Post on 22-Jan-2016
description
transcript
Reactions of arenes
L.O.:
Outline the mechanism of nitration. Outline the mechanism of of acylation. Identify the reactive intermediates involved
in nitration and acylation. Name the mechanisms of both reactions.
C C
C
CC
C HH
H H
H H
STRUCTURE OF BENZENE
STRUCTURE OF BENZENE
STRUCTURE OF BENZENE
NITRATION
+ HNO3 + H2O
NO2
nitrobenzene
Conditions conc HNO3
conc H2SO4 catalyst
50ºC
-H+
Formation of electrophile
HNO3
+ 2 H2SO4 + 2 HSO4-
+ H3O+
NO2
+
Reaction of electrophile with aromatic compound
NO2
NO2+ NO2
+H
nitronium ion
NITRATION – ELECTROPHILIC SUBSTITUTION
NITRATION
Equation (name product)
Conditions
Mechanism
CH3CH3
NO2
NITRATION
2-methylnitrobenzene
Conditions conc HNO3
conc H2SO4 catalyst
50ºC
CH3
+ HNO3 + H2O
CH3
NO2
NITRATION
Uses of nitro compounds:
1) as explosives
2) to make aromatic amines (used to make dyes)
CH3
NO2
NO2
O2N
1,3,5-trinitrotolueneTNT
Name the mechanism for this reaction.
Electrophilic substitution
Draw the electron arrangement (dot-cross diagram) of aluminium chloride.
FRIEDEL-CRAFTS ACYLATION
aromatic ketone
Conditions AlCl3 catalyst
R C
O
Cl+
CR O
+ HCl
+
CR O
+ R C
O
O C
O
R R C
O
OH
FRIEDEL-CRAFTS ACYLATION
WARNING! - do not mix
Friedel-Crafts acylation & other acylations
(needs AlCl3)
Swap H on benzene ring
for acyl group
H H N
H
R
H O R
Swap H on O/N
for acyl group
FRIEDEL-CRAFTS ACYLATION
WARNING! - Classic question to test this
NH2 NHCOCH3
CH3COCl
H replaced is on N not benzene ring.
This is NOT Friedel-Crafts acylation!
Formation of electrophile
AlCl3
+ RCOCl +
AlCl4–+
C
O
R
acylium ion
OR
AlCl3
+ R-C-O-C-R +
–
+
C
O
R
acylium ion
O
O R-C-O-AlCl3
O
FRIEDEL-CRAFTS ACYLATION – ELECTROPHILIC SUBSTITUTION
-H+
Reaction of electrophile with aromatic compound
CC
+H+
C
O
R
O
RO
R
FRIEDEL-CRAFTS ACYLATION – ELECTROPHILIC SUBSTITUTION
AlCl4– + H+ AlCl3 + HCl
+ H+ + AlCl3– R-C-O-AlCl3
O
R-C-OH
O
or
Regeneration of catalyst
Equation
Conditions
Mechanism
FRIEDEL-CRAFTS ACYLATION
CH3CH3
CO CH2CH3
Conditions AlCl3 catalyst
FRIEDEL-CRAFTS ACYLATION
CH3
CO CH2CH3
CH3
+ CH3CH2 C
O
Cl+ HCl