A LevelChemistryEdexcelRevision Notes7. Advanced Organic Chemistry (A Level Only)7.6 Organic Chemistry III: Organic Synthesis7.6.3 Increasing Chain Length

Increasing Chain Length (Edexcel A Level Chemistry)

Revision Note

Test yourself
Philippa

Author

Philippa

Last updated

Grignard Reagents

  • If we need to increase the chain length we can use Grignard reagents 

Preparing Grignard reagents 

  • A halogenoalkane is dissolved in dry ether and reacted with magnesium to produce the reactive Grignard reagent
  • If 1-iodoethane is reacted with magnesium, ethyl magnesium iodide is produced
  • This is an example of a Grignard reagent 

CH3CH2I + Mg → CH3CH2MgI  

  • These compounds are highly reactive and the alkyl group (R group) can be considered to have a negative charge, therefore it can behave as a nucleophile 
    • R-[+MgI]

Reactions of Grignard with carbonyl compounds

  • Grignard reagents react with methanal to produce a primary alcohol 

RMgI + HCHO rightwards arrow with straight H subscript 2 straight O on top RCH2OH + Mg(OH)I

  • For example, methanal can react with ethyl magnesium iodide to produce propanol

CH3CH2MgI  + HCHO rightwards arrow with straight H subscript 2 straight O on top CH3CH2CH2OH + Mg(OH)I

  • They also can react with longer chain aldehydes to produce secondary alcohols
  • For example, ethanal can react with ethyl magnesium iodide to produce butan-2-ol

CH3CH2MgI  + CH3CHO  rightwards arrow with straight H subscript 2 straight O on top CH3CH2CH(OH)CH3 + Mg(OH)I

  • Ketones are also able to react with Grignard reagents producing a tertiary alcohol
  • For example, propanone can react with ethyl magnesium iodide to produce 2-methylbutan-2-ol 

CH3CH2MgI  + CH3COCH3 rightwards arrow with straight H subscript 2 straight O on top CH3CH2C(CH3)(OH)CH3 + Mg(OH)I

Reactions of Grignard reagents with carbon dioxide 

  • This reaction will produce a carboxylic acid

CH3CH2MgI  + CO2 begin mathsize 16px style rightwards arrow with straight H subscript 2 straight O on top end style CH3CH2COOH + Mg(OH)I

You've read 0 of your 10 free revision notes

Unlock more, it's free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

    Test yourself

    Did this page help you?

    Previous:7.6.2 Planning Reaction SchemesNext:7.6.4 Organic Techniques - Preparation
    Philippa

    Author: Philippa

    Expertise: Chemistry

    Philippa has worked as a GCSE and A level chemistry teacher and tutor for over thirteen years. She studied chemistry and sport science at Loughborough University graduating in 2007 having also completed her PGCE in science. Throughout her time as a teacher she was incharge of a boarding house for five years and coached many teams in a variety of sports. When not producing resources with the chemistry team, Philippa enjoys being active outside with her young family and is a very keen gardener.