Edexcel Jan 2015 (IAL) Paper 5 Q22 (with explained solutions) |

Skip to content

Edexcel Jan 2015 (IAL) Paper 5 Q22

Answers available below

22 Mandelic acid, 2-hydroxy-2-phenylethanoic acid, has a long history of medical use as an antibiotic and as a component of some cosmetic face creams. It was first obtained from an extract of bitter almonds and Mandel is the German word for almond. Mandelic acid can be synthesized from benzene in the sequence shown below. Stage 2 Stage 1 benzene benzaldehyde OH CH benzaldehyde cyanohydrin Stage 3 OH CH OH mandelic acid (a) (i) Use your knowledge of electrophilic substitution to suggest the identity of the electrophile in Stage 1 of the synthesis. (1)16 *P45045A01628*<br />
(ii) Write the mechanism for the electrophilic substitution in Stage 1, using the electrophile that you have given in (a)(i). (iii) State the reagents and conditions required for Stage 2. You may assume that the reaction is carried out at a suitable temperature. (3) (2)(iv) State the reagent (or reagents) required for Stage 3. (1)*P45045A01728* 17 Turn over<br />
(b) Cyclandelate is a vasodilator (causes blood vessels to dilate) used in the treatment of arteriosclerosis (hardening of artery walls). The structure of cyclandelate is shown below. OH (i) Suggest a single stage synthesis of cyclandelate from mandelic acid. Draw the skeletal formula of the organic compound that would be required and state any essential reagents and conditions. (3)(ii) Suggest a disadvantage of using the synthesis that you have suggested in (b)(i) for the large scale manufacture of cyclandelate. (1)18 *P45045A01828*<br />
(iii) An alternative two stage synthesis of cyclandelate was proposed. This involved reacting mandelic acid with phosphorus(V) chloride. Explain why this suggestion is unsatisfactory. (1)(c) Cyclandelate has three asymmetric carbon atoms. (i) Circle these three asymmetric carbon atoms on the structure below. OH (ii) Explain the possible problem that the presence of asymmetric carbon atoms might cause with the medical applications of cyclandelate. (2) (2)(Total for Question 22 = 16 marks) *P45045A01928* 19 Turn over<br />

Show answer

Reject Mark HCOCl / methanoyl chloride Question Number 22(a)(i) Acceptable Answer OR non-displayed structure (with atoms in any order) ALLOW Positive charge on any part of the structure OR Outside bracketed structure / formula<br />
Reject Mark Curly arrow on or outside the hexagon Dotted bonds to H and CHO unless clearly a dots & wedge 3-D structure COH for CHO Acceptable Answer Question Number 22 (a)(ii) TE on incorrect electrophile in (a)(i) Positive charge on any part of the electrophile Curly arrow from on or within the circle to positively charged carbon ALLOW Curly arrow from anywhere within the hexagon Arrow to any part of the CHO+ including to the + charge Non-displayed electrophile (1) 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 Ignore structure of side chain for this mark (1) Curly arrow from CH bond to anywhere in the benzene ring reforming delocalized fully correct structure including correctly bonded substituent Substituent may be non-displayed (1) Correct Kekul structures score full marks Ignore any involvement of AlX4 formation of the final structure(or similar) in the<br />
Question Number 22(a)(iii) Mark Reject NaOH NaOH Acceptable Answer hydrogen cyanide / HCN (1) potassium (or sodium) cyanide / KCN / NaCN ignore pH = 8 (1) OR KCN / NaCN (1) H2SO4 / HCl ignore concentrations and pH = 8 (1) OR HCN (1) NaOH / pH = 8 (1) ALLOW names or formula throughout Question Number 22(a)(iv) Hydrochloric acid / HCl(aq) Acceptable Answer Reject Mark OR Sulfuric acid / H2SO4(aq) OR sodium hydroxide / NaOH / potassium hydroxide / KOH and followed by any strong acid / H+ ALLOW HCl / H2SO4 / name or formula of any strong acid IGNORE Water / H2O Concentrated Dilute<br />
Question Number 22(b)(i) Acceptable Answer The first two marks are stand alone Mark Reject OH bonded to ring the wrong way around Benzene ring H+ / H3O+ Just heat (1) (Concentrated) sulfuric acid ALLOW Any named strong acid / correct formula with or without state symbol IGNORE Dilute / water (1) (Heat under) reflux (1) Condition mark dependent on the reagent mark being awarded or near miss. Reject Mark Acceptable Answer The esterification / reaction is reversible / an equilibrium (So yield is low) ALLOW Does not go to completion IGNORE References to cost/rate No TE on an incorrect reaction in (b)(i) Acceptable Answer PCl5 reacts with both OH groups Reject Mark Question Number 22(b)(ii) Question Number 22(b)(iii)<br />
Question Number 22(c)(i) Acceptable Answer Reject Mark Mark Reject Geometric / structural isomers Total for Question 22 = 16 marks Question Number 22(c)(ii) Any two from Acceptable Answer All three correct scores 2 marks Two correct from three scores 1 mark More than three circled scores max 1 mark ALLOW Any clear labelling Any ring containing only one correct carbon Only one isomer may be (more) active One isomer (or more) may have a negative effect ALLOW Side effects Different isomers have different (biochemical) properties ALLOW higher dosage required to obtain sufficient amount of active isomer (so expensive) If no other mark is scored Separation of isomers needed OR Low yield can score 1 IGNORE References to just cost<br />

Question 21 22 23 24

About us | Need Help? | Feedback

Proudly powered by WordPress | Theme: Sydney by aThemes.