Does the 'X' of Grignard's reagent react? Till whatever I have studied in organic chemistry, Grignard's reagent has been the most helpful thing everywhere, whether is it preparation or reaction of organic compounds. But I haven't ever seen the Halogen part of RMgX reacting with any compound. Does the Halogen ever react in any reaction?
Lets look at Grignard's reaction route. Key step is nucleophilic addition of R. And MgX is removed with acid on the next step. Nobody cares about X - if you want MgX2 in solution you just add MgX2. The main reason to use Grignard's reagent is nucleophilic addition of R.