Question

I was told by my teacher that RMgX forms PbR₄ when it reacts with either PbCl₂/PbCl₄ the later case is clear to me but why does PbCl₂ forms a compound of the form PbR₄.

Answer 1

Grignard reagents such as RMgX react with PbCl2 to form organometallic compounds like PbR4 by displacing the chloride ions. This shifts the equilibrium to favor the formation of PbR4 even in the presence of excess chloride from either PbCl2 or PbCl4.

Step-by-step explanation:

The reaction between RMgX (where R is an alkyl group and MgX is a Grignard reagent) and lead(II) chloride (PbCl2) to form PbR4 involves the formation of an organometallic compound. When RMgX reacts with PbCl2, the R- group acts as a nucleophile and displaces the chloride ions, thus forming PbR4. This type of reaction is characteristic of Grignard reagents which are highly reactive and can effectively exchange halide ions with organometallic groups.

This is different from the reaction with PbCl4, as the additional chloride ions (from either PbCl2 or PbCl4) would shift the equilibrium according to Le Châtelier's principle, favoring the formation of the PbR4 product. Hence, even in the case of PbCl2, the provided RMgX can drive the formation of PbR4 by effectively competing for the lead ion and overcoming the equilibrium that might otherwise favor the formation of PbCl2 with excess chloride ions.