Briefing video - Grignard

Learn the key concepts of the Grignard experiment: preparing an unstable Grignard reagent from bromobutane and magnesium, then using it to react with a ketone. Understand why the reagent must be prepared in advance and kept away from air and moisture.

Identify the key techniques you will perform: controlled addition of ketone to the Grignard reagent, liquid-liquid extraction for workup, and reduced-pressure distillation of the final product. Familiarize yourself with the specialized glassware setups shown in accompanying videos.

Ensure all glassware is completely dry using an oven or hair dryer, as Grignards react with water and moisture will lower your yield. Add bromobutane to magnesium and watch for bubbling to confirm Grignard reagent formation; consult a demonstrator if no bubbling occurs.

Slowly add your ketone to the formed Grignard reagent while monitoring the reaction. Maintain control by using an ice bath to cool the reaction if it becomes too vigorous, and apply gentle warming as needed to continue the reaction and Grignard formation.

After the reaction is complete, perform standard workup using a separatory funnel and then use a rotary evaporator to concentrate your crude product. This step typically takes 1-2 hours.

Attach a vacuum pump line to your distillation apparatus to lower the pressure below 30 millimeters of mercury. This allows safe distillation of the high-boiling-point product at lower temperatures to prevent degradation. Only one person per fume hood can use the vacuum at a time.

Perform reduced-pressure distillation, using a pig adapter to connect three flasks. Unreacted ketone will distill first into the first flask at a lower temperature; when temperature rises, rotate the adapter to switch flasks and collect the product in a fresh flask. This distillation step takes 2-3 hours.