How to get benzene from hexane
Clear, colorless and light
Occurrence Hard coal, petroleum
|molar mass 78.112 g / mol |
AGW N / A, carcinogenic substance
density 0.8788 g / cm3
Melting point +5.538 ° C
boiling point +80.08 ° C
Conc. At 20 ° C 1.8 g / l
Refractive index (20 ° C) 1,5011
Explosion limit 1.2 to 7.8% by volume (air)
Flash point −11 ° C
Ignition point +498 ° C
|Hazard classes + category|
Flammable liquids 2
Skin corrosion / irritation 2
Serious eye damage / irritation 2
Germ cell mutagenicity 1A
Specific target organ toxicity w. 1
Aspiration hazard 1
|HP rates (see also note)|
H 225, 304, 315, 319, 340, 350, 372, 412
P 210, 260,280.1-4,6,7, 301 + 310, 305 + 351 + 338, 308 + 313, 403 + 233
disposal G 1
|German designation |
|English designation |
|CAS 71-43-2||benzene |
Note for schools: Benzene is a highly carcinogenic substance. It must not be kept or used in the school laboratory. Since benzene is contained in car gasoline as an anti-knock agent, it must not be used in chemistry classes in schools.
Effect on the human body
Benzene vapors are very toxic when inhaled. Symptoms include dizziness, vomiting, and loss of consciousness. The liquid can also be absorbed through the skin and in this way causes severe poisoning. With a benzene content of two percent by volume in the breath, death occurs after five to ten minutes. Chronic poisoning caused by ingestion of small amounts over a long period of time leads to damage to the bone marrow, liver and kidneys. Benzene can cause leukemia and is considered a strong carcinogen.
Benzene is a clear, easily mobile liquid that is highly refractive with a refractive index of 1.5011. Benzene hardly mixes with water, when mixed it floats due to its lower density. Ethyl alcohol, diethyl ether, gasoline, fats, resins, phosphorus and iodine can be easily dissolved in benzene.
The benzene in this bottle floats on top of one
Water layer, it is more refractive than water.
In the air, the hydrocarbon benzene burns with a sooty flame to form CO2 and H2O. Due to the high heat of combustion produced and its property of preventing pre-ignition in the gasoline engine - the "knocking" - it is used as an additive in unleaded petrol.
Benzene gives off a lot of soot when burned.
Because of its benzene ring in the molecular structure, benzene is the simplest representative of aromatics. The addition of halogens succeeds with UV light: If six chlorine atoms are added on the benzene ring, hexachlorocyclohexane is obtained, which forms various diastereomers: γ-hexachlorocyclohexane has become known under the name lindane. It is an insecticide that is difficult to break down in nature and that accumulates in the food chain.
The hydrogen atoms on the benzene ring can be substituted with halogens in the presence of iron (III) chloride: chlorine produces liquid chlorobenzene, which is used as a solvent and is required for the synthesis of phenol. With nitrating acid, a mixture of fuming nitric acid and concentrated sulfuric acid, one obtains nitrobenzene, an important intermediate in the production of aniline. In the case of renewed nitration, dinitrobenzene and trinitrobenzene can also be produced. All nitrobenzenes are highly toxic, trinitrobenzene is an explosive substance.
Nitrobenzene can also be used to make azobenzene. This intermediate product for the synthesis of azo dyes is obtained, for example, by reducing nitrobenzene with lithium aluminum hydride. This creates the typical azo group -N = N-. Azobenzene forms orange-red leaflets that hardly dissolve in water, but dissolve well in alcohol.
Dinitrobenzene and azobenzene from an old collection of chemicals
Mesomerism in the benzene molecule
There are theoretically two possibilities for the representation of the benzene molecule. The mesomerism arrow and the bracket make it clear that the two boundary structures shown do not really exist:
Since the bond distance between a single bond and a double bond is different, an irregular hexagon should result. With the help of the X-ray structure analysis, however, it can be calculated that the bond lengths between all carbon atoms in benzene are the same. The electrons are therefore distributed in a ring shape in the electron clouds, they are delocalized and align a symmetrical structure. The ring in the representation of the benzene molecule makes this clear. According to Pauling's hybrid orbital model, there are π bonds. This phenomenon of delocalized electrons is called Mesomerism or resonance. It occurs in numerous other inorganic and organic compounds, including nitrous oxide. The concept of resonance for chemical bonds goes back to Pauling.
Benzene is used in motor fuels as an additive to increase the knock resistance. It is the starting material for many organic and aromatic compounds such as nitrobenzene, aniline, phenol, styrene, insecticides such as lindane or DDT, azo dyes, plastics and synthetic resins. Benzene is also used in detergent production. It is an excellent, but unfortunately highly toxic, solvent for paints, resins, waxes and oils. Cheap shoes manufactured abroad may contain benzene residues if adhesives containing benzene have been used.
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