13622.06R [Turn over 14 Aspirin, C9H8O4, may be synthesised in the laboratory using the reaction of salicylic acid with excess ethanoic anhydride. The equation for the reaction is given below. salicylic acid C O OH OH ethanoic anhydride C O C O H3C H3C O aspirin C O O OH ethanoic acid C O CH3 C O HO H3C (a) State the IUPAC name for salicylic acid. [1] (b) State the IUPAC name and draw the structural formula of another compound which will react with salicylic acid to form aspirin. Explain why ethanoic anhydride is used in preference to this compound. [3] (c) Identify the ion which causes the peak at an m/z ratio of 43 in the mass spectrum of ethanoic anhydride. [1] 13622.06R (d) State the approximate chemical shifts, peak integration and any splitting patterns observed in the 1H nmr spectrum of ethanoic acid. chemical shift: peak integration: splitting pattern: [3] (e) Both the - COOH group and the - OH group in salicylic acid can ionise in solution. (i) Write an equation for the ionisation of salicylic acid in which both of these groups are ionised. [1] 13622.06R [Turn over (ii) The synthesis of aspirin may be monitored using iron(III) chloride solution. The iron(III) ion forms a purple complex with the completely ionised salicylic acid. This complex is shown below. O O C O OH2 OH2 OH2 OH2 Fe Write an ionic equation for the formation of the complex from an aqueous solution of iron(III) ions and the ionised salicylic acid. [1] (iii) State the co-ordination number and shape of the complex in (e)(ii). co-ordination number shape [2] 13622.06R (f) Thin-layer chromatography (TLC) may also be used to monitor the progress of the synthesis of aspirin in the laboratory. The solvent used is ethyl ethanoate. The chromatogram is dried thoroughly and developed using an alkaline solution of potassium manganate(VII) which stains the TLC plate purple. After strong heating of the TLC plate, most organic compounds show as a yellow/brown spot due to the presence of a mixture of green manganate(VI) ions, MnO2 4 -, and black manganese(IV) oxide. The Rf values for the reactants and products are shown below. Rf salicylic acid aspirin ethanoic anhydride ethanoic acid 0.315 0.800 0.545 0.380 (i) Write a half-equation for the conversion of manganate(VII) to manganate(VI). [1] (ii) Suggest the type of reaction which organic compounds undergo in the presence of alkaline potassium manganate(VII). [1] 13622.06R [Turn over (iii) Describe, giving experimental details, how TLC can be carried out on a sample of the reaction mixture and the Rf values calculated and used to determine if the reaction is complete. In this question you will be assessed on your written communication skills including the use of specialist scientific terms. [6] 13622.06R (g) 4.50 g of a sample of impure solid aspirin were mixed with an excess of sodium hydroxide in solution (40.0 cm3 of 1.25 mol dm-3). The mixture was heated and diluted to 250.0 cm3 using deionised water in a volumetric flask. A 25.0 cm3 sample of the solution was titrated against 0.140 mol dm-3 hydrochloric acid using phenolphthalein indicator. 14.3 cm3 of hydrochloric acid were required. Aspirin reacts with sodium hydroxide according to the equation: C9H8O4  +  2NaOH  →  C7H5O3Na  +  CH3COONa  +  H2O (i) State the colour change observed at the end point of the titration. [1] (ii) Name the two types of reaction occurring when sodium hydroxide reacts with aspirin. [2] (iii) Calculate the mass of aspirin in the sample. Give your answer to 3 significant figures. Answer g [5] 13622.06R [Turn over (iv) The manufacturer’s given value for the percentage of aspirin in the sample was 65%. Calculate the percentage of aspirin in the sample from the titration. Answer % [1] (v) Suggest why the value calculated in (g)(iv) may be different to the manufacturer’s given value. [1] (h) Aspirin is metabolised in the liver to form gentisic acid which is excreted by the kidneys in urine as it is more soluble in water than aspirin. gentisic acid C O HO OH OH (i) Suggest the IUPAC name of gentisic acid. [1] (ii) Explain why gentisic acid is more soluble in water than aspirin. [2]