1
Aromatic chemistry and Toluene
For HS(12)
C-32(part-2)
2
Equal moles of aryl halide and alkyl halide
dissolved in dry ether when reacts with Na
produces alkyl benzene
Wurtz-Fittig reaction
Cl
+ 2Na + Cl-CH 3
Dry ether
CH 3
+ 2NaCl
Disadvantage : biaryl and alkanes are side products
Ar-X + 2Na + X-Ardry ether
Ar-Ar + 2NaX
R-X + 2Na + X-R dry ether
R-R + 2NaX
3
• When phenyl magnesium bromide/iodide reacts with methyl bromide/iodide in dry ether produces toluene
Using Grignard reagent
MgBr
+ CH 3BrDry ether
CH 3
+ MgBr2
Benzyl magnesium chloride on hydrolysed by dil HClProduces toluene
CH 2MgCl
dil HCl
CH 3
+ MgCl2
4
• In Friedel-Crafts alkylation, treatment of benzene with an alkyl halide and a Lewis acid (AlCl3) forms an alkyl benzene( when R = -CH3, toluene forms)
Friedel-Crafts Alkylation
+ CH 3Cl Anh AlCl3
CH 3
Polyalkylation is the main disadvantage of this reaction.
5
From tolueic acid & p-toluidine
CH 3
COONa
+ NaOHCaO
Heat
CH 3
Sodium salt of tolueic acid
CH 3
NH 2
p-toluidine
HCl/NaNO 2
00C
CH 3
N=NCl
H 3PO 2
CH 3
6
1.Insoluble in water
2.Soluble in alcohol in ether
3.Lighter than water
4.Used as solvent
Physical properties
7
-CH3 gr is ortho para orienting, so –CH3 directs o/p
position for incoming group.
(a) Ring chlorination (b) side chain chlorination
Chemical properties-chlorination
(a)
CH 3
+ Cl2Fe dust
CH 3 Cl
+
CH 3
Clo-chloro toluene
p-chloro toluene
Ring chlorination should be done at ordinary temperature in pr of halogen carrier I2 or anh AlCl3 or FeCl3 of Fe dust
8
Bromine reacts similar way that of chlorine
Bromination
CH 3
+ Br2
Fe or FeBr3+
CH 3
BrCH 3
Br
9
Condition : boiling toluene or in pr of UV light
Reaction : H atoms in –CH3 gr substituted by –Cl
atom one by one….to form benzyl chloride, benzal
chloride and benzotrichloride.
Sidechain chlorination
CH 3
C l2
1100C
CH 2Cl
Cl2
1100C
CHCl2
Cl21100C
CCl3
10
Benzyl chloride on hydrolysis gives benzylalcohol,
benzalcloride gives benzaldehyde and benzo tri chloride
gives benzoic acid.
Hydrolysis of side chain chlorinated product
CH 2Cl
+ NaO H
CH 2O H
CHCl2
+ Ca(O H)2
C O H
O H
H
-H 2O
CHO
CCl3
+ Ca(O H)2
H 2O
1500C
C O H
O H
HO CO O H
-H2O
11
Side chain bromination
CH 3
NBS(1 m ole)
sunlight
CH 2Br
12
At ordinary condition 1:1 mixture of conc HNO3 and
conc H2SO4 react with toluene to form orto and para
nitro toluene
Nitration of toluene
conc HNO 3
conc H 2SO 4
+
CH 3CH 3 CH 3
NO 2
NO 2
When the above mixture is heated at 60-800C it gives 2,4-dinitro toluene
13
At ordinary condition 1:1 mixture of fuming HNO3
and fuming H2SO4 react with toluene to form 2,4,6
trinitro toluene
Preparation of TNT
Mixture of TNT and ammonium nitrate is known as amatol
fum ing HNO 3
fum ing H 2SO 4
CH 3 CH 3
NO 2
NO 2
O 2N
TNT
14
Toluene when heated with conc sulphuric acid
produces ortho and para toluene sulphonic acid.
Sulphonation
conc H 2SO 4
CH 3 CH 3
SO 3H
+
CH 3
SO 3H
Ortho product predominates at lower temp but para product predominates at higher temperature.
Heat
15
Toluene when reacted with methyl chloride and anh
AlCl3, ortho xylene and para xylene form
Friedel craft reaction
CH 3
CH 3Cl
anh AlCl3+
CH 3CH 3
CH 3
CH 3
16
(i) Etard reaction : Toluene when oxidised by chromyl
chloride in CS2 of CCl4 at room temperature produces a
complex which subsequently hydrolysed to form
benzaldehyde.
Oxidation of toluene
CH 3
(i) CrO 2Cl2
(ii) H 2O
CHO
+ H 2O
17
(ii) chromic acid in acetic anhydride oxidises toluene into
benzaldehyde which immediately conveted to benzylidine
di acetate which hydrolysed by dil H2SO4 produces
benzaldehyde
Oxidation of toluene
CH 3
CrO 3
(CH 3CO)2O
CH
OCOCH 3
OCOCH 3
dil H 2SO 4
CHO
+ 2CH 3COOH
Benzylidine di acetate prevents the oxidation of benzaldehyde to benzoic acid
18
(iii) Toluene when reacted with MnO2 + moderately conc
H2SO4 at 400C produces benzaldehyde
Oxidation of toluene
CH 3CHO
M nO 2
H 2SO 4
+ M nSO 4 + H 2O
If acid is concentrated and temperature is high , the product of the above reaction will be benzoic acid.
19
(iv) Toluene when reacted with alkaline KMnO4 or acidic
K2Cr2O7 produces benzoic acid
Oxidation of toluene
We can also use air passed over V2O5(cat) at 3000C with toluene vapour produces benzoic acid
CH 3
KMnO 4
NaOH
COONa
H +
COOH
K 2Cr2O 7 + H 2SO 4
20
Toluene vapours when reacted with H2 passed over
finely devided Ni ( cat) at 180-2000C forms methyl
cyclohexane.
Hydrogenation of toluene
CH 3
+ 3H 2
Ni
2000C
CH 3
21
Aromatic chemistry and Chlorobenzene
For HS(12)
C-32(part-2)
22
In presence of Fe or FeCl3 at ordinary temperature,
benzene reacts with chlorine gas to form chlorobenzene
preparation of chlorobenzene
Cl2
Fe or FeCl3
Cl
+ HCl
In presence of excess chlorine o- and p- dichloro benzene results
23
In industry, chlorobenzene is prepared by passing a
mixture of benzene vapour, HCl and air over Cu2O as
catalyst at 2500C
Indutrial method(Rasching process)
Cl
HCl
1/2 O 2, Cu2O
2500C
+ H 2O
24
Benzene diazonium chloride disolved in HCl when
heated with cuporus chloride produces chlorobenzene
From benzene diazonium chloride
Second step of the above reaction is known as Sandmeyer reaction.
NH 2
NaNO 3+ HCl
00C
N=N-Cl
CuCl/HCl
Cl
+ N 2 + HCl
25
Other preparations:
O H
+ PCl5
Cl
+ PO Cl3 + HCl
+ HO Cl H +
Cl
+ H 2O
26
The Low Reactivity of Halobenzenes The Low Reactivity of Halobenzenes• The p orbital on the carbon atom of the
benzene ring side-way overlaps with the p orbital of halogen atom
form a delocalized bonding system
27
The Low Reactivity of Halobenzenes The Low Reactivity of Halobenzenes• The CX bond of halobenzenes is stronger
than that of haloalkanes
partial bond character
Breaking of the CX bond requires a larger amount of energy
substitution reactions of halobenzenes are difficult to occur
28
At 3000C and 300 atm pressure chlorobenzene reacts
with NaOH to form sodium phenate which on acidification
produces phenol
Replacement by –OH group
C l
+ 2NaOH 3000C
300 atm
ONa
dil HCl
OH
29
Replacement by –NH2 and –CN gr
Cl
+ 2NH 3Cu2O
2000C, 60 atm
NH 2.HCl
NaO H
NH 2
CuCN
Pyridine, 2000C
CN
+ CuCl
Or KNH2 in liq NH3 at -330C
30
At 1000C chlorobenzene react with a mixture of conc
HNO3 and conc H2SO4 to form a mixture of o-and p-
chloronitrobenzene
Nitration reaction
Cl
conc HNO 3
conc H 2SO 4
1000C
+
Cl Cl
NO 2
NO 2
31
Halogenation and sulphonation
Cl
Cl2
Fe or FeCl3+
ClCl
Cl
Cl
conc H 2SO 4
Cl
SO 3H
+
Cl
SO 3H
O- and p- chlorobenzenesulphonic acid
600C
32
F.C. alkylation & acylation
Cl
+ CH 3Cl anh
A lCl3 +
Cl ClCH 3
CH 3CO Cl
anh AlCl3+
Cl Cl
CO CH 3
CO CH 3
o- and p- chloroactophenone
o- and p- chlorotoluene
CH 3
33
DDT is produced when a mixture of chlorobenzene and
chloral is heated with conc H2SO4
Preparation of DDT
Cl
2 + O =C-CCl3
H
Cl
Cl
C CCl3
H
DDT
34
Preparation of biphenyl
C l
2 + 2Na ether
+ 2NaCl (W urtz reaction)
I
2 + Cu + CuI2 (U llm ann reaction)
35
Equal moles of aryl halide and alkyl halide
dissolved in dry ether when reacts with Na
produces alkyl benzene
Wurtz-Fittig reaction
Cl
+ 2Na + Cl-CH 3
Dry ether
CH 3
+ 2NaCl
Disadvantage : biaryl and alkanes are side products
36
Different conversions from chlorobenzene
Cl
M g in dry ether
M gCl
CH 2 CH 2
O
, H 3O +
C 6H 5CH 2CH 2O H
HCHO
H 3O +
C 6H 5CH 2O H
CH 3CHO
H 3O +
C 6H 5-CH
CH 3
O H
CH 3CN
H 3O +
C 6H 5CO CH 3
CO 2
H 3O +
ether m edium
C 6H 5CO O H
37
Aromatic chemistry and Nitrobenzene
For HS(12)
C-32(part-2)
38
Nitrobenzene is obtained by the action of a mixture of
Conc HNO3 and conc H2SO4 on benzene at 50-600C. At
higher temperature meta dinitrobenzene forms
Lab method
+ HO -NO 2
H 2SO 4
600C
NO 2
+ H 2O
In place of nitrating m ixture,we can use (a) conc HNO 3 of sp gr 1.5
(b)Fum ing nitric acid( containing 6-12% NO 2)
(c) Nitronium tetrafluoroborate ( NO 2+BF 4
-)
(d) Acetyl nitrate ( CH 3CO O NO 2)
39
Other preparation
C 6H 5N=N-ClHNO 2
Cu2OC 6H 5NO 2
HBF 4C 6H 5N 2
+BF 4- NaNO 2
Cu, heatC 6H 5NO 2
C 6H 5NH 2 + 3CF 3COO OH C 6H 5NO 2 + 3CF 3COO HTrifluoro per acetic acid
40
Nitrobenzene is very stable compound not easily
attacked by acids or alkalis but it is easily reduced.
There are two types of reactions of nitrobenzene :
(i) Reaction at nitro group (ii) Recation at benzene
nucleus
Chemical properties
41
Nitrobenzene when heated with Sn or Zn with conc
HCl or Fe dust + conc HCl or SnCl2/HCl, it is reduced to
aniline.
Reduction in acidic medium :
NO 2
Sn /HCl(C)
NH 2
+ 2H 2O
42
Nitrobenzene when warmed with powdered Zn and
NaOH( in methanol) converted to azoxy benzene.
Reduction in alkaline medium
NO 2
+
O 2NZn
m ethanolicNaOH
N=N
O
+
Azoxy benzene is further reduced to azobenzene with conc m ethanolic NaOH solution
N=N
O
+ Zn
m ethanolic NaOH
N=N
43
Nitrobenzene is reduced to hydrazo benzene when
treated with Zn dust and hot aq NaOH solution
Reduction in alkaline medium :
NO 2
+
O 2NZn
aqNaO H
N- N
H H
44
Nitrobenzene is reduced to phenyl hydroxylamine
when it is warmed with Zn dust and an aq solution of
NH4Cl in presence of ethanol
Reduction in neutral medium :
NO 2
Zn
NH 4Cl
NHOH
+ H 2O
45
The presence of NO2 can be confirmed using this
test.The compound is heated with Zn + 50% aq
ethanolic solution of NH4Cl.After cooling it is reacted
with Tollen’s reagent and formation of grey or black
ppt of metallic Ag confirms –NO2 gr.
Mulleken Barker Test
NO 2
Zn
NH 4Cl
NHO H
+ H 2O
C 6H 5NHO H + 2[Ag(NH 3)2]+O H - C 6H 5NO + Ag + NH 3 + H 2O
46
Other reductions :
Catalytic hydrgenation :
NO 2
+ H 2
raney Ni
NH 2
heat + 2H 2O
Electrolysis in weakly acidic m edium :
NO 2
+ 6H + + 6e
NH 2
Electrolysis in strongly acidic m ediumusing Ni electrodes :
NO 2
+ 4H + + 4e
NHOH
intram olecularrearrangem ent
NH 2
OH
p-am inophenol
47
If we want to reduce one nitro gr of m-dinitrobenzene,
the reducing agent to be used : NH4HS or aq Na2S or
methanolic NaHS or SnCl2 in HCl
Selective reduction
NO 2
NO 2
NH 4HS
NO 2
NH 2
m -nitroaniline
48
Substitution reactions
NO 2
Cl2
Fe powder
NO 2
Cl
Br2
Fe
NO 2
Br
conc HNO 3
conc H 2SO 4
900C
NO 2
NO 2
fum ing sulphuric acid
heat
NO 2
SO 3H
49
Nucleophilic substitution
NO 2
KO H
air
NO 2
OH
NO 2
O H
+
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