GREEN CHEMISTRY & SUSTAINABLE INDUSTRIAL TECHNOLOGY

Transcription

1 CHE00001M UNIVERSITY OF YORK MSc Examinations 2016 GREEN CHEMISTRY & SUSTAINABLE INDUSTRIAL TECHNOLOGY Time allowed: 2½ hours Answer Section A (Question 1) and TWO out of FOUR questions from Section B Answer all parts of a question unless choice is indicated Allocation of marks is indicated in the right hand margin Databooks and calculators will be provided Turn over/ Page 1 of 10

2 Section A Answer ALL parts in Section A Question 1 (a) Explain why the use of product yield as a way of measuring the efficiency of a chemical reaction is considered to be inadequate in the context of green chemistry. Define the term E-factor and comment critically on its value as a green chemistry metric. A preparation of 4-bromoanisole (BrC 6 H 4 OCH 3 ) is shown below. Calculate the yield and the E-factor, stating any assumptions. Identify one additional factor that would need to be taken into consideration if the process was subjected to a life cycle assessment. (1) (b) One of the principles of green chemistry is that catalysts are superior to stoichiometric reagents. Explain the basis of this principle and illustrate its application with suitable reagents and reactions for: an oxidation reaction; a reduction reaction. Briefly explain how the application of this principle needs to take into account either the criticality of any elements used or the ability to easily recycle and reuse the catalysts. (6) (c) The manufacturing route to the polymer PET is a two-step process as shown below. Identify two potential problems as a result of the strong oxidising conditions used in the first step. Page 2 of 10 Continued...

3 Question 1 continued A "part-bio" PET has recently been prepared using HO(CH 2 ) 2 OH derived from bio-ethanol. Considering only the second step, calculate the "% bio" content in the resulting PET based on: the product; the starting materials. Briefly discuss why it would be difficult to achieve a higher "% bio" content in PET. (d) Critically comment on the statement biomass is a carbon-neutral source of chemicals. Using succinic acid 1 as an example, illustrate the concept of a bioplatform molecule by outlining how green chemical methods can be used to convert succinic acid into two other chemical products. (e) A text-book experimental procedure for the preparation of acetophenone (PhCOCH 3 ) is given below. Place 1 mol of benzene dissolved in 100 cm 3 of dry carbon disulfide in a 500 cm 3 three-necked flask equipped with a condenser fitted with a water trap, mechanical stirrer and separating funnel. Stir and cool the mixture to 5 o C then slowly add 1.2 mol of aluminium chloride followed by 1 mol of acetyl chloride in 50 cm 3 of carbon disulfide over 2 h. Slowly add 100 cm 3 of water cooled to 5 o C. Remove the mixture and place it in a large separating funnel. Remove and discard the aqueous layer then wash the organic layer with an additional cm 3 water. Evaporate the carbon disulfide from the organic layer to leave crude acetophenone product (90%). Write a balanced equation for the reaction to produce acetophenone. (1) Identify four points of concern in the experimental procedure from a green chemistry perspective. For three of your points of concern, suggest improvements with respect to green chemistry. Turn over/ Page 3 of 10

4 Section B Answer TWO questions from Section B Question 2 (a) Propylene carbonate 2 is being developed as a greener polar aprotic solvent to replace traditional polar aprotic solvents. Draw the structures of two traditional polar aprotic solvents and give two reasons why the continued industrial use of this type of solvent may be problematical from a green chemistry perspective. Give a multi-step synthetic route for the synthesis of compound 2 from bioderived propan-2-ol 3 and carbon dioxide, including the reagents for each step and the structures of intermediates. Note: mechanisms are not required. Other than its method of synthesis, give two reasons why propylene carbonate 2 can be considered greener than traditional polar aprotic solvents. (b) The Wacker oxidation normally requires the use of catalytic amounts of both copper(ii) chloride and palladium(ii) chloride. However, the reaction shown below is an example of a Wacker oxidation carried out without the need for copper(ii) chloride. Explain the role of copper(ii) chloride in typical Wacker oxidations and suggest why the use of ethylene carbonate 4 as solvent may allow its use to be avoided in the reaction shown above. Continued... Page 4 of 10

5 Question 2 continued (c) Explain what is meant by the term bioeconomy and give a reason for a move towards the use of renewable feedstocks. Astaxanthin 5 is a dietary supplement that can be extracted from crab, shrimp and lobster as the first step in an aquiculture biorefinery. 5 Describe a suitable green chemistry technology for the extraction of 5 and state two reasons why it would be a suitable technique. Discuss the differences between the production of first generation and second generation biofuels. For each type of biofuel, give one suitable example of a feedstock, conversion technology and the resulting fuel. (5) Turn over/ Page 5 of 10

6 Question 3 (a) A general reaction for the Mn-catalysed oxidation of thioethers to sulfoxides, which can also produce sulfones as unwanted side-products, is shown below. Table 1 gives percentage conversions, sulfoxide:sulfone ratios in the product and the percentages of the metal catalyst recovered after the reaction for different solvents and ionic liquids. Table 1 Solvent or Ionic liquid Conversion / % Sulfoxide : sulfone ratio in the product Metal catalyst recovered after reaction / % Toluene 25 95:5 95 Dioxane 41 80:20 80 Acetonitrile 49 75:25 85 [EMIM][BF 4 ] 77 95:5 95 [EMIM][Tf 2 N] 88 90:10 96 [EMIM][EtSO 4 ] :0 80 [EMIM] + = 1-ethyl-3-methylimidazolium ion; [Tf 2 N] = bis(trifluoromethylsulfonyl)imide ion With reference to the results in Table 1, discuss whether the use of ionic liquids could lead to a greener chemical process for sulfoxide production compared to the use of solvents. Describe one method that could be used to reduce the amount of catalyst lost after the reaction when using the ionic liquids given above, explaining the basis of this method. Name two types of impurities that might be found in a typical sample of [EMIM][BF 4 ] and describe the origin of each. (5) Continued... Page 6 of 10

7 Question 3 continued (b) The biocatalytic synthesis of enantiomerically pure amines such as 6, shown below, in the pharmaceutical industry offers a green chemistry alternative to non-enzymatic reactions, and it can be catalysed by a number of different enzymatic processes. Giving a reaction scheme, describe an industrial route to enantiomerically pure amine 6 that employs a lipase enzyme. Giving a reaction scheme, describe a route to enantiomerically pure amine 6 that employs a transaminase enzyme. Compare and contrast the routes to enantiomerically pure amine 6 that you have described in your answers to parts (b) and (b), commenting on the advantages and disadvantages of each process. Turn over/ Page 7 of 10

8 Question 4 (a) (b) Briefly describe what is meant by the impact assessment stage of a life cycle assessment. Lignin may be produced from biorenewable feedstocks and it may be pyrolysed to give 4-hydroxybenzaldehyde 7, which can be used as a raw material to synthesise biodegradable polymers. One such polymer is 9, produced from 7 via An outline experimental procedure for the synthesis of 9 is given below. A round-bottomed flask was charged with 1,2-dibromoethane, 4-hydroxybenzaldehyde 7, sodium hydroxide, potassium iodide and water. The system was refluxed under a nitrogen atmosphere for 24 hours. The product was isolated by filtration and re-suspended in water for purification. The solid was washed in water-ethanol, isolated by filtration, and vacuum dried to give 8 as a powder. Pentaerythritol, p-toluenesulfonic acid, 1,1,2,2-tetrachloroethane and 8 were added to a flask and refluxed under a nitrogen atmosphere. The water produced was absorbed in anhydrous magnesium sulfate. The white powder remaining in the flask was isolated by filtration, washed with methanol and vacuum dried to give the final polymer 9. Draw a life cycle assessment process flow sheet for the production of biodegradable polymer 9 from 7 using only the data provided in the experimental procedure. (6) Continued... Page 8 of 10

9 Question 4 continued The lignin pyrolysis reaction used to produce 7 gives two other products, vanillin 10 and syringaldehyde Briefly suggest how the environmental impact of products 10 and 11 could be included in a full cradle-to-grave life cycle assessment of the biodegradable polymer 9. (c) Define the European Union chemicals legislation acronym REACH and the European Commission directive acronym IPPC. Briefly discuss the main aim of REACH. Give one example of how REACH might reduce the competitiveness of the European chemical industry in a global market. (1) (d) Polylactic acid (PLA) is an example of a polymer used to make a wide variety of different plastic products. With reference to resources, briefly describe the environmental impact of the production of PLA. Suggest one method that can be used to recycle plastics derived from PLA, and state one advantage and one disadvantage of using this method. Turn over/ Page 9 of 10

10 Question 5 Two routes for the synthesis of stilbene 13 are given below. Route A proceeds from two molecules of benzyl bromide 12. Route B proceeds from iodobenzene 14 and styrene 15. Incomplete results are shown in Table 2. BPS = benzyl phenyl sulfoxide Route A - To a 10 cm 3 round-bottomed flask equipped with a magnetic stirrer bar and condenser was added 12 (0.34 g, 2 mmol), benzyl phenyl sulfoxide (BPS, 0.01 g, 0.05 mmol), potassium tert-butoxide (0.34 g, 3 mmol) and tetrahydrofuran (THF, 3.25 cm 3 ). The reaction was heated to 65 o C for 12 hours, cooled and the mass of 13 determined to be g. Route B - To a 10 cm 3 round-bottomed flask equipped with a magnetic stirrer bar and condenser was added 14 (0.20 g, 1 mmol), 15 (0.16 g, 1.5 mmol), a palladium metal nanoparticle on a support (0.025 g, mmol of active Pd), triethylamine (Et 3 N, 0.20 g, 2 mmol) and dimethylformamide (DMF, 4 cm 3 ). The reaction was heated to 100 o C for 18 hours, cooled and the mass of 13 determined to be g. Note: Densities are: THF d = 0.89 g cm 3, DMF d = 0.95 g cm 3 Table 2 Route Yield Atom economy (AE) Reaction mass efficiency (RME) Optimum efficiency (OE) Process mass intensity (PMI) A 95% 50% 21.1 B 58.4% 82.7% (a) (b) (c) (d) Giving your reasons, identify the reactant(s), reagent, catalyst and solvent for each route. Showing your working, calculate the yield, atom economy (AE), reaction mass efficiency (RME), optimum efficiency (OE) and process mass intensity (PMI) values that are missing from Table 2. For each of AE, RME, OE and PMI, explain the source of the different values between routes A and B. With reference to routes A and B, describe three limitations of mass-based metrics from a green chemistry perspective. (9) END OF EXAMINATION Page 10 of 10