Question

How can you improve Grignard reactions?

Answer 1

There are all sorts of tips and tricks and techniques. I can give a few of mine. These all relate to starting the Grignard reaction.

Explanation:

Of course, the natural enemy of the Grignard reagent, and of organometallic reagents in general, is water. You have probably seen chemists drying glassware under vacuum with a soft bunsen flame, and performing the overall reaction under dinitrogen and argon atmospheres. Oven dried glassware is probably quite adequate. These days, we tend to be out of the flame age.

I would ALWAYS pass the halide reagent thru basic alumina before attempting to start the Grignard. Depending on the volume of the reagent, the column could simply be a Pasteur pipette filled with alumina. Alumina will dry the halide, and also take any `HCl` out. This cuts out a distillation step.

As to the metal, I would always weigh out a mass of magnesium turnings and give them a good grinding in a mortar and pestle to scratch and polish the metal surface. This often helps in starting the Grignard. It also allows you to use the expression `"freshly burnished magnesium turnings"` in your experimental.

You are probably also aware of the practice of adding an iodine chip or a few drops of ethylene bromide to start entrainment. Good luck.