Edexcel Jun 2014 (R) Paper 5 Q22

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22 Paracetamol is a mild painkiller which also reduces the temperature of patients with fever, actions known as analgesic and antipyretic respectively. The reaction scheme below summarises a laboratory synthesis of paracetamol starting from phenol. The yields shown are for the particular product of each step in the synthesis. OH OH 50% H2SO4 NaNO3(s) NO2 OH 25% yield OH NaBH4 NaOH(aq) NH2 74% yield paracetamol HN 85% yield OH NO2 (a) The nitration of benzene is an electrophilic substitution reaction that requires concentrated nitric and sulfuric acids. (i) Write an equation for the formation of the electrophile by the reaction between concentrated nitric and concentrated sulfuric acids. (2) 18 *P42989rA01828*<br /> (ii) Give the mechanism for the formation of nitrobenzene from benzene. (iii) Explain why phenol is nitrated in much milder conditions than benzene. (3) (2)(iv) Suggest why the yield for the nitration of phenol is so low. (1)(v) Suggest an alternative to NaBH4 that could be used in aqueous solution. (1)(vi) Calculate the overall yield of the synthesis. (1) *P42989rA01928* 19 Turn over<br /> (b) The paracetamol, prepared by the synthesis shown at the start of the question, may be purified by recrystallization. In this process, the paracetamol is dissolved in a minimum volume of hot water, the hot mixture filtered, the filtrate cooled and the resulting crystals filtered and dried. The table below summarises the solubility of paracetamol in water at various temperatures. Temperature / (cid:113)C Solubility / g / 100 g 0.82 10 0.94 20 1.3 95 5.2 (i) Explain the purpose of each of the filtrations in the recrystallization of paracetamol. (2)(ii) From the temperatures given in the table, choose the pair of temperatures that will give the highest yield of paracetamol from the recrystallization. Explain your choice. (2)(iii) Name the technique that could be used in a school laboratory to check the purity of the recrystallized paracetamol. (1)20 *P42989rA02028*<br /> (c) The mass spectrum of paracetamol is shown below. Relative intensity 100 80 60 40 20 10 25 50 75 100 125 150 m/e (i) Label the molecular ion peak, with an M, on the mass spectrum. (ii) Suggest the formula of an ion that could cause the peak at m/e = 43. (d) Paracetamol is highly toxic: overdosing causes irreversible liver damage. Despite this, paracetamol is readily available from pharmacies and even supermarkets. Suggest one control measure that sellers might employ to reduce the risk to paracetamol users. (1) (1) (1)(Total for Question 22 = 18 marks) TOTAL FOR SECTION B = 50 MARKS *P42989rA02128* 21 Turn over<br />

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