Electrophillic Substitution Reactions of Benzene

Question 1

Nitration

Answer 1

Electrophile: NO2+ (nitronium ion)
Produces: nitrobenzene 
Warm benzene with concentrated sulphuric acid and nitric acid
H2SO4 + HNO3 --> H2NO3+ + HSO4-
H2NO3+ --> H2O + NO2+

Mononitration - keep below 55 degrees

Question 2

Sulfonation

Answer 2

Electrophile: sulphur trioxide
Produces: benzenesulfonic acid

1) Boil sulphuric acid and benzene under reflux for several hours
2) Warm benzene to 40 degress with fuming sulphuric acid for half an hour
* fuming H2SO4 is more richer in SO3

H2SO4 –> H20 + SO3

Substituted H+ bonds to lone pair on C-O oxygen atom

Question 3

Halogenation - chlorination

Answer 3

Benzene + chlorine + anhydrous AlCl3
Room temperature

Electrophile: Cl+ is produced as AlCL3 is a halogen carrier

Question 4

Halogenation - bromination

Answer 4

Benzene + bromine + FeBr3
Room temperature

Electrophile: Br+

Question 5

Alkylation

Answer 5

Friedal-crafts

Benzene + chloroalkane + halogen carrier (anhydrous)
Reflux

CH3Cl + AlCl3 –> CH3+ (carbocation) + AlCl4-

Question 6

Alcylation

Answer 6

Friedal-crafts

Benzene + acyl chloride + AlCl3 (anhydrous)
Reflux