Lecture on Grignard Reactions

Introduction to Grignard Reactions

• Grignard Reagent Formation
  • React methyl bromide with magnesium
  • Magnesium inserts between carbon and bromine
  • Forms methyl magnesium bromide
  • Requires ether solvent (not water or alcohol)

Mechanism of Grignard Reactions

• Magnesium's Role

  • Magnesium in the second column of the periodic table
  • Has 2 valence electrons, very reactive
  • Loses electrons to carbon, forming carbon anion
  • Bromine more electronegative, pulls electrons

• Resulting Ionic Charges

  • Carbon with negative charge, unstable
  • Bonds with magnesium ion
  • Forms ethyl magnesium bromide

Reaction Properties

• Grignard Reagent and Water

  • Reacts with water, forms methane
  • Carbon grabs hydrogen, expels hydroxide

• Isotope Reaction Example

  • D2O reaction replaces hydrogen with deuterium

Applications of Grignard Reagents

• Alkylation

  • Butyl magnesium bromide reacts with another alkyl halide
  • Carbon bonds form, increasing chain length

• Alcohol Formation

  • Primary alcohol: Grignard with formaldehyde
  • Secondary alcohol: Grignard with aldehyde with R group
  • Tertiary alcohol: Grignard with ketone

Carboxylic Acid Synthesis

• Using Grignard Reagents
  • Reacts with CO2 to form carboxylic acids

Epoxide Reactions

• Making Alcohols
  • Grignard reagent can react with epoxides
  • Various alcohol types can be synthesized by modifying epoxide structure

Acid Chloride and Ester Reactions

• Multiple Additions
  • Grignard can add 2 R groups to acid chloride or ester
  • Formation of tertiary alcohols

Synthesis Problems

• Identifying Reagents
  • Use Grignard to add specific R groups
  • Synthesis examples with secondary and tertiary alcohols

Converting Alcohols

• To Alkyl Chlorides
  • Use SO2 or PBr3 for conversion
  • SN2 reaction mechanism for primary and secondary alcohols

Advanced Synthesis Examples

• Cy and Trans Alkene Formation
  • Grignard with alkynes
  • Use hydrogen gas/lindlar catalyst or sodium in liquid ammonia

Ring-Closing Reactions

• Ring Formation
  • When Grignard reagent and reactive group are in the same molecule
  • Forms cyclic structures

Conclusion

• Overall Summary
  • Grignard reactions are versatile for forming carbon-carbon bonds
  • Useful for synthesizing various organic compounds
• Potential for Further Study
  • Explore additional reactions and mechanisms