Fries Rearrangement – Different Rearrangement Reactions and Limitations

What is a Rearrangement in Organic Chemistry?

A rearrangement in organic chemistry is a process in which a molecule is rearranged to form a different molecule. This can be done through a variety of different reactions, including substitution, elimination, and pericyclic reactions. Each type of reaction can result in a different type of rearrangement.

Type of rearrangement.

Curtius Rearrangement or Curtius Reaction

• The Curtius rearrangement is an organic reaction in which an alkyl halide is converted to an alkyl aryl ketone. The reaction is named for its discoverer, the German chemist Ernst Curtius.
• The Curtius rearrangement occurs via an S2 mechanism. The alkyl halide is converted to the alkyl aryl sulfonate, which is then converted to the alkyl aryl ketone.

Claisen Rearrangement

• The Claisen rearrangement is an organic reaction that results in the conversion of an ester into an aldehyde or ketone. The reaction is named for the German chemist Emil Claisen, who first described it in 1888. The reaction is catalyzed by a strong base, such as sodium hydride, and it occurs in two steps.
• The first step is the formation of an enolate ion. The enolate is then attacked by the carbonyl group of the ester, and this results in the formation of a tetrahedral intermediate. The final step is the displacement of the leaving group, and this results in the formation of the aldehyde or ketone.

Beckmann Rearrangement

• The Beckmann Rearrangement is an organic reaction that results in the rearrangement of an aldehyde or ketone functional group into an alkene. The reaction is named for German chemist Max Beckmann, who first described it in 1905. The reaction is catalyzed by a base, typically sodium hydroxide or potassium hydroxide.
• The Beckmann Rearrangement occurs in two steps. The first step is the migration of a proton from the aldehyde or ketone functional group to the oxygen atom. This forms an enol intermediate, which is unstable and undergoes a second step to form the alkene.
• The Beckmann Rearrangement is an important reaction in the synthesis of alkene molecules. It can be used to convert aldehydes and ketones into the corresponding alkene molecules, which can then be used in further chemical reactions.

Hofmann Rearrangement

• The Hofmann Rearrangement is a chemical reaction in which a quaternary ammonium cation is converted into a tertiary amine. The reaction is named for Arthur Hofmann, who first described it in 1894.
• The Hofmann Rearrangement is a three-step process. In the first step, the quaternary ammonium cation is converted into a iminium ion. In the second step, the iminium ion is converted into a tertiary amine. In the third step, the tertiary amine is converted back into the quaternary ammonium cation.
• The Hofmann Rearrangement is used to convert quaternary ammonium cations into tertiary amines. Tertiary amines are more stable than quaternary ammonium cations, and they are less likely to undergo unwanted reactions. Tertiary amines are also more soluble in water than quaternary ammonium cations, making them more useful in chemical processes.

About Fries Rearrangement

The Fries rearrangement is a type of organic reaction in which a carbonyl group is rearranged to a hydroxyl group. The reaction is named for the German chemist Carl Fries, who first described it in 1836. The Fries rearrangement is a type of carbonyl-oxygen migration.

Fries Rearrangement Mechanism

• In the Fries rearrangement, an alkene undergoes a 1,2-shift of a hydrogen atom to form an alkane. This reaction is named for the Dutch chemist Jacobus Henricus van ‘t Hoff, who first proposed it in 1884.
• The Fries rearrangement is an example of an inversion of configuration. In this reaction, the carbon atom that was formerly attached to the hydrogen atom moves to the opposite side of the alkene molecule. This reaction can occur either through a concerted mechanism or through a stepwise mechanism.
• The stepwise mechanism is the more common mechanism, and it proceeds through a series of three steps. In the first step, the hydrogen atom is transferred from the carbon atom to the oxygen atom. In the second step, the carbon atom and the oxygen atom recombine to form an alkene. In the third step, the hydrogen atom is transferred back to the carbon atom.
• The concerted mechanism is less common, but it is more efficient. In this mechanism, the hydrogen atom is transferred from the carbon atom to the oxygen atom in a single step.

Limitations of Fries Rearrangement

The Fries rearrangement is limited to alkyl halides. The Fries rearrangement is a reaction that can be used to convert a ketone into an aldehyde with the use of a strong base. The reaction is named after the chemist Johannes Nicolaus Fries, who first reported the reaction in 1848. The reaction is favored by the presence of aprotic solvents, such as DMSO or DMF, and a strong base, such as sodium hydride. The reaction proceeds through the formation of an enolate anion, which is then attacked by the ketone. The reaction is generally considered to be irreversible, and the resulting aldehyde is often unstable.

Photo-Fries Rearrangement

• The photo-fries rearrangement is a type of rearrangement reaction that results in the formation of a new carbon-carbon bond. This reaction is named for the french fries pattern that is typically observed when the reaction is performed using infrared spectroscopy.
• The photo-fries rearrangement is typically performed using ultraviolet light. The reaction is initiated by the absorption of ultraviolet light by an electron-rich compound. This causes the compound to undergo a series of electron transfers, which leads to the formation of a new carbon-carbon bond.
• The photo-fries rearrangement is used to form carbon-carbon bonds in a variety of different compounds. It is particularly useful for the synthesis of bicyclic compounds.

Anionic Fries Rearrangement

• The anionic fries rearrangement is a rearrangement reaction that occurs when an alkyl halide is treated with an aqueous base. The alkyl halide is converted into an alkene and a primary or secondary amine.
• The mechanism of the anionic fries rearrangement is believed to involve an initial alkylation of the amine with the alkyl halide to form an imine. The imine then undergoes a 1,2-elimination reaction to form the alkene and the amine.
• The anionic fries rearrangement is named after French chemist Maurice Fries.