Theory and Defination :
Appel reaction is a type of organic reaction, which converts alcohol into an alkyl chloride by using chemical materials like tri-phenylphosphine and carbon tetra-halide(chloride or bromide).
The reason behind use of carbon tetrabromide or bromine as a halide source is to produce alkyl bromides, whereas other materials like carbon tetra iodide, methyl iodide or iodine gives alkyl iodides.
This Appel reaction is more or less similar to the one of the important chemicals reaction called Mitsunobu Reaction,in which combination of phosphine, a diazo compound acts as a coupling reagent, and a nucleophile is used to alter the stereo chemistry of an alcohol or displace it.
The reason behind use of carbon tetrabromide or bromine as a halide source is to produce alkyl bromides, whereas other materials like carbon tetra iodide, methyl iodide or iodine gives alkyl iodides.
This Appel reaction is more or less similar to the one of the important chemicals reaction called Mitsunobu Reaction,in which combination of phosphine, a diazo compound acts as a coupling reagent, and a nucleophile is used to alter the stereo chemistry of an alcohol or displace it.
Mechanism :
The reaction proceeds by activation of the tri-phenylphosphine by reaction with the tetra-halomethane, followed by attack of the alcohol oxygen at phosphorus to generate an oxy-phosphonium intermediate. The oxygen is then transformed into a leaving group, and an SN2 displacement by halide takes place, proceeding with inversion of configuration if the carbon is asymmetric.
Application and example :
1) Synthesis of quinine.
