Reaction of Benzene Flashcards
what are benzenes similar to
alkenes
what type of reactions do alkenes undergo
electrophilic addition
since benzenes are similar to alkenes, what type of reaction do we expect them to have
electrophilic addition
what type of reaction do benzenes actually undergo
electrophilic substitution
why do benzenes undergo electrophilic substitution
Because they have a delocalised ring of Π electrons so benzene react with
electrophiles and benzenes dont generally undergo addition reactions because these would involve breaking up
the delocalised system. Most of Benzene’s reactions involve substituting one H for another atom or group of atoms.
what benefit is there of benzene undergoing electrophilic substitution
this maintains the delocalised ring and it’s stability
what is a halogen carrier
a Lewis acid that can bind to a halogen molecule
what is the role of a hydrogen carrier for the reaction
it catalyses the reaction
what is a lewis acid
a substance to generate an electrophile for the benzene reactions
examples of lewis acids are
AlCl3, FeBr3
what are the 6 benzene reactions
bromination, chlorination, nitration, hydrogenation, Friedel-Crafts Alkylation and Friedel-Crafts Acylation
what is the reagent for the bromination of benzene
bromine
what are the conditions for the bromination of benzene
Warm under reflux with Fe/FeBr3 catalyst
what is the electrophile needed for the bromination of benzene
Br+
what is the electrophile formation for bromination
FeBr3 + Br2 → FeBr4− + Br+
what is the reagent for the chlorination of benzene
chlorine
what are the conditions for the chlorination of benzene
Warm under reflux with AlCl3/FeCl3 catalyst
what is the electrophile needed for the chlorination of benzene
Cl+
what is the electrophile formation for chlorination
AlCl3 + Cl2 → AlCl4− + Cl+
FeCl3 + Cl2 → FeCl4− + Cl+
what is the observation for the chlorination of benzene
Steamy White Fumes of HCl
what is the reagent for the nitration of benzene
nitric acid
what are the conditions for the nitration of benzene
Warm below 55oC, In presence of Concentrated Sulfuric Acid
what is the electrophile needed for the nitration of benzene
NO2 +
what is the electrophile formation for nitration
HNO3 + 2H2SO4 → NO2+ + 2HSO4− + H3O+
if temp for nitration is below 55oC how many NO2 groups are added
1
if temp for nitration is above 55oC how many NO2 groups are added
multiple
what is the reagent for the hydrogenation of benzene
hydrogen
what are the conditions for the hydrogenation of benzene
Heated at 2000C and 30atm in presence of Ni Catalyst.
what does the hydrogenation of benzene form
cyclohexane
what is cyclohexane used for
production of nylon in industry
what is a Friedel-craft reaction
what is Friedel-Crafts Alkylation of Benzene
Benzene can have a hydrogen substituted for an alkyl chain
what is the reagent used for alkylation of benzene
chloroalkane
what is the conditions used for alkylation of benzene
Warmed under reflux in presence of anhydrous AlCl3 catalyst
what is the electrophile needed for the alkylation of benzene
R+, the alkyl chain
what is the electrophile formation for the alkylation of benzene
AlCl3 + R-Cl → AlCl4− + R+ (where R is the alkyl chain)
what is Friedel-Crafts Acylation of Benzene
Benzene can have a hydrogen substituted for an acyl chain in the following reaction
what is the reagent used for acylation of benzene
Acyl chloride
what is the conditions used for acylation of benzene
Warmed under reflux in presence of anhydrous AlCl3 catalyst
what is the electrophile needed for the acylation of benzene
RCO+, alkyl chain and carbonyl group
what is the electrophile formation for the acylation of benzene
AlCl3 + R-COCl → AlCl4− + R-CO+ (where R is the alkyl chain)
what is a phenol
a benzene ring which has an OH group attached to it
is a phenol more or less recative than benzene
more
why cna the benzene ring be described as ‘activated’ in a phenol
because it can
polarise electrophiles more readily meaning reactions can occur in milder conditions and without
catalysts.
what 2 types of recations do phenols go through
bromination and nitration
what is the reagent for the bromination of phenol
bromine
what is the condition for the bromination of phenol
room temp
what does the bromination of phenol produce
a white ppt of 2,4,6-tribromophenol
what is the electrophile for the bromination of phenol
Br+
how does the bromination of phenol differ from benzene
doesnt need a catalyst andit undergoes multiple substitutions
what is the reagent for the nitration of phenol
dilute nitic acid
what is the condition for the nitration of phenol
room temp
what is the electrophile for the nitration of phenol
NO2+
what does the nitration of phenol produce
mixture of 2-nitrophenol and 4-nitrophenol
