Question

1) An unavoidable side reaction of alkyl halides with active metals which lowers the yield of Grignard reagents is called coupling.

2RX + Mg ------> R-R + MgX2

Although the mechanism of the coupling process is not well understood, it is known that the rate appears to depend on the square of the concentration of the halide. With this in mind, explain the reason for the sequence of addition of the ether solution employed at the beginning of the formation of the Grignard reagent in the experimental procedure above.

Answer 1

In presence of dry ether, metal reacts with only alkyl halide rather than any other compounds in reaction mixture, generally water contaminent is there ,the metal reacts with water to form metal hydroxide with explosive nature.

if reaction contains water like polar solvent it favours the formation of carbocation and those are stabilized by water.so to avoid all these reactions we have to use dry ether.