Question

Why must a Grignard reaction be dry?

Answer 1

Because water is the natural enemy of the Grignard reagent. See this old answer.

Explanation:

You will see chemists flame dry their glassware with a soft bunsen flame prior to an organometallic reaction (a heady mix with ethereal solvents about to be used!). As explained in the link, sometimes, the water sensitivity of Grignards can be exploited.

Answer 2

1. GRIGNARD REACTION IS CARRIED OUT IN DRY ETHER
2. AS IF NOT
   R negative will react with solvent and the product which we need is not obtained effectively