1
May 16, 2015
1
2
AROMATICcompounds
Made by: AYESHA AFTAB MALIKBs in bioinformatics
International Islamic university Islamabad Pakistan
Aromatic compounds:
a hydrocarbon with alternating double an single bonds between carbon atoms
containing one or more benzene rings that are characteristic of the benzene series of compounds.
6
Benzene and Aromatic Compounds Benzene (C6H6) is the simplest aromatic
hydrocarbon (or arene). Benzene has four degrees of unsaturation,
making it a highly unsaturated hydrocarbon. Whereas unsaturated hydrocarbons such as
alkenes, alkynes and dienes readily undergo addition reactions, benzene does not.
History of aromatic compounds: August Wilhelm Hofmann
in 1855
August Kekulé in 1865
J. J. Thomson, between 1897 and 1906
Sir Robert Robinson, in 1925
Ernest Crocker in 1922
Hückel in 1931.
Physical properties of benzene
Benzene is a colorless, mobile and volatile liquid
It's boiling point is 80°C and freezing point is 5.5°C.
It has characteristic odor
It is highly inflammable and burns with sooty flame
It is lighter than water. It's specific gravity at 20°C is 0.8788
immiscible with water miscible with organic solvents such as alcohol and ether.
Benzene itself is a good solvent
It is a non-polar compound and its dipole moment is zero.
It is an extremely poisonous substance
Chemical properties of benzene
Bromination.Addition of bromine to benzene
.Ferric bromide or aluminum chlorite as a catalyst
Hydrogenation of benzene.Addition of hydrogen in
benzene .Ni as a catalyst
.300 c temp. and 30atm pressure
Nitration of Benzene.introduction of nitro group
.nitric or sulphuric acid as a catalyst
Chlorination of benzene.Addition of chlorine
.sunlight as a catalyst
Sulphonation of benzene.introduction of sulphonic
acid group
Friedal craft reaction
Friedal craft alkylation
Friedel–Crafts alkylation involves the alkylation of an aromatic ring with an alkyl halide using a strong Lewis acid catalyst. With anhydrous ferric chloride as a catalyst, the alkyl group attaches at the former site of the chloride ion
Alkyl group
any group derived from an alkane by the removal of one hydrogen atom. Alkyl groups are often designated by the symbol R.
General reactionwhere R= any alkyl group
Friedel craft Acylation
. Acylation means substituting an acyl group into something - in this case, into a benzene ring.
The most commonly used acyl group is CH3CO-. This is called the ethanoyl group
Acyl group
An acyl group is an alkyl group attached to a carbon-oxygen double bond. If "R" represents any alkyl group, then an acyl group has the formula RCO-
Friedal craft acylation
What is polycyclic aromatic hydrocarbon?
They consist of three or more benzene rings
commonly produced by fossil fuel combustion.
Also called polynuclear aromatic hydrocarbon.
Uses of Benzene
Tire/Rubber Manufacturing
Petroleum/Oil/Asphalt
Chemicals/Plastic
Auto Repair
Printing/Painting
Health hazards
What Products Have High Levels of Benzene?
Cigarettes Styrofoam(use mostly in food
containers) Cumene (paint thinner, lacquer thinner,
brush cleaner, paint stripper and spray paint) Benzene in Soft Drinks
Gasoline