Organic synthesis and reaction pathwaysEdexcel A-Level Chemistry: Subtopic test

1. 1
   An organic liquid X contains only carbon, hydrogen and oxygen. Complete combustion of 0.296 g of X gives 0.704 g of carbon dioxide and 0.360 g of water. The mass spectrum of X has its molecular ion peak at m/z = 74. The infrared spectrum of X has a broad absorption at about 3300 cm⁻¹ and no absorption near 1700 cm⁻¹. Relative atomic masses: H = 1.0, C = 12.0, O = 16.0.

   (a)

   What is the empirical formula of X?

   [1 mark]

   • AC₄H₁₀O
   • BC₂H₅O
   • CC₄H₈O
   • DC₃H₈O

   (b)

   What does the infrared spectrum show about X?

   [1 mark]

   • AIt contains a C=O group of an aldehyde or ketone
   • BIt contains the C=O and O–H groups of a carboxylic acid
   • CIt contains an O–H group of an alcohol and no C=O group
   • DIt contains an N–H bond of an amine

   (c)

   The ¹H NMR spectrum of X has two singlets with relative peak areas 9 : 1, and X is not oxidised by warm acidified potassium dichromate(VI). Deduce the structural formula of X and explain how the data support your answer.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Grignard reagents are made by reacting a bromoalkane with magnesium. Ethylmagnesium bromide, CH₃CH₂MgBr, is made from bromoethane and is then used to lengthen carbon chains.

   (a)

   Which conditions are used to make CH₃CH₂MgBr from bromoethane?

   [1 mark]

   • AMagnesium in aqueous ethanol, warmed
   • BMagnesium turnings in dry ether, with no water present
   • CMagnesium and dilute hydrochloric acid
   • DMagnesium in aqueous sodium hydroxide

   (b)

   CH₃CH₂MgBr is reacted with solid carbon dioxide and the mixture is then treated with dilute acid. What is the organic product?

   [1 mark]

   • APropan-1-ol
   • BPropanal
   • CButanoic acid
   • DPropanoic acid

   (c)

   CH₃CH₂MgBr reacts with propanone, and dilute acid is then added. Give the structural formula of the organic product and explain why the Grignard reagent attacks the carbonyl carbon.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Chemists often need to lengthen a carbon chain by one carbon atom. Butanoic acid can be made from propan-1-ol by a route using a nitrile or by a route using a Grignard reagent. Hazard data: potassium cyanide is toxic if swallowed or in contact with skin and releases toxic hydrogen cyanide gas with acids; diethyl ether is extremely flammable (flash point −45 °C) and can form explosive peroxides; Grignard reagents react violently with water.

   (a)

   Suggest a three-step route from propan-1-ol to butanoic acid using a nitrile. Give the reagents and conditions for each step.

   [3 marks]

   (b)

   Using the hazard data, describe one control measure for each of the nitrile route and the Grignard route, and justify which route you would choose for a school laboratory.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Aspirin (2-ethanoyloxybenzoic acid, Mᵣ = 180.0) is made in school laboratories from 2-hydroxybenzoic acid (salicylic acid, Mᵣ = 138.0) and an excess of ethanoic anhydride, with concentrated phosphoric(V) acid as a catalyst. In one preparation 2.76 g of salicylic acid was used and 2.52 g of pure, dry, recrystallised aspirin was obtained.

   (a)

   Describe how a pure, dry sample of aspirin is prepared from salicylic acid and ethanoic anhydride, including how the crude product is purified and how its purity is checked.

   [6 marks]

   (b)

   Calculate the percentage yield of aspirin in this preparation. Suggest two reasons why the yield is less than 100%, and explain how measuring the melting temperature of the product shows whether it is pure.

   [6 marks]

   Total for question 4: 12 marks

End of questions