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 ofbOppenauer Oxidation

Dakin Reaction

Dakin reaction) is an organic redox reaction in which an ortho– or para-hydroxylatedbphenyl 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.

Also, Visit:

B. Pharma Notes | B. Pharma Notes | Study material Bachelor of Pharmacy pdf

B. Pharma Handwritten Notes

B. Pharma PDF Books

B. Pharma Lab Manual

D. Pharma Lab Manual

B. Pharma 8th Semester Previous Year Question Paper

D. Pharma Notes

Leave a Comment