Appel Reaction
The Appel reaction allows the conversion of an alcohol into the corresponding alkyl chloride under mild conditions by the reaction of triphenylphosphine and tetrachloromethane with the alcohol.
General features:
1. The use of toxic halogenating agents and the coproduction of organophosphorus products that must be separated from the desired product triggered the investigations of greener and more sustainable catalytic Appel reactions, free from chlorinated solvents. 2. The phosphorus reagent can be used in catalytic quantities.
Appel Reaction
Reaction Mechanism
1. Activation of triphenylphosphine by reaction with tetrachloromethane generates the phosphonium salt. 2. Deprotonation of the alcohol yields chloroform and an alkoxide derivative. 3. The alkoxide attacks the phosphonium salt at the phosphorus centre to generate an oxyphosphonium intermediate, making the oxygen a good leaving group. 4. Displacement by the halide generates the alkyl halide and triphenylphosphine oxide.
Example
Experimental Procedure
To a cooled solution (0 ºC) of the alcohol (4.60 mmol, 1.0 eq.) in anhydrous CH2Cl2 (50 mL) were added CBr4 (1.3 eq.) and PPh3 (1.5 eq.) under a nitrogen atmosphere. The resulting mixture was stirred at 0 ºC for 30 min and then concentrated under reduced pressure. The residue was purified by flash column chromatography on silica gel to give the alkyl bromide (95% yield).
Learn More Named Reactions
