Grignard Reaction Process

Overview

• Grignard reaction is used to form new carbon-carbon bonds.
• Sensitivity to water is a major downside; even small amounts can ruin the reaction.

Chemicals Used

• Magnesium
• Dry Ether
• Bromopropane
• Hydrochloric Acid (HCl)
• Sodium Hydroxide (NaOH)

Equipment and Setup

• Three-necked round bottom flask, oven-dried.
• Magnesium (1.5g) and dry ether (15 ml) added to the flask.
• Apparatus closed to the atmosphere with a drying tube on the condenser column.

Reaction Steps

Initiation

• 5 ml of bromopropane injected into the solution.
• Slowly add bromopropane until the reaction starts (ether starts to reflux and boil).
• If the reaction doesn’t start, add iodine crystals.

Reaction Monitoring

• Solution turns black as the reaction progresses.
• Ether volume maintained by constant addition due to loss through reflux.
• Use a cold condenser to reduce ether loss.
• Reaction between bromopropane and magnesium forms the Grignard reagent, which is exothermic, causing ether to boil.

Completion

• Bubbling and ether boiling stop when the reaction is complete.
• Allow solution to cool to room temperature.

CO2 Reaction

• CO2 generator set up using dry ice.
• Flask flushed with nitrogen to avoid moisture.
• CO2 fed into the solution with stirring, making the solution thicker.
• Maintain ether volume due to loss during CO2 bubbling.
• Bubble CO2 for at least 15 minutes.

Hydrolysis and Product Formation

• Transfer product to an Erlenmeyer flask and wash with 60 ml of 3M HCl.
• Hydrochloric acid addition induces hydrolysis, forming final butyric acid.
• Solution should be transparent with a small ether layer on top and aqueous layer at the bottom.

Filtration and Washing

• Vacuum filter the solution into a separatory funnel.
• Remove unreacted magnesium.
• Wash apparatus with 50 ml of ether.

Separation Steps

• Drain and discard the aqueous layer.
• Wash ether layer with:
  • 30 ml of water
  • 21 ml of 3M NaOH (twice, saving aqueous layers each time)
  • 15 ml of water
• Re-acidify aqueous layers with 50 ml of 3M HCl to regenerate butyric acid.

Final Extraction

• Extract the acid with 30 ml of ether, thrice.
• Wash combined ether layers twice with 50 ml saturated salt solution.
• Dry ether washings with sodium sulfate.

Evaporation and Final Product

• Evaporate ether using a separatory funnel and small vial.
• Final product appears pink, possibly contaminated.
• NMR run shows clean butyric acid despite color.

Notes

• Ether loss is substantial; maintain careful volume.
• Use multiple washings for better extraction efficiency.
• Final product's pink color remains unidentified, yet purity confirmed by NMR.