Question

Grignard reagent is usually prepared by
`R-X+Mg overset(Et_(2)O)rarrRMgX " " "Grignard reagent"`
`Ar-X+Mg overset(Et_(2)O)rarrArMgX " " "Grignard reagent"`
Grignard reagent acts s a strong base. Grignard reagent carry out nucleoplilic attack in absence of acidic hydrogen. Grignard reagent form complex with its ether solvent. Complex formation with molecule of ether is an important factor in the formation and stability of Grignard reagent.
What is the correct order of reactivity of halides with magnesium ?
A. `R-Cl gt R-Br gt R-I`
B. `R-Br-gt R-Cl gt R-I`
C. `R-I gt R-Br gt R-Cl`
D. `R-I=R-Br=R-Cl`

Answer 1

Correct Answer - C
Grignard reagents are usually prepared by the reaction by the reaction of an organic halide and magnesium metal (turnings) in an ether solvent.
`{:(RX+Mg overset(Et_(2)O)rarrRMgX),(ArX+Mg overset(Et_(2)O)rarrArMgX):}} "Grignard reagents"`
The order of reactivity of halides with magnesium is also `RI gt RBr gt RCl`. Very few organomagnesium fluorides have been prepared. 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. The ether solution can be analyzed for the content of the Grignard reagent, however, and the yields of Grignard reagents are almost always very high (85-95%). Two examples are shown here:
`CH_(3)I+Mg underset(35^(@)C)overset(Et_(2)O)rarr underset((95%))underset("Methylmagnesium iodide")(CH_(3)MgI)`
`C_(6)H_(5)Br+Mgunderset(35^(@)C)overset(Et_(2)O)rarr underset((95%))underset("Phenylmagnesium bromide")(C_(6)H_(5)MgBr)`