Dakin Reaction & Oppenauer Oxidation

Dakin Reaction & Oppenauer
Oxidation

Session Objectives

By the end of this
session, students will be able to:

• Dakin Reaction

Mechanism of Dakin
Reaction

Oppenauer
Oxidation

Mechanism of
Oppenauer Oxidation

Dakin Reaction

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.

Reaction Mechanism of Dakin
Reaction

The Dakin
reaction 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.

The
phenyl ester is subsequently hydrolyzed: nucleophilic addition of hydroxide
from solution to the ester carbonyl carbon forms a second tetrahedral intermediate,
which collapses, eliminating a phenoxide and forming a carboxylic acid.

Finally,
the phenoxide extracts the acidic hydrogen from the carboxylic acid, yielding
the collected products

Dakin Reaction

Dakin Reaction

Reaction Mechanism of Dakin
Reaction

Reaction Mechanism of Dakin Reaction

Synthetic applications of
Dakin reaction

The Dakin
reaction is most commonly used to synthesize benzenediols and alkoxyphenols.

Catechol,
for example, is synthesized from o-hydroxy and o-alkoxy phenyl
aldehydes and ketones, and is used as the starting material for synthesis of
several compounds, including the catecholamines, catecholamine derivatives, and
4-tert-butylcatechol, a common antioxidant and polymerization inhibitor.

Other
synthetically useful products of the Dakin reaction include guaiacol
(2-Methoxyphenol (a precursor of several flavorants; hydroquinone
(benzene-1,4-diol or quinol) a common photograph-developing agent; and 2-tert-butyl-4-hydroxyanisole
and 3-tert-butyl-4-hydroxyanisole, two antioxidants commonly used to
preserve packaged food.

In addition,
the Dakin reaction is useful in the synthesis of indolequinones, naturally
occurring compounds that exhibit high anti-biotic, anti-fungal, and anti-tumor
activities.

Oppenauer Oxidation

Oppenauer
oxidation
, named
after Rupert Viktor Oppenauer,is a gentle method for selectively oxidizing
secondary alcohols to ketones.

Oppenauer Oxidation

Alcohols
on refluxing with aluminium isopropoxide in acetone are oxidisied to aldehydes
or ketones.

Acetone
acts as hydrogen acceptor and it is converted into isopropyl alcohol.

The
presence of excess of acetone drives the reaction towards
the
oxidation product.

Reaction Mechanism of
Oppenauer Oxidation

Reaction Mechanism of Oppenauer Oxidation

Synthetic applications of Oppenauer Oxidation

• The Oppenauer oxidation is used to prepare analgesics in
the pharmaceutical industry such as morphine and codeine.

• For instance, codeinone is prepared by the Oppenauer
oxidation of codeine.

Synthetic applications of Oppenauer Oxidation

The
Oppenauer oxidation is also used to synthesize hormones.

Progesterone
is prepared by the Oppenauer oxidation of pregnenolone.

Synthetic applications of Oppenauer Oxidation

Summary

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.

Oppenauer
oxidation
, named
after Rupert Viktor Oppenauer, is a gentle method for selectively oxidizing
secondary alcohols to ketones.

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