Edexcel Jan 2013 Paper 5 Q16 (with explained solutions) |

Skip to content

Edexcel Jan 2013 Paper 5 Q16

Answers available below

16 Benzenecarboxylic acid (benzoic acid) and phenylmethanol (benzyl alcohol) are compounds which occur naturally and have a wide range of uses. For example, benzenecarboxylic acid is used as a food preservative and phenylmethanol is used as a solvent. A laboratory sequence for the preparation of these two compounds is shown below. HO Step 1 Step 2 benzenecarboxylic acid Step 3 OH phenylmethanol (a) In the first step of the synthesis, benzene reacts with hydrogen chloride and carbon monoxide in the presence of aluminium chloride in an electrophilic substitution called the Gattermann-Koch reaction. The hydrogen chloride and carbon monoxide together behave as if they form the unstable species methanoyl chloride (HCOCl). (i) Explain why benzene undergoes substitution rather than addition reactions. A detailed description of the bonding in benzene is not required. (2)*P41215A01724* 17 Turn over<br />
(ii) Give the mechanism for step 1, including the formation of the electrophile. (iii) Identify the reagents and essential conditions used in the remaining steps of the sequence. You may assume that the correct reaction temperatures are being used. (4) (4) Step 2Step 318 *P41215A01824*<br />
*(b) Phenol reacts faster than phenylmethanol in electrophilic substitution reactions. Suggest why this is so. (4)(Total for Question 16 =14 marks) TOTAL FOR SECTION B = 50 MARKS *P41215A01924* 19 Turn over<br />

Show answer

Acceptable Answers Reject Mark The delocalization of the () electrons of the ring make benzene more stable (than 1,3,5- cyclohexatriene) (1) IGNORE bonding in benzene is strong Substitution retains this (stable) arrangement OR Addition removes this (stable) arrangement (1) Question Number 16(a)(i)<br />
Acceptable Answers Reject Mark Cl Cl Al Cl Cl Cl Cl Al Cl Cl CHO Formation of electrophile (curly arrow, structural formulae not required). Positive charge may be anywhere on the electrophile ALLOW HCl + CO for HCOCl ALLOW Non-displayed electrophile (1) Curly arrow from benzene ring to electrophile (1) Wheland structure with gap opposite tetrahedral carbon (1) Curly arrow from CH bond into ring and formation of correct organic product OR Kekul structures (1) IGNORE Use of AlCl4 Proton product First curly arrow may come from any part of the delocalisation circle Second curly arrow may come from any part of the CH bond Positive charge on the Wheland structure may be in any part of the horseshoeto pick off proton -COH /-HCO Positive charge on the tetrahedral carbon Question Number 16(a)(ii)<br />
Question Number 16(a)(iii) In each step the second mark is dependent on the Acceptable Answers first Step 2 Potassium dichromate((VI)) / K2Cr2O7 / sodium dichromate((VI)) / Na2Cr2O7 ALLOW Potassium manganate ((VII)) / KMnO4 Sodium manganate ((VII)) / NaMnO4 (1) Stand alone mark Sulfuric acid / H2SO4 (ALLOW nitric acid) (1) Ignore concentrated ALLOW Acidified potassium (/ sodium) dichromate((VI)) OR Acid and potassium (/ sodium) dichromate((VI)) (2) Cr2O7 (1) Step 3 Lithium tetrahydridoaluminate((III)) / LiAlH4 OR Lithium aluminium hydride (1) Stand alone mark (Dry) ether / ethoxyethane / (di)ethyl ether (1) Sodium borohydride / NaBH4 in ethanol, alkali or water scores 1/2 (1) 2 and H+ OR acidified dichromate((VI)) Reject Mark Incorrect oxidation number Hydrochloric acid Hydrogen and catalyst / Tin and HCl<br />
Reject Mark Question Number 16(b) Acceptable Answers Marking Point 1 Electron density of the ring increased (1) Stand alone mark Marking Point 2 Due to donation of oxygen / OH group lone pair to the ring (1) Marking Point 3 and 4 Any two from in phenol oxygen / OH group attached directly to ring Oxygen / OH group in phenylmethanol too far away / not attached directly to ring (In phenol) lone pair overlaps with theelectrons / delocalised electrons (of the ring) ALLOW p orbital for lone pair for this mark (2) Total for Q16 = 14 Marks TOTAL FOR SECTION B = 50<br />

Question 14 15 16 17

About us | Need Help? | Feedback

Proudly powered by WordPress | Theme: Sydney by aThemes.