Grignard Reactions and Tertiary Alcohols Preparation

Safety Precautions

• Alkyl halides are carcinogenic.
• Magnesium is a reactive flammable metal.
• Diethyl ether is volatile and highly flammable.
• Wear gloves and work in a fume hood.
• Implement fire safety protocols.

Introduction to Grignard Reactions

• Carbon-Carbon Bond Formation: Essential in organic chemistry for creating longer carbon chains.
• Grignard Reaction: A classic method to form carbon-carbon bonds using alkyl magnesium halides.
  • Reacts with carbonyl compounds to produce longer chain alcohols.
  • Other applications: formation of amines, peroxides, carbonyls, and coupling reactions.
• Focus: Making tertiary alcohols for further research on alkali metals.

Experiment Overview

• Tertiary Alcohols: 2-methyl-2-octanol, t-amyl alcohol, 3-ethyl-3-pentanol, and 7-hexyl-7-tridecanol.
• Techniques used: sodium drying, steam distillation, Dean-Stark drying.

Purification of Solvents

• Grignard reactions are sensitive to water and impurities.
• Purified Diethyl Ether: Must be free from impurities like alcohols and acids.
  • Process: React ether with potassium hydroxide and sodium metal, then distill.

Preparation of Grignard Reagent

• Materials: 12g magnesium turnings, 200mL purified diethyl ether.
• Activation of Magnesium:
  • Inject 2g bromohexane, stir, wait for clouding/bubbling indicating reaction.
  • Drip in bromohexane and ether mixture slowly to avoid thermal runaway.
• Formation of Grignard Reagent: Magnesium reacts with bromohexane to form hexylmagnesium bromide.

Grignard Reaction with Carbonyl Compound

• Target Compound: 2-methyl-2-octanol.
  • React hexylmagnesium bromide with acetone.
  • Products precipitate; stir to maintain suspension.
• Aqueous Workup:
  • Add reaction mixture to cold water.
  • Titrate with hydrochloric acid to dissolve magnesium hydroxy bromide.
  • Separate layers using a separatory funnel.
  • Distill off diethyl ether and purify to obtain alcohol.

Preparation of Tertiary Amyl Alcohol

• Reagents: 20g magnesium, diethyl ether, 80g bromoethane.
• Procedure similar to previous reaction.
• Target Alcohol: t-amyl alcohol.

Use of Esters for Larger Alcohols

• Ethyl Propionate: Reacts to form 3-ethyl-3-pentanol.
• Difference from ketones: Multiple steps form larger alcohols.

Organic Carbonates for Very Large Alcohols

• Produces esters, then ketones, and finally alcohols.
• Propylene Carbonate: Used to produce 7-hexyl-7-tridecanol.

Final Purification Techniques

• Steam Distillation: Used for high boiling point alcohols.
• Dean-Stark Apparatus: Removes water through azeotropic distillation.

Challenges and Results

• Achieved various tertiary alcohols with amateur conditions.
• Grignard reactions can be high yielding with pure lab-grade chemicals.

Future Experiments

• Aim to make alkali metals like potassium and sodium.

Acknowledgments

• Thanks to supporters on Patreon for funding.

Conclusion

• The Grignard reaction remains a versatile and valuable tool in organic synthesis, especially useful for creating complex tertiary alcohols.