Fries Rearrangement
The fries rearrangement is a rearrangement reaction of a phenolic ester to a hydroxyl aryl ketone by using Lewis as catalysts.
The Fries rearrangement, named for the German chemist Karl Theophil Fries, is a rearrangement reaction of a phenolic ester to a hydroxy aryl ketone by catalysis o
The reaction is a ortho and para selective and one of the two product can be favoured by changing the reaction condition, such as Temperature and solvent.
The Fries rearrangement is a classic organic reaction that converts phenyl esters into hydroxyaryl ketones using a Lewis acid catalyst (typically aluminum chloride, AlCl₃). This reaction is widely used in the synthesis of pharmaceuticals, fragrances, and UV stabilizers.
Mechanism of Fries Rearrangement
Step 1: Lewis Acid Coordination
AlCl₃ binds to the ester carbonyl oxygen, activating the carbonyl carbon.
Step 2: Acylium Ion Formation
The C-O bond cleaves, generating reactive species
Step 3: Electrophilic Aromatic Substitution
The acylium ion attacks the aromatic ring:
- Ortho attack (favored at >100°C)
- Para attack (favored at 25°C):
Step 4: Rearomatization
Proton loss yields the final product.
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Applications of Fries Rearrangement
1. Synthesis of Hydroxyaryl Ketones
- Fries rearrangement is a direct route to compounds like hydroxyacetophenones, which are precursors in pharmaceuticals, perfumes, and dyes.
2. Pharmaceutical Industry
- Used in the synthesis of non-steroidal anti-inflammatory drugs (NSAIDs) such as paracetamol analogs.
- Helps in preparing intermediates for various antibacterial and anti-inflammatory agents.
3. Production of UV Stabilizers and Antioxidants
- Many hydroxyaryl ketones derived from Fries rearrangement are used in manufacturing UV absorbers and antioxidants in plastics and rubbers.
4. Perfume Industry
- Aromatic ketones like 4-hydroxyacetophenone are important fragrance ingredients or used in the synthesis of aroma compounds.
5. Synthesis of Agricultural Chemicals
- Used to create intermediates in the manufacture of pesticides and herbicides.
6. Materials Chemistry
- Starting materials for the synthesis of high-performance polymers, especially where aromatic ketones provide thermal and mechanical stability.
Photo-Fries rearrangement
The Photo-Fries Rearrangement is a photochemical version of the Fries rearrangement, in which aryl esters are rearranged under UV light to give hydroxyaryl ketones (ortho- and para-isomers). Unlike the classical Fries rearrangement that uses Lewis acids, the photo-Fries rearrangement proceeds through radical intermediates.
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