Lecture on Grignard Reaction

Introduction to Grignard Reaction

• Purpose: Useful for forming new carbon-carbon bonds.
• Major Downside: Highly sensitive to water; even small amounts can ruin the reaction.

Materials Used

• Magnesium: 1.5g
• Dry Ether: Quantity unspecified as it should be abundant.
• Bromopropane: 5 ml
• Hydrochloric Acid & Sodium Hydroxide: Quantities not listed as they should be abundant.
• Oven-dried equipment: 3-necked round bottom flask.

Reaction Setup

1. Equipment Setup:

   • Use a 3-necked round bottom flask charged with magnesium and dry ether.
   • Apparatus closed from atmosphere; drying tube at condenser column.

2. Initiating Reaction:

   • Inject bromopropane slowly till reaction starts, then add the rest.
   • Ether starts to reflux and boil.
   • If reaction doesn’t start, add iodine crystals.
   • Maintain constant ether volume by continuous addition.

3. Reaction Process:

   • Exothermic reaction between bromopropane and magnesium forms the Grignard reagent.
   • Important for ether to boil; condenser column needed to control ether loss.

Post-Reaction Process

• Cooling: Once bubbling stops, allow solution to cool.
• CO2 Introduction: Use dry ice to set up a CO2 generator.
• Sensitivity: Reagent is sensitive to moisture, hence flush flask with nitrogen.

Concluding Reaction

• Bubbling CO2: Through solution for 15 minutes; solution thickens.
• Hydrochloric Acid Addition: Washed with 3 molar hydrochloric acid to induce hydrolysis.

Separation and Purification

1. Vacuum Filtration:

   • Filter the solution to remove unreacted magnesium.
   • Wash with ether, separate aqueous and ether layers.

2. Washing Process:

   • Ether layer washed with water, sodium hydroxide, and saved.
   • Re-acidify aqueous layers using hydrochloric acid.

3. Extraction:

   • Use ether to extract butyric acid multiple times for better yield.
   • Dry combined ether layers with saturated salt solution and sodium sulfate.

Final Product

• Product Description: Final product is butyric acid.
• Contamination: Pink color indicates contamination, but NMR results are clean.

Summary

• The Grignard reaction is a meticulous process requiring precise management of materials and conditions.
• Critical reaction points: initiation, maintaining reaction conditions, and layered product separation.
• Importance of multiple washing and extraction steps to maximize yield and purity.