What is the limiting reactant in a Grignard reaction?

Question

Mateo Aguilar · Accepted Answer

The limiting reagent in a Grignard reaction is usually the substance to which you add the Grignard reagent, but you have to confirm this by calculation.

AN EXAMPLE Assume that 2.1 mL of bromobenzene (density 1.50 g/mL) and 0.50 g of magnesium in anhydrous ether were reacted to create phenylmagnesium bromide in a triphenylmethanol preparation. To this, you then gradually added a solution of 2.4 g benzophenone in anhydrous ether. What was the limiting reactant in this reaction? Resolution The equations (#"Ph" = "C"_6"H"_5#) are: #"PhBr" + "Mg" → "PhMgBr"# #"Ph"_2"C=O" + "PhMgBr" → "Ph"_3"COMgBr"# #"Ph"_3"COMgBr" + "H"^+ → "Ph"_3"COH" + "Mg"^(2+) + "Br"^"-"# Determine each reactant's moles. #2.1 color(red)(cancel(color(black)("mL PhBr"))) × (1.50 color(red)(cancel(color(black)("g PhBr"))))/(1 color(red)(cancel(color(black)("mL PhBr")))) × "1 mol PhBr"/(157.0 color(red)(cancel(color(black)("g PhBr")))) = "0.020 mol PhBr"# #0.50 color(red)(cancel(color(black)("g Mg"))) × "1 mol Mg"/(24.30 color(red)(cancel(color(black)("g Mg")))) = "0.021 mol Mg"# #2.4 color(red)(cancel(color(black)("g Ph"_2"CO"))) × ("1 mol Ph"_2"CO")/(182.2 color(red)(cancel(color(black)("g Ph"_2"CO")))) = "0.013 mol Ph"_2"CO"# Determine which reactant is limiting. The molar ratios in theory are all 1:1. Benzophenone is the limiting reactant because it has the fewest moles.

Caleb Adams · Answer

undefined The limiting reactant in a Grignard reaction is the reactant that is completely consumed first and determines the maximum amount of product that can be formed.