Edexcel Jun 2016 Paper 5 Q23 (with explained solutions) |

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Edexcel Jun 2016 Paper 5 Q23

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SECTION C Answer ALL the questions. Write your answers in the spaces provided. 23 Analgesics Analgesics are taken to relieve the symptoms of pain. Paracetamol This has been synthesised in a three-step process since the 1950s. HO Ibuprofen This was first synthesised in the 1960s from propanoic acid. That process involved six steps and produced more waste than the required drug. OH It is now manufactured in a three-step process. Some data about these two analgesics are given in the table below. Analgesic paracetamol ibuprofen Molecular formula Molar mass / g mol1 C8H9NO2 C13H18O2 151 206 A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D *P46661A02532* 25 Turn over<br />
(a) Name the functional group in paracetamol, other than the phenol group. (1)(b) Paracetamol is made from phenol in a three-step process. D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A dilute H2SO4 NaNO3 Step 1 HO NO2 4-nitrophenol NH2 NO2 NaBH4 Step 2 HO Step 3 HO HO NO2 2-nitrophenol (i) In a typical nitration of an arene, the electrophile is formed as shown below. HNO3 + H2SO4 (cid:108) H 2NO3 + + HSO4Equation 1HO HO H2NO3 + (cid:108) H2O + NO2 + Equation 2 Identify the acid-base conjugate pairs in Equation 1. Write your answers on the dotted lines under the equation. (1) D O N O T W R I T E I N T H I S A R E A 26 *P46661A02632*<br />
(ii) Give a mechanism for the nitration of phenol by NO2 + to form 4-nitrophenol. (iii) Explain why phenol is nitrated much more readily than benzene. (3) (2)(iv) State the type of reaction taking place in Step 2. (1)(v) Suggest a reagent for Step 3. (1)A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D *P46661A02732* 27 Turn over<br />
(vi) 2-nitrophenol has a melting temperature of 46 oC and 4-nitrophenol has a melting temperature of 114 oC. Suggest, in terms of intermolecular forces, why these two compounds have different melting temperatures. (2)(c) Paracetamol can be hydrolysed to form 4-aminophenol and ethanoic acid. + H2O NH2 CH3COOH HO HO The amount of 4-aminophenol produced can be determined using a redox titration. The half-equation for the oxidation of 4-aminophenol is given below. NH2 NH + 2H+ + 2e HO The oxidizing agent is ammonium cerium(IV) sulfate and ferroin indicator is used to detect the end-point of the titration. During the reaction, the Ce4+ ions are reduced to Ce3+ ions. (i) Write the overall equation for the reaction between Ce4+ ions and 4-aminophenol. (1) 28 *P46661A02832* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br />
(ii) In an experiment, 0.500 g of a tablet containing paracetamol was hydrolysed and the solution was made up to 100 cm3. 20.0 cm3 portions of the resulting solution were titrated with 0.100 mol dm3 ammonium cerium(IV) sulfate solution. The mean titre was 12.60 cm3. Calculate the percentage, by mass, of paracetamol in the tablet. (5) A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D *P46661A02932* 29 Turn over<br />
(d) (i) Identify the chiral carbon atom in ibuprofen with an asterisk (*). (1) OH (ii) Suggest a problem in the manufacture of a single isomer of a chiral drug and describe a way that the pharmaceutical industry might overcome this problem. D O N O T W R I T E I N T H I S A R E A (2)D O N O T W R I T E I N T H I S A R E A (1) (e) Ibuprofen was originally made in a six-step process but is now made in a three-step process. Suggest a specific environmental reason why the manufacturing process was changed.30 *P46661A03032* D O N O T W R I T E I N T H I S A R E A<br />
(f) Ibuprofen is not very soluble in water. It can be made into an ionic, soluble salt by reacting it with lysine. OH OH NH2 NH2 Ibuprofen Lysine Draw the structures of both the cation and the anion in the soluble salt formed when ibuprofen reacts with lysine. (2) (Total for Question 23 = 23 marks) TOTAL FOR SECTION C = 23 MARKS TOTAL FOR PAPER = 90 MARKS A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D *P46661A03132* 31<br />

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Section C Question Number 23(a) Acceptable Answers (acid) amide / N-substituted amide / N- substituted ethanamide / secondary (substituted) amide / substituted amide IGNORE benzene / arene / phenyl Reject Amine / amino acid / carboxylic acid / acid / ester Mark (1) Mark (1) Acceptable Answers Question Number 23(b)(i) (HNO3 + H2SO4H2NO3 + + HSO4 ) Reject base/ acid/ conjugate conjugate acid/ base/ base 1 acid 2 acid 1 base 2 ALLOW any labels that connect the correct acid/base pairs, including linking lines<br />
Acceptable Answers Reject Mark If benzene used instead of phenol OR if final product is not 4-nitrophenol (max 2) ( ) First mark Curly arrow from on or within the circle to the N of NO2 ALLOW curly arrow from anywhere within the hexagon + including ALLOW curly arrow to any part of the NO2 to the + charge (1) Second mark Intermediate structure including charge with horseshoe covering at least 3 carbon atoms and facing the tetrahedral carbon and some part of the positive charge must be within the horseshoe ALLOW dotted horseshoe (1) Third mark Curly arrow from CH bond to anywhere in the hexagon, reforming the delocalised structure (1) IGNORE any involvement of HSO4 Correct Kekule structures score full marks - in the final step (3) Lone pair on N Curly arrow on or outside the hexagon Dotted bonds to H and NO2 unless as part of a 3-D structure Curly arrow from H Question Number 23(b)(ii)<br />
Reject Mark (2) Ring is more electro- negative Reject Hydrogenation Reject ethanoic acid / CH3COOH Mark (1) Mark (1) Acceptable Answers Question Number 23(b)(iv) Reduction ALLOW redox Acceptable Answers Question Number 23(b)(v) ethanoyl chloride / CH3COCl / ethanoic anhydride / (CH3CO)2O If name and formula are given, both must be correct ALLOW displayed / skeletal formulae IGNORE acid chloride / acid anhydride Acceptable Answers Question Number 23(b)(iii) Lone pair of electrons on oxygen (may be shown on a diagram) and EITHER overlaps with pi cloud /delocalised electrons / delocalised system OR Feeds into / donates into / interacts with (benzene) ring /delocalised electrons / delocalised system ALLOW Increases the electron density of the (benzene) ring (1) (Increased electron density) makes the ring more susceptible to electrophilic attack ALLOW phenol is a better nucleophile (1)<br />
ALLOW if this is clearly implied e.g. 4-nitrophenol forms more hydrogen bonds than 2-nitrophenol (1) 4-nitrophenol forms intermolecular hydrogen bonds and 2-nitrophenol forms intramolecular hydrogen bonds (so less intermolecular hydrogen bonds) ALLOW this shown in diagrams / a clear description (1) IGNORE references to other intermolecular forces Reject Mark electrons left in equation (1) Acceptable Answers OR HOC6H4NH2 + 2Ce4+OC6H4NH + 2H+ + 2Ce3+ Acceptable Answers Question Number 23(b)(vi) Hydrogen bonds present in both compounds Reject Mark (2) Question Number 23(c)(i)<br />
Reject Mark Incorrect units once only (5) Acceptable Answers Question Number 23(c)(ii) 95.1(3)% with or without working scores (5) mol Ce4+ used = 12.60x0.100/1000 = 1.260x10-3 (1) mol 4-aminophenol in 20.0 cm3 = 1.260x10-3/2 = 6.30x10-4 TE on mole ratio in (c)(i) (1) mol 4-aminophenol/paracetamol in 100 cm3 = 6.30x10-4 x 5 = 3.15x10-3 TE on mol in 20.0 cm3 (1) mass paracetamol in 100 cm3 = 3.15x10-3 x 151 = 0.47565 (g) TE from mol in 100 cm3 (1) % paracetamol = 0.47565 x 100 0.500 = 95.1(3)(%) TE from mass paracetamol in 100cm3 as long as answer is less than 100% (1) IGNORE SF except 1SF ALLOW alternative methods Acceptable Answers Reject Circle covering additional carbon atoms More than one carbon atom indicated ALLOW other ways of indicating the correct carbon atom eg with a circle Mark (1) Question Number 23(d)(i)<br />
Acceptable Answers Question Number 23(d)(ii) Mark independently Mark (2) Reject Combinatorial chemistry Passing reactants over reagents on polymer supports First mark Any one problem from: Producing a single enantiomer / isomer gives low atom economy / gives (a lot of / 50%) waste / low yield (of required isomer) OR Separating the two enantiomers / isomers is difficult / expensive / uses (a lot of) energy (1) IGNORE just a racemic mixture is formed / unwanted isomer may be harmful / toxic / have side effects Second mark Any one solution from: Produce a single isomer by using enzymes / bacteria / a biological catalyst / a chiral catalyst / chiral synthesis / asymmetric synthesis / stereospecific synthesis OR Use a (natural) chiral molecule as a starting material ALLOW Use of SN2 instead of SN1 (1) IGNORE remove harmful /unwanted products<br />
Acceptable Answers Any one reason from: (The three step synthesis will) Increase atom economy / reduce waste OR Increase / give a higher (percentage) yield OR Use less energy / fuel ALLOW reverse argument for the six step synthesis IGNORE references to costs / raw materials / efficiency / pollution Acceptable Answers Question Number 23(e) Question Number 23(f) OR ALLOW carboxylate ion shown as Reject Mark (1) Mark (2) Reject Charges outside brackets, once only, if both ions are correct and there are no charges inside the bracket ALLOW Anion as shown and the cation with two NH3 groups / cation shown as a protonated zwitterion Anion (1) Cation (1) Total for Section C = 23 marks<br />

Question 20 21 22 23

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