Tertiary phosphine oxides are also obtained by the Michaelis-Arbuzov reaction, which involves the reaction of phosphine acid esters with alkyl halides to give intermediate phosphonium salts, followed by rapid decomposition.
Most common is the preparation of alkyl phosphonic acid esters from phosphorous acid esters. The preparation of phosphonic acid esters from phosphonous acid esters as well as phosphine oxides from phosphinous acid esters is also possible.
MechanismBack to Top
One typical example of Arbuzov reaction heating triethyl phosphite with a small amount of ethyl iodide to give diethyl ethylphosphonate in high yield.
The first step is the addition of the alkyl halide to the phoshite to give a phosphonium salt.
This intermediate product is unstable under the reaction conditions, and reacts by cleavage of an O-alkyl bond to yield the alkyl halide and the alkyl phophonate.
The following three facts are experimentally established.
- The concentration of ethyl iodide is maintained constant throughout the reaction.
- The reaction rate is proportional to the concentration of ethyl iodide.
- The reaction is faster in solvents with larger dipole moment than in non-polar solvent.