ³ , melts at 5.7 ° C and boils at 210.85 ° C; the flash point is 88 ° C. Nitrobenzene is only soluble in traces in water, but it can be mixed well with alcohols, ethers and benzene. Nitrobenzene dissolves poorly in dilute sulfuric acid, but completely from a concentration of 80%. The solubility is little dependent on temperature.

Chemical properties

The nitro group is inert to acids , electrophilic reagents and most oxidizing agents . But it reacts with Grignard reagents and strong bases . The strong −I and −M effects of the nitro group greatly reduce the electron density of the aromatic π system, which makes electrophilic aromatic substitutions more difficult, but favors nucleophilic aromatic substitutions . The heat of decomposition determined by DSC is −214 kJ mol ⁻¹ or −1740 kJ kg ⁻¹ .

Reactions

Nitrobenzene can be hydrogenated to aniline with hydrogen via nickel contacts at elevated temperature and pressure .

The technical reduction using iron powder in an alcoholic hydrochloric acid solution also produces aniline. If a nitrobenzene derivative is present that contains other reducible groups, the nitro reduction can be carried out selectively with tin (II) chloride in concentrated hydrochloric acid. The reduction of a nitro group of doubly nitrated aromatics can be carried out with sodium or ammonium sulfide .

If the chemical reduction is carried out in a neutral medium, phenylhydroxylamine is obtained . If a basic reaction medium is selected, different coupled compounds are obtained, depending on the reducing agent : with As ₂ O ₃ in aqueous sodium hydroxide solution, azoxybenzene is obtained , with zinc powder in alcoholic sodium hydroxide solution, azobenzene is obtained, and hydrazine in alcoholic sodium hydroxide solution with transition metal catalysts gives hydrazobenzene .

use

Nitrobenzene as a fuel
Brief description	Component of former racing fuels, ignition accelerators for diesel fuels, solvents
properties
Physical state	liquid
Flash point	88 ° C
Ignition temperature	480 ° C
Explosive limit	1.8-40% by volume
Temperature class	T1
Explosion class	IIB
safety instructions
UN number	1662
Hazard number	60
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Nitrobenzene is an important, large-scale intermediate in the manufacture of various chemicals such as aniline , benzidine , dinitrobenzene , trinitrobenzene , nitrobenzenesulfonic acid , fuchsine or quinoline .

To a small extent, nitrobenzene is also used as a solvent, lubricating oil component, chemical reagent and as an additive in explosives. It can also be used as an ignition accelerator for diesel fuels.

In the past, nitrobenzene was also used to perfume soaps under the name "Mirbanöl". The use in cosmetic products is now prohibited. “Mirban oil” was also used to disinfect collections of insects .

Due to the very pronounced magneto-optical effect of nitrobenzene of causing polarization rotations of the light when high voltage is applied, the substance in the Kerr cell is used to modulate light rays. In the past, a major application of the nitrobenzene-filled Kerr cells was to optically expose the sound on film material. In this context, the term Karolus cells is used instead of Kerr cells.

Biological importance

Nitrobenzene is harmful to the environment. It has water hazard class 2 (hazardous to water).

poisoning

Nitrobenzene can enter the human body through the skin, respiratory and digestive organs. There it can cause severe poisoning . The human blood turns dark brown and it loses the ability to absorb oxygen because methemoglobin is formed.

As a result, the blood turns bluish and cyanosis occurs. In addition, there is severe damage to the central nervous system and feelings of weakness, headaches and vomiting occur. In the case of more severe poisoning, there are also clouding of consciousness, palpitations, cramps and finally unconsciousness. Serious poisoning can lead to death within a few hours. Alcohol increases the toxic effects of nitrobenzene.

Small children and infants in particular are susceptible to poisoning with methaemoglobin formers such as nitrobenzene, as the corresponding enzymes for breaking down methaemoglobin are still missing.

As an antidote, ascorbic acid can be used in mild cases and toluidine blue in severe cases . Both drugs accelerate the reduction in methemoglobin. Toluidine blue results in a temporary, harmless blue coloration of the patient. Exchange transfusions can be used in life-threatening situations .

Individual evidence

1. ↑ ^{a b c d} Entry on nitrobenzene. In: Römpp Online . Georg Thieme Verlag, accessed on September 29, 2014.
2. ↑ ^{a b c d e f g h i j k l m n o p q} Entry on nitrobenzene in the GESTIS substance database of the IFA , accessed on April 16, 2018(JavaScript required) .
3. ↑ Entry on Nitrobenzene in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
4. ↑ Entry in the SVHC list of the European Chemicals Agency , accessed on August 19, 2016.
5. ↑ Swiss Accident Insurance Fund (Suva): Limit values ​​- current MAK and BAT values (search for 98-95-3 or nitrobenzene ), accessed on September 27, 2019.
6. ↑ Joachim Buddrus: Fundamentals of organic chemistry. 4th edition. Walter de Gruyter Verlag, Berlin 2011, ISBN 978-3-11-024894-4 , pp. 374-375.
7. ↑ T. Grewer, O. Klais: Exothermic decomposition - investigations of the characteristic material properties. (= Humanization of working life. Volume 84). VDI-Verlag, Düsseldorf 1988, ISBN 3-18-400855-X , p. 9.
8. ^ Fragrances [1]. In: Lueger, Otto: Lexicon of the entire technology and its auxiliary sciences, Vol. 7 Stuttgart, Leipzig 1909, pp. 425-426, on http://www.zeno.org . Contumax GmbH & Co. KG; Otto Lueger, 1909, accessed on May 17, 2019 : "For perfuming cheap toilet soaps" 
9. ↑ Gerfried Deschka: The disinfection of small collections of insects according to more recent points of view. In: Steyr Entomologenrunde. 21, Steyr 1987, pp. 57-61.
10. ↑ Heinz Lüllmann, Hein Lutz, Klaus Mohr, Martin Wehling: Pharmacology and Toxicology. Thieme, 2006, ISBN 3-13-368516-3 , pp. 507-508.