Preparation of an aryl Grignard reagent and it’s reaction with excess trimethyl borate, forming an aryl boronic acid.
On the first picture the reddish/brown color of the solvent was caused by iodine what was added as an activator, since I used a few year old magnesium shaving for this reaction. The iodine reacts with the magnesium forming magnesium-bromide at its surface what is a bit soluble in the ether and helps the halide to react with the magnesium metal forming the Grignard reagent (ArMgX where Ar is aryl and X is a halogen, in this case bromide).
On the second picture the Grignard reagent started to form and a part of it separated from the solution. On the third picture I added a high excess of trimethyl borate what caused a vigorous reaction and a lot magnesium-bromide/methoxide separated as a white participate as seed. After this I only need to add some water, some acid to help the hydrolysis and extract the produced boronic acid from this.