Organic Chemistry: Synthesis of a Grignard Reagent

Prepare all glassware that has been oven-dried at 105°C for 24 hours to remove moisture. Pack two drying tubes with cotton wool and calcium chloride granules to prevent water from entering the system during the reaction.

Set up a three-neck flask with a clamp on the middle neck, attach a dropping funnel to one neck, a condenser with a drying tube, and position the apparatus in the fume hood with space underneath for an ice bath or heat source.

Add 2g of magnesium turnings to the flask, then gradually add a mixture of 12.9g bromobenzene in 40ml sodium-dried ether. Warm gently with hands or a 40°C water bath, and crush magnesium turnings if needed to initiate the reaction.

Keep the ether boiling under reflux for approximately 15 minutes, monitoring the condenser level to prevent ether loss. Observe the solution change from clear to dark brown, indicating oxidation product formation and successful Grignard reagent synthesis.

Slowly add 8ml of benzaldehyde in ether through the dropping funnel to the reaction mixture, observing white alkoxide ion precipitation. Heat the reaction mixture with warm water for approximately 30 minutes to allow the reaction to proceed.

Cool the solution in an ice bath, then slowly add cold sulfuric acid over 20 minutes while swirling continuously. The alkoxide protonates to form dimethyl alcohol product, and any remaining magnesium reacts with the acid to produce hydrogen gas bubbles.

Transfer the two-layer mixture (sulfuric acid bottom, ether with product on top) to a separating funnel. Wash the ether layer multiple times, dry with magnesium sulfate, and evaporate the solvent to obtain the final white solid product.