Reimer Tieman Reaction
The Reimer–Tiemann reaction is a classic organic reaction used to convert phenols into hydroxy aldehydes. This happens when phenols react with chloroform (CHCl₃) in the presence of a strong base such as sodium hydroxide (NaOH) or potassium hydroxide (KOH).
This reaction mainly places a –CHO (formyl) group at the ortho-position of the phenol. If the ortho positions are blocked, the group shifts to the para-position. Because the reaction introduces a formyl group through substitution, it is classified as an electrophilic substitution reaction.
Mechanism (Explained Simply)
The reaction follows these key steps:
- Formation of Dichlorocarbene
Chloroform reacts with strong alkali to generate a reactive species called dichlorocarbene (CCl₂). This carbene acts as the electrophile in the reaction. - Attack by Phenoxide Ion
In basic medium, phenol becomes phenoxide ion, which is more reactive. This phenoxide attacks the dichlorocarbene, forming an intermediate called benzylidene dichloride. - Hydrolysis of Intermediate
The intermediate undergoes hydrolysis (reaction with water) to produce hydroxybenzaldehyde — usually salicylaldehyde (ortho product).
Overall, the reaction provides a useful method to introduce a –CHO group onto an aromatic ring.
Applications
- Used to synthesize salicylaldehyde, an important starting material for dyes and perfumes.
- Helps in preparing key intermediates for pharmaceutical compounds.
- Useful for converting phenols into more reactive building blocks for organic synthesis.
Additional Notes
The reaction proceeds through a unique carbene intermediate, making it important for understanding carbene chemistry and electrophilic aromatic substitution involving unusual electrophiles.
Detailed Notes:
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