Dakin rearrangemnt

Dakin reaction

1. Presented by VIJAY S RA1932008010033 Subject: Advanced Organic Chemistry Subject code : 18PCY303 TOPIC : DAKIN REACTION DEPARTMENT OF CHEMISTRY

2. The 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(H 2 O 2 ) in base to form a benzenediol and a carboxylate . Overall , the carbonyl group is oxidized , and the hydrogen peroxide is reduced. The mechanism undergoes via aryl migration (rearrangement) , An electron-releasing group is necessary for efficient migration of aryl group . The Dakin reaction, which is closely related to the Baeyer- Villiger oxidation, and which are named after Henry Drysdale Dakin. DAKIN REACTION

3. R eagents Alkaline H 2 O 2 , Acidic H 2 O 2 , Peroxybenzoic acid(C 7 H 6 O 3 ), Peroxyacetic acid(C 2 H 4 O 3 ), Sodium percarbonate , 30 % H 2 O 2 with aryl selenium, Urea-H 2 O 2 adduct. Mechanis m : Step:1 Dakin reaction

4.   N ucleophilic   addition  of a hydroperoxide   anion  to the  carbonyl   carbon , forming a  tetrahedral intermediate 2 .Nucleophilic addition

5. 3 . 1,2 Shift The intermediate collapses,causing [1,2] aryl   migration,   hydroxide   elimination , and formation of a phenyl   ester

6. The phenyl ester is subsequently  hydrolyzed : nucleophilic addition of hydroxide from solution to the ester carbonyl carbon forms a second tetrahedral intermediate 4 .Hydrolysis

7. 5 .Phenoxide Ion Formation which collapses, eliminating a carboxylic acid   and forming a  phenoxide  

8. 6 .Abstration of proton Finally, the phenoxide extracts the  acidic   hydrogen  from the carboxylic acid, yielding the collected products

9. The Dakin oxidation has two  rate-limiting steps : nucleophilic addition of hydroperoxide to the carbonyl carbon and [1,2]-aryl migration. Therefore , the overall rate of oxidation is dependent on the nucleophilicity of hydroperoxide , the  electrophilicity  of the carbonyl carbon , and the speed of [1,2]-aryl migration. The   alkyl  substituents on the carbonyl carbon, the relative positions of the hydroxyl and carbonyl groups on the aryl ring, the presence of other functional groups on the ring, and the reaction mixture  pH  are four factors that affect these rate-limiting steps. Factors affecting reaction kinetics

10. In general, phenyl aldehydes are more reactive than phenyl ketones because the ketone carbonyl carbon is less electrophilic than the aldehyde carbonyl carbon. Alkyl substituents Relative positions of hydroxyl and carbonyl groups O - hydroxy phenyl aldehydes and ketones oxidize faster than  p - hydroxy phenyl aldehydes and ketones in weakly basic conditions.

11. In  o - hydroxy compounds, when the hydroxyl group is  protonated , an intramolecular  hydrogen bond  can form between the hydroxyl hydrogen and the carbonyl  oxygen , stabilizing a  resonance structure  with positive  charge  on the carbonyl carbon, thus increasing the carbonyl carbon’s electrophilicity . Lacking this stabilization, the carbonyl carbon of  p - hydroxy compounds is less electrophilic. Therefore ,  o - hydroxy compounds are oxidized faster than  p - hydroxy compounds when the hydroxyl group is protonated.

12. Other functional groups on the aryl ring Substitution  of phenyl hydrogens with  electron-donating groups   ortho  or  para  to the carbonyl group increases electron density at the migrating carbon, promotes [1,2]-aryl migration, and accelerates oxidation. Substitution with electron-donating groups  meta   to the carbonyl group does not change electron density at the migrating carbon; because unsubstituted phenyl group migratory aptitude is low , hydrogen migration dominates. Substitution with electron-withdrawing groups   ortho  or  para  to the carbonyl decreases electron density at the migrating carbon, inhibits [1,2]-aryl migration, and favors hydrogen migration

13. APPLICATION

14. Thank You