RX RMgX
ArX ArMgX
+ Mg Et^2 O
+ Mg Et^2 O
Grignard reagents
1) The order of reactivity of halides with magnesium is RI > RBr > RCl (very few
organomagnesium fluorides have been prepared).
i) Aryl Grignard reagents are more easily prepared from aryl bromides and aryl
iodides than from aryl chlorides, which react very sluggishly.
- Grignard reagents are seldom isolated but are used for further reactions in ether
solution.
- Mg 35 oC Methylmagnesium iodide
Et 2 O
(95%)
CH 3 X CH 3 MgX
+ Mg 35 oC Phenylmagnesium bromide
Et 2 O
(95%)
C 6 H 5 X C 6 H 5 MgX
- The actual structures of Grignard reagents are more complex than the general
formula RMgX indicates.
- Experiments done with radioactive magnesium have established that, for most
Grignard reagents, there is an equilibrium between an alkylmagnesium halide
and a dialkylmagnesium.
2 RMgX R 2 Mg + MgX 2
Alkylmagnesium halide Dialkylmagnesium
- For convenience, RMgX is used for the Grignard reagent.
- A Grignard reagent forms a complex with its ether solvent:
