Benzene

Question 1

Elec sub of benzene with nitric acid

Answer 1

H atom on benzene ring is replaced by a NO2+ electrophile (produced by HN03 +H2SO4) produces Water and H2SO4- ion .

Catalyst ; H2SO4

Heated to 50 DC for good rate of reaction. (if higher then further sub reactions will occur leading to production of dinitrobenzene)

catalyst is regenerated by reaction between H+ and HSO4- ion.

Question 2

Halogenation of benzene , what are the conditions necessary for all halogenation reactions of benzene?

Answer 2

A halogen carrier catalyst is needed - common carriers include ; FeBr (Bromination) , FeCL3 (chlorination) , AlCL3 (for Chlorination, alkylation, acylation)

Question 3

Bromination of benzene

Answer 3

electrophile ; AlBr3 — Br+ Bromonium ion.
Why? Cuz Benzene is too stable to react with a non-polar Br2 molecule.
product ; Bromobenzene + H^+

Question 4

Chlorination of benzene?

Answer 4

Electrophile; AlCl3/ FeCl3 — Cl+ ion

Product : Chlorobenzene + HCL

Question 5

Alkylation of benzene

Answer 5

sub of H atom on benzene by an alkyl group- occrs by reacting benzene with a haloalkane in presence of AlCl3

e.g ; benzene + C2H5Cl = Ethylbenzene +HCL

Question 6

Acylation of benzene

Answer 6

sub of H atom on benzene by acyl chloride using catalyst AlCl3
e.g ;
benzene + Ethanol chloride = Phenylethanone + HCL

Question 7

why are alkenes more reactive than arenes like benzene?

Answer 7

alkenes hae a pi bond/s which contain localised electrons above and below plane of two carbon atoms in double bond = are of high e density.

localised e in pi bond induce a dipole in the non-polar bromine molecule making one bR2 molecule slightly polarised = act like an electrophile

benzene cannot gain electrophiles by electro addition because of delocalised pi electrons spread above and below the plane of the Carbon atoms in the ring structure = less electron density in benzene ring than c-c double bond