Hell Volhard Zelinsky Reaction
Hell-Volhard-Zelinsky (HVZ) reaction is an organic reaction that is used to convert a carboxylic acid having at least one α-H atom to an α-halo carboxylic acid, using a red phosphorous catalyst, halogen gas, and water. HVZ reaction is a type of substitution reaction.
The reaction conditions for the Hell Volhard Zelinsky reaction are quite severe- involving reaction temperatures above 373 K and increased reaction time. The reaction usually requires less than one equivalent of phosphorous (or a PX3). Certain activated carboxylic acids and acid derivatives (e.g. anhydrides, acyl halides, 1,3-diesters) that are readily enolized can be halogenated in the absence of a catalyst.
1. Carboxylic acid is converted to acyl bromide.
2. Acyl bromide is tautomerize to its enol form
3. Bromination of the enol's alpha-carbon
4. Hydrolysis of α-bromo acid bromide to give α-bromoacid.
Step-1: Carboxylic acid is converted to acyl bromide by treatment with PBr3
Step-2: Acyl bromide is tautomerize to its enol form
Step-3: Bromination of the enol's alpha-carbon
Step-4: On hydrolysis of α-bromo acid bromide gives the final product α-bromo carboxylic acid
The reaction conditions for the Hell Volhard Zelinsky reaction are quite severe- involving reaction temperatures above 373 K and increased reaction time. The reaction usually requires less than one equivalent of phosphorous (or a PX3). Certain activated carboxylic acids and acid derivatives (e.g. anhydrides, acyl halides, 1,3-diesters) that are readily enolized can be halogenated in the absence of a catalyst.
Mechanism of Hell Volhard Zelinsky Reaction
Mechanism of Hell Volhard Zelinsky Reaction takes place in the following four steps-1. Carboxylic acid is converted to acyl bromide.
2. Acyl bromide is tautomerize to its enol form
3. Bromination of the enol's alpha-carbon
4. Hydrolysis of α-bromo acid bromide to give α-bromoacid.
Step-1: Carboxylic acid is converted to acyl bromide by treatment with PBr3
Step-2: Acyl bromide is tautomerize to its enol form
Step-3: Bromination of the enol's alpha-carbon
Step-4: On hydrolysis of α-bromo acid bromide gives the final product α-bromo carboxylic acid
