Claisen-Schmidt condensation, Clemmensen reduction, Wolff rearrangement, Oppenauer-oxidation and Dakin reaction, and Birch reduction.

1. REACTION
SEM- IV
NAME
Compiled By- Dr. Atul© Dr. Atul R. Bendale

2. CLAISEN–
SCHMIDT
CONDENSATION
7
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3. Mechanism
Reaction
© Dr. Atul R. Bendale
The reaction between an aldehyde or ketone having an alpha-hydrogen with an aromatic carbonyl compound lacking an alpha hydrogen
is called the Claisen–Schmidt condensation.
- In cases where the product formed still has reactive alpha hydrogen and a hydroxide adjacent to an aromatic ring, the reaction will quickly
undergo dehydration leading to the condensation product.
The deprotonation of acetone by
hydroxide ion gives the enolate ion.
Which was used further as nucleophile
The acetaldehyde enolate ion attack to
the benzylic carbon of benzaldehyde via
nucleophilic addition to form the
intermediate as shown in
This is the formation of an aldol In the
basic condition, the hydroxide ion tends to
remove one proton from the α-carbon
resulting the formation of C=C double
bond at the α and β carbon. At the same
time, the hydroxide group attached to the
β carbon forms a leaving group. After the
condensation, benzalacetone was formed
after two water molecules leaved
General mechanism of synthesis of dibenzal acetone via
Claisen–Schmidt condensation

4. CLEMMENSEN
REDUCTION
8
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5. Reaction
© Dr. Atul R. Bendale
Reduction to hydrocarbon: Carbonyl group of compound is reduced to methylene group by using zinc amalgam and hydrochloric
acid.This reaction is called Clemmensen reduction. In this reaction carbonyl group is reduced to –CH2- group. Ketones are more
effective than aldehydes in this reduction. The mercury alloyed with the Zn does not participate in the reaction; it serves only to provide
aclean active metal surface. Some times alcohols may be used as the solvent in Clemmensen reduction.
An AMALGAM is an alloy of mercury with another metal, which may be a liquid, a soft paste or a solid, depending upon the proportion of mercury. These
alloys are formed through metallic bonding, with the electrostatic attractive force of the conduction electrons working to bind all the positively charged
metal ions together into a crystal lattice structure. Almost all metals can form amalgams with mercury, the notable exceptions being iron, platinum, tungsten,
and tantalum. Silver-mercury amalgams are important in dentistry, and gold-mercury amalgam is used in the extraction of gold from ore.
Electrophilic addiction of H to
carbonyl carbon followed by attack
of Zn to carbonyl carbon
Electrophilic addiction of H to
carbonyl carbon followed by attack
of Zn to carbonyl carbon
With Attack of Cl, ZnCl leaves the
reaction, forming carbanion
Electrophilc attack followed by
repetation of step 2 on further
protonation gives Alkane
Mechanism

6. WOLFF-KISHNER
REDUCTION
9
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7. MechanismReaction
Wolff-Kishner reduction: Reaction of an aldehyde or ketone with excess hydrazine generates a hydrazone derivative, which is heated with
Sodium ethoxide at 1800C, Nitrogen is eliminated and carbonyl group is converted to methylene group
Step 1: Deprotonation of Nitrogen
Step 2: Protonation of the Carbon
Step 3: Deprotonation of Nitrogen
Step 4: Protonation of Carbon
The Wolff-Kisher reduction is used to convert ketones to methylene
groups, and aldehydes to methyl groups. It cannot be used to reduce
the carbonyl groups of amides and esters.
- Wolff-Kishner vs. Clemmensen Reductions
*Clemmensen reduction is done for aldehyde or ketones in presence of
Zn-Hg (Zinc amalgam)/Conc. HCl to form alkane. This reaction occurs
on the zinc metal surface. There are two types of mechanism for these
reactions. A. Cabanionic mechanism, B. Cabenoid mechanism.
*WOlff-Kishner reduction is also for aldehyde/ ketones in presence of
hydrazine (N2H4),KOH,H2O and 180 °C temperature to form alkane

8. OPPENAUER
OXIDATION
1
0
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9. 0
Mechanism
Reaction
© Dr. Atul R. Bendale
Oppenauer Oxidation is the process of conversion of secondary alcohols to ketones by selective oxidation. Oxidation
reaction takes place in the presence of [(CH3)3CO]3 Al] in excess of acetone. It is an aluminium alkoxide catalyzed the oxidation of a
secondary alcohol to the corresponding ketone. This is reverse of the Meerwein Ponndorf Verley reduction. It is a very good
method to oxidise allylic alcohols to α, β- unsaturated ketones.
Similarly two more moles of acetone will react with above (one
mole) formed complex and give two more moles of ketone
product.
Here exchange reaction takes place.
Aluminium complex gets
deprotonated by an alkoxide ion, to
generate an alkoxide intermediate
The substrate alcohol are bound to the
aluminium. The acetone is coordinated to
the aluminium which activates it for the
hydride transfer from the alkoxide. The
aluminium-catalyzed hydride shift from
the α-carbon of the alcohol to the
carbonyl carbon of acetone proceeds
over a six-membered transition state
Coordinates to the aluminium to
form a complex.
The desired ketone is formed after
the hydride transfer

10. DAKIN
REACTION
1
1
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11. 0
Mechanism
Reaction
© Dr. Atul R. Bendale
The Dakin oxidation (or Dakin reaction) is an organic redox reaction in which an ortho- or para-hydroxylated phenyl aldehyde (2-
hydroxybenzaldehyde or 4-hydroxybenzaldehyde) or ketone reacts with hydrogen peroxide in base to form a benzenediol and
a carboxylate. Overall, the carbonyl group is oxidized, and the hydrogen peroxide is reduced.
eliminating a phenoxide and
forming a carboxylic acid . Finally,
the phenoxide extracts the acidic
hydrogen from the carboxylic
acid, yielding the products
The Dakin oxidation starts
with nucleophilic addition of a
hydroperoxide anion to
the carbonyl carbon, forming
a tetrahedral intermediate
The intermediate collapses,
causing [1,2]-aryl migration,
hydroxide elimination, and
formation of a phenyl ester,
which is hydrolyzed: nucleophilic
addition of hydroxide from
solution to the ester carbonyl
carbon forms a second
tetrahedral intermediate

12. BIRCH
REDUCTION
1
2
© Dr. Atul R. Bendale

13. 0
Mechanism
Reaction
© Dr. Atul R. Bendale
The Birch reduction is an organic reaction where aromatic rings undergo a 1,4-reduction to provide unconjugated cyclohexadienes. The
reduction is conducted by sodium or lithium metal in liquid ammonia and in the presence of an alcohol.
The mechanism begins with a single electron transfer(SET) from the metal to the aromatic ring, forming a radical anion. The anion then
picks up a proton from the alcohol which results in a neutral radical intermediate. Another SET, and abstraction of a proton from the
alcohol results in the final cyclohexadiene product and two equivalents of metal alkoxide salt as a byproduct.
Animation
In the last step a second proton leads
the cyclohexadienyl carbanion to
the unconjugated cyclohexadienyl
product. These steps are outlined
below for the case of anisole.
The solution of metal in ammonia
provides electrons which are
taken up by the aromatic ring to
form the corresponding radical
anion B in the first step of the
reaction
This is followed by protonation by
the alcohol to form a
cyclohexadienyl radical C. Next, a
second electron is transferred to
the radical to form a
cyclohexadienyl carbanion D

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