Michaelis-Arbuzov reaction

The Michaelis-Arbuzov reaction is the chemical reaction of a trialkyl phosphite and an alkyl halide to form a phosphonate.

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The reaction was discovered by Michaelis in 1898^[1], and greatly explored by Aleksandr Arbuzov soon thereafter.^[2][3] This reaction is widely used for the synthesis of various phosphonates, phosphinates, and phosphine oxides. Several reviews have been published.^[4][5]

Reaction mechanism

The Michaelis-Arbuzov reaction is initiated with the S_N2 reaction of the nucleophilic phosphite (1) with the electrophilic alkyl halide (2) to give a phosphonium intermediate (3). Triaryl phosphites, which are unable to perform the second step of the Michaelis-Arbuzov reaction, have been shown to produce stable phosphonium salts.^[6] Likewise, aryl and vinyl halides are unreactive towards phosphites.

The displaced halide anion reacts via another S_N2 reaction with the phosphonium intermediate to give the desired phosphonate (4) and another alkyl halide (5). When chiral phosphonium intermediates are produces, it has been shown the halide substitution proceeds with inversion of configuration, as expected by a S_N2 reaction.^[7]

As a general guideline, the reactivity of the organic halide (2) can be listed as follows: (from most reactive to least reactive)

RCOX > RCH2X > RR'CHX >> RR'R"CX

and

RI > RBr > RCl

The Michaelis-Arbuzov reaction of α-bromo- and α-chloroketones does not give the expected product. This side reaction is called the Perkow reaction. α-Iodoketones do, in fact, give the expected phosphonate.^[8] Other methods of producing β-ketophosphonates have been developed.^[9]

References

See also

• Perkow reaction