Question

This is a lab question for the synthesis of triphenylmethanol using a Grignard reaction. "After the Grignard reaction is over, and before you added HCl, you notice some unreacted Mg turnings. What implications will this have on your yield of triphenylmethanol? Is it possible to get a 100% yield if not all the Mg has reacted?"

Answer 1

If the quantity of the Magnesium (Mg) used in the reaction is only one equivalent with respect to the starting material then if any unreacted Mg turnings observed after the reaction, the yield of the product will not be 100% as sufficient Grignard reagent is not available for the complete conversion of the starting material into the product.

However, if one uses excess equivalents (more than one) of Mg in the reaction, in this case even some unreacted Mg turnings doesn't affect the yield of the product.