Benzene
Created by:
Tomáš Machula
Filák Antonín
Benzene
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Benzene, also known as C6H6, PhH, and benzol, is an organic chemical
compound which is a colorless and flammable liquid with a pleasant,
sweet smell.
Benzene is a known carcinogen. It is a component of gasoline. It is an
important industrial solvent and precursor in the production of drugs,
plastics, gasoline, synthetic rubber, and dyes.
Benzene is a natural constituent of crude oil, but it is usually synthesized
from other compounds present in petroleum.
Benzene is an aromatic hydrocarbon, and the second [n]-annulene ([6]annulene).
gasoline - benzín
dyes – barviva
rubber – guma
crude - surový
Properties of Benzene
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General
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Systematic name Benzene
Other names Benzol
Molecular formula C6H6
Molar mass 78.11 g/mol
Appearance Colorless liquid
CAS number [71-43-2]
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Hazards
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R-phrases R45, R46, R11, R36/38,
R48/23/24/25, R65
S-phrases S53, S45
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Properties
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Density and phase 0.8786 g/cm³
Solubility in water 1.79 g/l (25 °C)
Melting point 5.5 °C (278.6 K)
Boiling point 80.1 °C (353.2 K)
Viscosity 0.652 cP at 20 °C
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Structure
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Molecular shape Planar
Dipole moment 0 D
History
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Benzene was discovered in 1825 by
the English scientist Michael Faraday,
who isolated it from oil gas and gave
it the name bicarburet of hydrogen.
In 1833, the German chemist Eilhard
Mitscherlich produced it via the
distillation of benzoic acid (from gum
benzoin) and lime. Mitscherlich gave
the compound the name benzin. In
1845, the English chemist Charles
Mansfield, working under August
Wilhelm von Hofmann, isolated
benzene from coal tar. Four years
later, Mansfield began the first
industrial-scale production of
benzene, based on the coal-tar
method.
Michael Faraday
Production
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Benzene may result whenever carbon-rich materials
undergo incomplete combustion. It is produced naturally in
volcanoes and forest fires, and is also a component of
cigarette smoke.
Up until World War II, most benzene was produced as a
byproduct of coke production in the steel industry. However,
in the 1950s, increased demand for benzene, especially
from the growing plastics industry, necessitated the
production of benzene from petroleum. Today, most
benzene comes from the petrochemical industry, with only
a small fraction being produced from coal.
Three chemical processes contribute equally to industrial
benzene production: catalytic reforming, toluene
hydrodealkylation, and steam cracking.
Byproduct – vedlejší produkt
Uses
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In the 19th and early 20th centuries, benzene was used as an
aftershave because of its pleasant smell. Prior to the 1920s,
benzene was frequently used as an industrial solvent, especially
for degreasing metal. As its toxicity became obvious, other
solvents replaced benzene in applications that directly exposed
the user to benzene.
As a gasoline additive, benzene increases the octane rating and
reduces knocking. As a result, gasoline often contained several
percent benzene before the 1950s, when tetraethyl lead replaced
it as the most widely used antiknock additive. However, with the
global phaseout of leaded gasoline, benzene has made a
comeback as a gasoline additive in some nations. By far the
largest use of benzene is as an intermediate to make other
chemicals. The most widely produced derivatives of benzene are
styrene, which is used to make polymers and plastics, phenol for
resins and adhesives (via cumene), and cyclohexane, which is
used in Nylon manufacture. Smaller amounts of benzene are used
to make some types of rubbers, lubricants, dyes, detergents,
drugs, explosives and pesticides.
Health Effects
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Breathing very high levels of benzene can result in death, while
high levels can cause drowsiness, dizziness, rapid heart rate,
headaches, tremors, confusion, and unconsciousness. Eating or
drinking foods containing high levels of benzene can cause
vomiting, irritation of the stomach, dizziness, sleepiness,
convulsions, rapid heart rate, and death.
The major effect of benzene from chronic (long term) exposure is
to the blood. Benzene damages the bone marrow and can cause a
decrease in red blood cells leading to anemia. It can also cause
excessive bleeding and depress the immune system, increasing
the chance of infection.
The US Occupational Safety and Health Administration (OSHA)
has set a permissible exposure limit of 1 part of benzene per
million parts of air (1 ppm) in the workplace during an 8-hour
workday, 40-hour workweek.
Exposure – vystaveni
The End
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