Chemistry OCR - A2 Benzene and Phenols

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Aisha Haque
Chemistry A2 Summer Project
Physical properties
Benzene is a colourless, mobile and volatile liquid. Its boiling point is 80°C and freezing point is 5.5°C. It has
characteristic odour.
It is highly inflammable.
It is lighter than water.
It is immiscible with water but miscible with organic solvents such as alcohol and ether.
Benzene itself is a good solvent. Fats, resins, rubber, etc. dissolve in it.
It is a non-polar compound and its dipole moment is zero.
It is an extremely poisonous substance. Inhalation of vapours or absorption through skin has a toxic effect.
Reactions and conditions
Benzene undergoes electrophilic substitution reactions, with strong electrophiles that are generated through the
addition of a halogen carrier. A hydrogen atom on the ring is replaced by the electrophile, this differs from alkenes
because they have localised pi-bonds whereas arenes / benzene has high stability because of the delocalised
structure of pi-bonds.
Nitration of benzene
Nitrations of benzene or arenes produce aromatic nitro compounds, which are important for the synthesis of
important products such as explosives and dyes.
Benzene is nitrated by concentrated nitric acid at 55 degrees Celsius in the presence of concentrated sulphuric acid
which acts as the catalyst. The sulphuric acid generates water and a nitronium ion NO2 + which is a strong enough
electrophile and can react with the benzene.
Bromination of arenes
Arenes react with bromine through electrophilic substitution which only takes place in the presence of a halogen
carrier which acts as a catalyst such as `Fe' and aluminium halides `AlCl3' chlorination and `AlBr3' for bromination .
`Fe' reacts with bromine to form `FeBr3' (iron III bromide) which is the halogen carrier, it then polarises Br2 molecule
creating Br+ and `FeBr4 ­', one Bromine atom replaces a hydrogen atom. HBr is generated when the replaced
hydrogen reacts with the halogen carrier.

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Uses and general importance
Benzene is used mainly as an intermediate to make other chemicals. About 80% of benzene is consumed in the
production of three chemicals, ethylbenzene, cumene, and cyclohexane. Its most widely produced derivative is
ethylbenzene, forerunner to styrene, which is used to make polymers and plastics. Cumene is converted phenol for
resins and adhesives. Cyclohexane is used in the manufacture of Nylon. Smaller amounts of benzene are used to
make some types of rubbers, lubricants, dyes, detergents, drugs, explosives, and pesticides.…read more

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Phenols take part in some typical acid reactions, reacting with sodium and bases to form ionic salts called phenoxides
releasing hydrogen gasses. Due to being a weak acid , phenols can also neutralise some alkali solutions forming a
phenol oxide and water.
Electrophilic substitution
Similarly to benzene phenols undergo electrophilic addition reactions but phenols can react at room temperature
without the need of a halogen carrier catalyst.…read more


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