dr. sk mohammad aziz - narajole raj college

COMPILED AND CIRCULATED BY DR. SK MOHAMMAD AZIZ,

ASSISTANT PROFESSOR, DEPARTMENT OF CHEMISTRY, NARAJOLE RAJ COLLEGE

CHEMISTRY: SEM-IV, PAPER- C10T: ORGANIC CHEMISTRY-IV, REARRANGEMENT REACTION

Dr. SK MOHAMMAD AZIZ

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CHEMISTRY: SEM-IV, PAPER- C10T: ORGANIC CHEMISTRY-IV, REARRANGEMENT REACTION2

Molecular Rearrangements

Fries Rearrangement

Aryl esters with Lewis acid undergo rearrangement to give phenols having keto substituent at ortho and para positions. The complex between the ester and Lewis acid gives an acyliumion which reacts at the ortho and para positions as in Friedel-Crafts acylation.





Mechanism Fries Rearrangement

In general, low temperature favors the formation of para-product (kinetic control) and high temperature lead to the formation ortho-product (thermodynamic control).




Molecular RearrangementsFries Rearrangement

Example:




Molecular RearrangementsHofmann-Martius Rearrangement

The Hofmann–Martius rearrangement in organic chemistry is a rearrangement reactionconverting an N-alkylated aniline to the corresponding ortho and / or para aryl-alkylatedaniline. The reaction requires heat, and the catalyst is an acid like hydrochloric acid.

The reaction is also known to work for aryl ethers and two conceptually related reactionsare the Fries rearrangement and the Fischer–Hepp rearrangement. Its reactionmechanism centers around dissociation of the reactant with the positively chargedorganic residue R attacking the aniline ring in a Friedel–Crafts alkylation





Mechanism:

Hofmann-Martius Rearrangement





The conjugate acid of the amine releases nitrosonium ion which reacts at para-position to give the p-nitroso product.

This organic reaction was first described by the German chemist Otto Philipp Fischerand Eduard Hepp in 1886, and is of importance because para-NO secondary anilinescannot be prepared in a direct reaction. The rearrangement reaction takes place byreacting the nitrosamine precursor with hydrochloric acid. The chemical yield isgenerally good under these conditions, but often much poorer if a different acid is used.The exact reaction mechanism is unknown but there is evidence suggesting anintramolecular reaction.

Fisher-Hepp Rearrangement




Molecular RearrangementsFisher-Hepp Rearrangement

Mechanism:




Molecular RearrangementsN-azo to C-azo rearrangement

N-Arylazoanilines undergo rearrangement in presence of an acid to produce 4-(2-aryldiazenyl)aniline. On treatment with acid, aryldiazonium ion is formed from theconjugate acid of amine, which migrates to the para position almost selectively




Molecular RearrangementsBamberger rearrangement

Arylhydroxyamines with acid undergoes rearrangement to give aminophenols. Mechanismof this reaction is different from those described above. In this rearrangement, theconjugate acid of the hydroxylamine undergoes nucleophilic attack by the solvent.




Molecular RearrangementsOrton rearrangement

Treatment of N-chloroacetanilide with hydrochloric acid affords a mixture of orthoand para-chloracetanilides in the same proportions as in the direct chlorination ofacetanilide.




Molecular RearrangementsOrton rearrangement

Mechanism:




Molecular RearrangementsBenzidine Rearrangement

These compounds undergo [5,5]-sigmatropic rearrangement in the presence of acid to give benzidines.




Molecular RearrangementsMechanism: Benzidine Rearrangement





Home Task:

Predict the major products in the following reactions with mechanism





What products would you expect from the following reactions? Explain with mechanisms

Home Task:





Complete the following reactions with major products and mechanism

Home Task:

dr. sk mohammad aziz - narajole raj college

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