Titrate a known mass of iodine (I₂) with anhydrous tetrahydrofuran (THF) against your Grignard reagent until the brown/red colour disappears and the solution becomes cloudy/colourless. 1:1 stoichiometry (RMgX + I₂ → RI + MgXI) gives the active concentration directly.
To a round-bottom flask was added 200 mg of I₂ and THF (2.00 mL), under an argon atmosphere. Then, the Grignard reagent was added dropwise until the expected colour change was observed. LiCl can be added to the THF solution (0.5 M) prior to addition of I₂, to enable clearer endpoint determination.
Bench Beta v1.0