These questions is based on Grignard Synthesis of Malachite Green A) You are dir

Question

These questions is based on Grignard Synthesis of Malachite Green A) You are directed to polish the magnesium turnings. What's the purpose of doing this? Specifically, what is removed by polishing? B) Why are we being so careful to eliminate moisture from the reaction vessel, solvent, etc? What is the reaction that will occur if water is present? C) If the Grignard reagent doesn't seem to be forming, you are directed to grind the mixture a bit using a flat-headed stir rod. Why/how might this get the reaction started?

Explanation / Answer

A) The Magnesium metal initially has a layer of oxide on the surface; polishing under an absolutely dry solvent in the presence of an organic halide will expose a fresh unoxidised surface. B) The Grignard reagent is a strong base and a strong nucleophile. As a base it will react with all protons that are more acidic than those found on alkenes and alkanes. Thus, Grignard reagents react readily with water, alcohols, amines, thiols, etc., so the reactants and apparatus must all be completely dry and free of acidic protons, otherwise the reaction will not start. C) Crushing exposes a larger surface region of the reactants thus providing greater number of regions where the reaction can start, thus making the reaction possible.

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