Name Reactions in Chemistry

1. 10/18/2020
1
Name Reactions
Dr. Satish Dhirendra Mitragotri
(M.Sc., Ph.D., SET, NET, GATE and M.B.A. (Finance))
Department of Chemistry
Walchand College of Arts and Science, Solapur
1
Name Reactions
Mechanism and applications of following reactions :
3.1 Stobbe condensation.
3.2 Oppenauer oxidation.
3.3 Meerwein Ponndorf Verley reduction.
3.4 Reformatsky reaction.
3.5 Wagner - Meerwein Rearrangement.
3.6 Hofmann rearrangement reaction.
3.7 Wittig reaction.
Related problems.
2
Nature of carbonyl group
Aldehydes have C=O bond which is polar in nature
Oxygen being more electronegative carries
negative charge where as carbon has partial
positive charge. The incoming nucleophile attacks
the carbon.
C
O
R1 H
C
O
R1 H
+
-
C
O
R1 H
+
-
B-
C
O
R1 H
-
B
3
Nature of carbonyl group
C
O
R1 R2
C
O
R1 CH2
H
B-
C
O
R1 CH2
C
O
R1 CH2
C
O
R1 CH2
Ketones on treatment with base generate carbanion
which is stabilized by resonance.
4
Hofmann rearrangement reaction.
Conversion of an amide into primary amine
with one carbon less by action of alkaline
hypohalite is called as Hofmann rearrangement
NH2
NaOBr (Br2 + NaOH)
- NaBr
NH2
Hofmann reaction
C
O
R
R
Amide
Amine containing one C less
5
Mechanism of reaction
Formation of Hypobromide
Formation of N-Bromoamide
Hofmann rearrangement reaction.
2 NaOH + Br2
NaOBr NaBr + H2O
+
Formation of Hypobromide
NH2
NH-Br
C
O
R
NaOBr
+ C
O
R
+ -OH
Amide N-Bromoamide
6

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Mechanism of reaction
Formation of N-Bromoamide anion and nitrene
intermediate
Formation of isocynate intermediate
Hofmann rearrangement reaction.
NH-Br N-Br N
C
O
R
+
-OH
C
R
O
C
R
O
Br
N-Bromoamide anion Nitrene
N
N N
C
R
O
C
R
O
+ C
R
O
Isocyanate Isocyanate
Nitrene
7
Mechanism of reaction
Addition of water to isocynate and Formation of
amine
Hofmann rearrangement reaction.
N
OH2
N
H
OH NH2 CO2
C
R
O
C
R
O
R +
CO2
Na2CO3 + H2O
2 NaOH
+
8
Applications
Hofmann rearrangement reaction.
NH2
NaOBr (Br2
+ NaOH)
- NaBr
NH2
C
O
CH3CH2
Amide
Amine containing one C less
CH3CH2
NH2
NaOBr (Br2 + NaOH)
- NaBr
NH2
N
N
C
O
Amide
Amine containing one C less
NH2
NaOBr (Br2 + NaOH)
- NaBr
NH2
NH2
NH2
C
O
Amide
9
Wagner-Meerwein Rrearrangement
Reactions involving the change in the carbon skeleton through
rearrangement of the carbonation intermediate are collectively
known as Wagner-Meerwein rearrangements.
Wagner-Meerwein rearrangement
CH3
CH3
CH3
CH2
Br
OH
CH3
CH3
CH3
CH2
OH CH3
OH
CH3
CH2
CH3
C
SN1
1-bromo, 2,2-dimethyl propane
C
2,2-dimethyl 1-propanol
Expected Product Obtained Product
C
2-methyl, 2-butanol
CH3
CH3
CH3
CH2Br
OH
CH3
OH
CH3
CH2CH3 CH3
CH3
CHCH3
C
SN1
C C
+
1-bromo, 2,2-dimethyl propane 2-methyl, 2-butanol 2-methyl, 2-butene
10
• Mechanism
Wagner-Meerwein Rrearrangement
CH3
CH3
CH3
CHCH3
OH
Br
CH3
CH3
CH3
CHCH3
CH3
CH3
CH3
CHCH3
CH3
CH3
CH3
CHCH3
OH
OH
- H
+
CH3
CH3
CH3
CCH3
C
SN1
C
+
C
+
Secondary carbocation Tertiary carbocation
C
C
11
Applications of WM reaction
Wagner-Meerwein Rrearrangement
CH3
CH3
CH3
CH2
OH
H2
SO4
CH3
CH3
CHCH3
CH2
CH3
CH2CH3
C C
2-methyl, 2-butene
+ C
2-methyl, 1-butene
2,2-dimethyl 1-propanol
OH CH2
H
+
Br
AgNO2
NO2
NO2
CH2
+
NH2
CH2
NaNO2 + HCl = HNO2
OH
CH2
OH
+
12

3. 10/18/2020
3
Stability of Carbocation is more important -As benzyl is
more stable than tertiary
Wagner-Meerwein Rrearrangement
OH
CH3
CH3
CH3
CH
OH
CH3
CH3
CH3
CH
Br
C CH3
CH3
CH3
CH
OH
C
CH3
CH3
CH3
CH
OH
CH3
CH3
CH3
CH
OH
Expected Product
Obtained Product
SN1
C
+
C
+
C
13
Wittig Reaction
Synthesis of alkenes by the treatment of aldehydes or
ketones with Wittig reagent
(alkylidenetriphenylphosphorane) or phosphorane is
known as Wittig reaction.
This reaction is useful for generating alkene functional
group from variety of carbonyl groups like aldehyde,
ketones, ketenes, isocynates and nitroso functional
group.
Ph3P=CH2 C=O
R2
R1
C=CH2
R2
R1
Ph3P=O
+ +
14
The Wittig reagent i.e.
alkylidenetriphenylphosphorane can be
synthesized from triphenylphosphine with alkyl
halide to generat phosphonium salt which on
treatment with strong base like phenyl lithium
gives witting reagent.
Wittig Reaction
Ph3P CH3Br Ph3P CH3Br
C6H5Li
Ph3P CH2
Ph3P=CH2
+
+
+
15
Mechanism of Wittig reaction – Wittig reagent reacts
with carbonyl compound to produce cyclic BETAIN
intermediate which is decomposed to produce alkene
Wittig Reaction
Ph3
P CH2
O=C
R2
R1
Ph3
P CH2
R2
R1
Ph3
P CH2
R2
R1
Ph3
P CH2
R2
R1
+ +
O C
O C
Betain
O
C
16
• Applications of Wittig reaction
Wittig Reaction
O CH2
Ph3P CH2 Ph3P O
+
+
O Ph3P C(CH3)2
C(CH3)2
Ph3P O
+
+
C=O
R2
R1 Ph3P CH-CH2COOCH3
C=
R2
R1
CH-CH2COOCH3
Ph3
P O
+
+
17
Applications of Wittig reaction
Wittig Reaction
Ph3P C(R)2
R2C=C=O R2C=C=C(R)2
R-N=C=O
R-N=C=C(R)2
R-N=O
R-N=C(R)2
Ketene
+
Nitroso
Isocynate
18

4. 10/18/2020
4
Reformatsky Reaction
Reaction of alpha haloesters with aldehydes or ketones
in presence of metallic Zinc in dry benzene solvent to
produce beta hydroxy esters is known as Reformatsky
reaction
Mechanism
1.Insertion of metallic Zn to C-Br bond to form organometallic
compound
Br-CH2
-COOC2
H5
Zn + Benzene
H+ , H2
O
C=O
R2
R1
C
R2
R1
OH
CH2-COOC2H5
+
Alpha bromo ester
Beta hydroxy ester
Br-CH2
-COOC2
H5 Zn
Benzene
CH2-COOC2H5
I2
Zn
+ Br
19
2.This is followed by formation of carbanion and its salt
3.The carbanion attacks carbonyl carbon to produce oxonium ion
which on decomposition with water produces beta hydroxy
ester.
Reformatsky Reaction
H2
O, H+
HO Zn Br C
R2
R1
OH
CH2-COOC2H5
Beta hydroxy ester
C
R2
R1
O
CH2
-COOC2
H5
Zn Br
+
CH2-COOC2H5
Zn
C=O
R2
R1
Br
+
+
+
Hydrolysis
+
20
• Under acidic condition beta hydroxy compound
decomposes to produce alph-beta unsaturate ester
which can yield alpha-beta unsaturated acid on
hydrolysis.
Reformatsky Reaction
C=O
H
Br-CH2-COOC2H5
Zn + Benzene
H+ , H2
O
C
OH
CH2-COOC2H5
H
H+ , H2
O C CH-COOC2H5
H
C CH-COOH
H
+
Dehydration
Beta hydroxy ester
Alpha beta unsaturated ester
Cinnamic acid
21
Applications of Reformatsky reaction
•Synthesis of alph-beta unsaturated esters
• Elongation of carbon chain
Reformatsky Reaction
Br-CH2-COOC2H5
Zn + Benzene
H+ , H2O
C CH-COOC2H5
H
C=O
H
O
O
+
Alpha beta unsaturated ester
OH
C=O
CH3CH2
CH3
Br-CH2
-COOC2
H5
Zn + Benzene
H+ , H2O
C
CH3CH2
CH3
CH2-COOC2H5
C
CH3CH2
CH3
CH-COOC2H5
CH
CH3CH2
CH3
CH2-COOH
Dehydration
+
Hydrolysis
Reduction H2 + Pd
22
Stobbe Reaction
Base catalyzed reaction of aldehydes or ketones with
dialkyl esters of succinic acid to produce alpha-beta
unsaturated esters is known as Stobbe reaction.
Mechanism of reaction.
Base catalyzed formation of anion
(CH3
)3
COOK
C=O
R2
R1
C
R2
R1
CH2
-COOK
CH2
-COOC2
H5
CH2
-COOC2
H5
(CH3)3COH
COOC2H5
C
+
Diethy ester of succinic acid
Alpha Beta unsaturated ester
(CH3)3COOK
(CH3)3C-OH CH2-COOC2H5
CH-COOC2
H5
CH2-COOC2H5
CH2
-COOC2
H5
23
• Attack of carbanion on carbonyl carbon followed by attack of
oxonium ion on ester carbonyl group to form cyclic
intermediate
Stobbe Reaction
C
R2
R1
O
CH2
C-COOC2
H5
C
O
C=O
R2
R1
CH2
-COOC2
H5
CH-COOC2
H5
- OC2
H5
(CH3
)3
COOK
OC2
H5
C
R2
R1
O
CH2
CH-COOC2H5
C
O
C
R2
R1
O
CH2
C-COOC2
H5
C
O
C
R2
R1
CH2
-COOK
COOC2
H5
C
Alpha Beta unsaturated ester
+
24

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5
• Applications
Synthesis of alpha-beta unsaturated acid
Stobbe Reaction
C=O
H
H
+
H
H
(CH3
)3
COOK
(CH3
)3
COH
CH2-COOC2H5
CH2-COOC2H5
C CH2-COOK
COOC2H5
C
H
C CH2
-COOK
COOH
C
H
C CH2-COOH
C
+
Decarboxylation
Hydrolysis
25
• Synthesis of polycyclic compounds
Stobbe Reaction
CH2
H2
SO4
C CH-COOH
C O
CH3 (CH3
)3
COOK
(CH3
)3
COH
CH2
-COOC2
H5
CH2
-COOC2
H5
CH3
C
O
HO
CH3
HO
COOH
+
26
M P V Reduction
C
O
R1 R2 CH3
CH3
C
OH
H
Al[OCH(CH3
)2
]3
CH3
CH3
C
O
C
OH
R1 R2
H
+ +
Meerwein Ponndorf Verley Reduction – Reduction of
aldehydes or ketones to alcohols on treatment with
alumimium isoproposide in excess of isopropyl alcohol is
known as M P V reduction
This is reversible reaction so the reaction is driven in the forward
direction by removing product of reaction i.e. ketone by
distillation process.
The reaction occurs under mild conditions and it is fast.
Other functional groups like C=C, NO2, CN etc. are not affected
during reaction.
27
Mechanism
M P V Reduction
C
O
R1 R2
Al[OCH(CH3
)2
]2
CH3
CH3
C
O
H
Al[OCH(CH3
)2
]2
CH3
CH3
C
O
R1
R2
C
O
H
Al[OCH(CH3
)2
]2
CH3
CH3
CH3
CH3
C
OH
H
- Al[OCH(CH3)2]3
+
C
O
R1
R2
C
O
H
+
C
OH
R1
R2 H
28
Mechanism involves formation of a cyclic transition
state in which hydride ion from alpha C-H bond of the
alkoxide migrates to carbonyl carbon to give mixed
alkoxide.
The excess of isopropyl alcohol is exchanged to liberate
the reduced ketone.
The transfer of hydride ion from isopropoxide is proved
by using Al(ODCMe2)3
It has great synthetic importance as this is chemo
selective reduction reaction .
M P V Reduction
29
Applications
Al[OCH(CH3)2]3
HOCH(CH3)2
CH2=CH-CHO
CH2
=CH CH2OH
Allyl alcohol
Acrealdehyde
M P V Reduction
Al[OCH(CH3)2]3
HOCH(CH3
)2
CH3
-CH=CH-CHO CH3-CH=CH CH2OH
Crotonaldehyde Crotyl alcohol
CH3
Al[OCH(CH3)2]3
HOCH(CH3)2
CH3
C
O
C
OH
H
30

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Applications
M P V Reduction
H
NO2
Al[OCH(CH3
)2
]3
HOCH(CH3
)2
NO2
H
C
O
C
OH
H
Al[OCH(CH3
)2
]3
HOCH(CH3
)2
O OH
31
Oxidation of secondary alcohols with ketone and base
such as alumimium tertiary butoxide or potassium
tertiary butoxide is known as Oppenaure oxidation.
Commonly ketone like acetone, cyclohexanone are
used in the reaction.
Oppenaure Oxidation
Al[OC(CH3)3]
C
OH
H
R1 R2 CH3
CH3
C
O
CH3
CH3
C
OH
H
R1 R2
C
O
+ +
32
Mechanism of reaction involves traction between
alcohol and aluminium tertiary butoxide to form the
aluminium derivative of secondary alcohol . This
derivative forms a cyclic transition state which
undergoes internal hydride ion transfer, resulting in
oxidation of alcohol.
This is also chemoselective reaction in which other
functional groups like C=C, RCOOR’, NH2, etc. remain
unchanged.
This reaction has many synthetic applications.
Oppenaure Oxidation
33
Oppenaure Oxidation
Al[OCH(CH3
)2
]2
CH3
CH3
C
OH
H
R1 R2
Al[OC(CH3)2]
CH3
CH3
CH3
CH3
CH3
Al[OC(CH3)2]
CH3 CH3
C
O
Al[OC(CH3)3]
+
C
O
R1
R2
C
O
H
+
C
OH
R1
R2 H
C
O
C
O
R1
R2
C
O
H
34
Applications
CH2=CH CH2
OH CH2=CH-CHO
Al[OC(CH3)3]
O=C(CH3)2
Allyl alcohol Acrealdehyde
Oppenaure Oxidation
CH3-CH=CH-CHO
CH3-CH=CH CH2
OH Al[OC(CH3)3]
O=C(CH3)2
Crotyl alcohol Crotonaldehyde
CH3
C
O
CH3
C
OH
H
Al[OC(CH3
)3
]
O=C(CH3
)2
35
• Applications
Oppenaure Oxidation
O
OH
Al[OC(CH3
)3
]
O=C(CH3
)2
Al[OC(CH3
)3
]
O=C(CH3
)2
NO2
H
C
OH
H
H
NO2
C
O
36

7. 10/18/2020
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How will you bring out following transformation
CH3
C
H3
CH3
CH2CONH2
CH3
C
H3
CH3
CH2NH2
NaNO2 + HCl
CH3
C
H3
CH2
CH3
- H+
?
?
?
+
?
+
?
O O
37