Chapter 28: Carbon-carbon Bond Formation & Practical Techniques
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In what 2 ways can nitriles be formed? What mechanisms are these reactions examples of?
• Reacting haloalkanes with sodium/ potassium cyanide • Nucleophilic substitution • Reacting aldehydes/ ketones with hydrogen cyanide • Nucleophilic addition
Write the general equation for the reaction of haloalkanes to form nitriles, and give the reaction conditions.
• Haloalkane + NaCN -> nitrile + NaX • In ethanol
Write the general equation for the reaction of aldehydes/ ketones to form nitriles, and give the reaction conditions.
• Aldehyde/ ketone + HCN -> hydroxynitrile • NaCN/ H2SO4
What can nitriles react to form, and through which processes?
• Amines through reduction • Carboxylic acids through acid hydrolysis
Write the general equation for the reaction of nitriles to form amines, and give the reaction conditions.
• Nitrile + 2H2 -> amine • Nickel catalyst
Write the general equation for the reaction of nitriles to form carboxylic acids, and give the reaction conditions.
• Nitrile + 2H2O + HCl -> carboxylic acid + NH4Cl • Heat and dilute hydrochloric acid
What are 2 other examples of reactions that increase the length of the carbon chain?
• Alkylation and acylation of benzene
What are the 3 stages of purifying an organic solid and checking its purity?
• Filtration under reduced pressure • Recrystallisation • Determining the melting point
What does filtration under reduced pressure do?
• It separates the solid from the solvent or the liquid reaction mixture
How does filtration under reduced pressure work?
• A Buchner flask is fitted with a Buchner funnel with filter paper • Pressure is created through a vacuum pump that is connected to the flask through a side arm
How does recrystallisation work?
• You choose a solvent that your solid will dissolve in when it’s hot, and the impurities will dissolve in when it’s cold • Dissolve the impure solid in the minimum possible volume of hot solvent • Cool, filter (under reduced pressure), wash with cold solvent, and leave to dry
What is the purpose of recrystallisation? Which step exactly achieves this?
• It removes impurities • The final wash with cold solvent
What can melting points determine about substances, and how? How can you tell substances are impure?
• How pure they are • Pure samples will have a sharp melting point close to the literature value • Impurities lower the melting point, and cause the substance to melt over a range of temperatures
How are melting points determined?
• Using electrically heated melting point apparatus, you find the melting point of the crystals
Why do tablets made of salts act faster in the body than tablets made of neutral molecules?
• Salts are more soluble in water