Organic 2 Section 3 - Unit 26: Compounds containing the carbonyl groups Flashcards
Explain why ethanoyl chloride reacts readily with nucleophiles. Write an equation for one nucleophilic addition–elimination reaction of ethanoyl chloride (4 marks)
- Large charge on carbonyl carbon atom due to bonding to O and Cl
- Nucleophiles have electron pairs which can be donated
- CH3COCl (l) + CH3CH2OH → CH3CO2CH2CH3 + HCl (g)
Oxidation of aldehydes (3):
- Product
- Reagent
- Conditions
- Carboxylic Acid
- Potassium dichromate and dilute sulfuric acid
- Heat under reflux
Reduction of carbonyls (3):
- Product
- Reagent
- Conditions
- Alcohol
- NaBH4 in aqueous ethanol
- Room temperature and pressure
Addition of hydrogen cyanide to carbonyls (4):
- Mechanism
- Product
- Reagent
- Condition
- Nucleophilic addition
- Hydroxynitrile
- Sodium cyanide and dilute sulfuric acid
- Room temperature and pressure
Write an overall equation for the reduction of butanone using [H] to represent the reductant (1 mark)
- CH3CH2COCH3 + 2[H] → CH3CH2CH(OH)CH3
Give one advantage of the use of propanoyl chloride instead of propanoic acid in the laboratory preparation of methyl propanoate from methanol (1 mark)
- Faster
- Irreversible
- Bigger yield
- Purer product
- No acid catalyst required
Give one advantage of the use of propanoic anhydride instead of propanoyl chloride in the laboratory preparation of methyl propanoate from methanol (1 mark)
- Anhydride less easily hydrolysed
- Reaction less exothermic
Acyl chloride → carboxylic acid (2)
- Reagent
- Conditions
- Water
- Room Temperature
Acid Anhydride → carboxylic acid (2)
- Reagent
- Conditions
- Water
- Room Temperature
Acyl chloride → ester (2)
- Reagent
- Conditions
- Alcohol
- Room Temperature
Acid Anhydride → ester (2)
- Reagent
- Conditions
- Alcohol
- Room Temperature
Acyl chloride → primary amide (2)
- Reagent
- Conditions
- Ammonia
- Room Temperature
Acid Anhydride → Primary amide (2)
- Reagent
- Conditions
- Ammonia
- Room Temperature
Acyl chloride → secondary amide (2)
- Reagent
- Conditions
- Primary amine
- Room Temperature
Acid Anhydride → secondary amide (2)
- Reagent
- Conditions
- Primary amine
- Room Temperature
State two observations, during the determination of melting point that would indicate that a sample of aspirin is not pure (2 marks)
- Melting point range would be wide
- And below the true melting point
Give one advantage and one disadvantage of preparing ethyl ethanoate by the reaction of carboxylic acid + alcohol rather than acyl chloride and alcohol (2 marks)
Advantages:
- Reaction goes to completion, not reversible
or faster
Disadvantages:
- Reaction vigorous/dangerous or HCl is toxic
Explain why butylamine is a stronger base than ammonia (2 marks)
- Lone pair (on N) (in correct context)
- R group increases electron density / donates electrons
What sort of a reaction is Tollens’ reagent (1 mark)
- Redox reaction
Explain why ethanoyl chloride reacts readily with nucleophiles (2 marks)
- Large charge on carbonyl carbon atom due to bonding to O and Cl
- Nucleophiles have electron pairs which can be donated
Reagents for oxidation (1 mark)
Potassium dichromate
Reagents and conditions for nucleophilic addition (2 marks)
- NaBH4
- In methanol or water
Reagents and conditions for esterification (3 marks)
- Concentrated H2SO4
- Heat under reflux
- Warm
State one use of methyl esters (1 mark)
Biodiesel
Explain how you would purify a solid product by recrystallisation (4 marks)
- Dissolve the product in the minimum volume of water
- Hot water
- Allow the solution to cool and allow crystals to form
- Filter off the pure product under reduced pressure / using a Buchner funnel and side arm flask
Butanone is reduced in a two-step reaction using NaBH4 followed by dilute hydrochloric acid. Explain why the product has no effect on plane polarised light (6 marks)
Formation of product
- Nucleophilic attack
- Planar carbonyl group
- H – attacks from either side (stated or drawn)
Nature of product
- Product of step 1 shown
- This exists in two chiral forms (stated or drawn)
- Equal amounts of each enantiomer / racemic mixture formed
Optical activity
- Optical isomers / enantiomers rotate the plane of polarised light equally in
- With a racemic / equal mixture the effects cancel
Describe how you would obtain a sample of ethanal from a mixture of ethanal, ethanol and ethanoic acid (6 marks)
- Mixture heated in a suitable flask / container
- With still head containing a thermometer
- Water cooled condenser connected to the still head and suitable cooled collecting vessel
- Collect sample at the boiling point of ethanal
- Cooled collection vessel necessary to reduce evaporation of ethanal
Give one reason why ethanoyl chloride is not often used in nucleophilic addition-elimination (1 mark)
- Corrosive
- Forms strong acid / HCl fumes
