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Flashcards in Benzene Deck (7)
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Elec sub of benzene with nitric acid

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.


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

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


Bromination of benzene

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


Chlorination of benzene?

Electrophile; AlCl3/ FeCl3 --- Cl+ ion
Product : Chlorobenzene + HCL


Alkylation of benzene

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


Acylation of benzene

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


why are alkenes more reactive than arenes like benzene?

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