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Keith Smith

Emerging Technologies - Sustainable Development. Keith Smith. Centre for Clean Chemistry University of Wales Swansea. Need for Chemicals. Pharmaceuticals and health products. Plastics and other materials for construction and manufacturing. Agriculture - pesticides,

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Keith Smith

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  1. Emerging Technologies - Sustainable Development Keith Smith Centre for Clean Chemistry University of Wales Swansea

  2. Need for Chemicals • Pharmaceuticals and health products • Plastics and other materials for • construction and manufacturing • Agriculture - pesticides, • weed - killers, fertilisers • Fuels and lubricants • Other - paints, dyes, liquid • crystals, specialities, etc.

  3. The World’s Population 1950 2.5 billion 1989 5.2 billion 2050 11 billion?

  4. Concerns and Solutions • Global population growth, leading • to increased consumption • Pollution of the environment, becoming • increasingly controlled • The chemicals/pharmaceuticals industry will come • under increasing pressure to adjust its processes to • ones that are more sustainable • Chemists need to devise new sustainable reactions

  5. Sustainable Development • Renewable energy. • Recycle all products. • Recover all waste. • Use atom efficient reactions. Search for Clean Chemistry

  6. Principles of Clean Chemistry • High yield of a single product. • Replace bulk reactants by catalysts. • Avoid/minimise use of solvent or replace • by water. • Use near - ambient conditions to minimise • fuel use. • Recycle any by-products or waste products.

  7. Electrophilic aromatic substitution • Many commercially important reactions • Acid activators often required • Waste acid streams need treatment • Excess reagents used, often involving heavy • metals or other undesirable materials • Reactions often not regioselective Need for clean chemistry

  8. CH3 CH3 CH3 CH3 NO2 H2SO4 + + HNO3 NO2 toluene NO2 ortho-nitrotoluene meta-nitrotoluene para-nitrotoluene Nitration of Toluene — a Dirty Process Disadvantages: • Yield of para product only about 35%. • Large excess of H2SO4 and excess HNO3 used. • Washes needed, giving large volume of acidic waste - water that has to be treated. • Fuel costs associated with distillation and sulfuric acid recovery.

  9. CH3 CH3 CH3 CH3 NO2 HNO3 + + Ac2O Hß NO2 toluene NO2 ortho-nitrotoluene meta-nitrotoluene para-nitrotoluene The Swansea Nitration Method Advantages: • Yield of para product is about 80%. • The only by-product (acetic acid) is easily recovered. • The H- catalyst can be re-used several times. • No water washing required. • Distillation costs (fuel) reduced.

  10. Comparison of the Old and New Nitration Methods To produce 100 tons para -nitrotoluene tons 200 Old Old 150 Old 100 New New New 50 Toluene required Nitric acid required By-product produced

  11. How the H- Catalyst Works Zeolite  • H- is a solid material known as a zeolite (the word • “zeolite” means “boiling stone”). • Zeolites are Si and Al mixed oxides with associated • cations, such as H+. • The H+ ions mean that zeolites can be strong acids, • making them useful as catalysts. • Zeolites have crystalline porous structures like • a mineral sponge. • The holes in the “sponge” have regular sizes, • with different sizes for different zeolites. • The reaction takes place within the confines of the pores.

  12. CH3 Potential catalytic sites Shape - Selectivity in a Zeolite Pore mainly para-product produced Interaction at a catalytic site favoured for attack at the para-position. REAGENT

  13. Further Nitration of Toluene

  14. Nitration of o-nitrotoluene Nitration is slow using acetic anhydride but quick using TFAA HNO3/TFAA high yield 2 : 1 HNO3/TFAA/Hb high yield 3 : 1 Zeolite has little effect on rate, but enhances selectivity a little Perhaps slowing down the reaction by adding diluent will help

  15. Effect of adding acetic anhydride HNO3/ TFAA/Ac2O 16% 2 : 1 HNO3/TFAA/Ac2O/Hb 99% 17 : 1 Reaction much slower without zeolite Zeolite enhances rate and selectivity substantially o-Nitrotoluene (17.5 mmol), HNO3 (17.5 mmol of 90%), TFAA (3.5 ml, 24 mmol), Ac2O (3.5 ml), Hb (1 g), -10 oC, 2 h

  16. One step dinitration of toluene Literature results: 2HNO3/H2SO4 4 : 1 24HNO3/Ac2O/Claycop/CCl4 85% 9 : 1 HNO3/H/reflux ?% 14 : 1 S.G.Carvalheiro, B.Manuela, P.Laszlo and A.Cornelis, PCT Int Appl, WO 94, 19, 310, 1/9/1994. R. Prins et al., poster at Europacat IV, Rimini, September 1999

  17. One step dinitration of toluene 0.5 g H (17.5 mmol scale) 98% 14 : 1 1.0 g H (17.5 mmol scale) 98% 25 : 1

  18. One pot two step dinitration of toluene 99% overall yield 70 : 1 ca. 3% of other isomers isolated yield 90% with 99% purity K Smith, T Gibbins, R W Millar and R Claridge, J. Chem. Soc., Perkin Trans. 1, 2000, 2753

  19. Another approach to “clean” nitration H Suzuki, S Yonezawa, N Nonoyama and T Mori, J. Chem. Soc., Perkin Trans. 1, 1996, 2385

  20. Modified approach to selective nitration Substrate Yield (%) Proportions ortho meta para toluene 85 53 2 45 benzene 50 -- -- -- fluorobenzene 95 7 0 93 chlorobenzene 95 14 <1 85 bromobenzene 94 22 <1 77 iodobenzene 95 37 1 62 K Smith, S Almeer and S J Black, Chem. Commun., 2000, 1571

  21. CH3 ca. 50% CH3 Br Br2 Fe(cat.) CH3 ca. 50% toluene Br Bromination of Toluene - Traditional Method 1 Advantages: reactants cheap; only one step. Problem: the two products have almost identical boiling temperature, so very difficult to separate — expensive in fuel and time.

  22. CH3 H2SO4 HNO3 CH3 toluene NO2 + CH3 CH3 CH3 NO2 CH3 CH3 + Fe/HCl NaNO2 HCl CuBr NO2 NH2 N2+ Br Cl- Bromination of Toluene Traditional Route 2 Advantage: easy separation at nitro stage; single isomer after. Problems: Low overall yield; several stages, each having its own waste. Easily separated by distillation

  23. CH3 CH3 toluene Br2 Na-Y 99% yield Br heat NaBr + H-Y The protonated catalyst can be re-activated by heating. Bromination of Toluene — a Clean Approach

  24. To produce 100 tons para -bromotoluene tons 600 450 New method Old method possibility 1 Old method possibility 2 300 150 Bromine used Toluene used Other materials used Waste products Comparison of theOldandNewBromination Methods

  25. PEN - an important speciality polymer (PEN is the homopolymer of ethylene glycol with 2,6-naphthalenedicarboxylic acid) Applications of PEN: • Films:(Magnetic recording tapes, flexible printed circuit boards) • Industrial Fibres:(Rubber reinforcement for tyres, hoses and belts) • Packaging:(High acidity foods, carbonated beverages) • Liquid Crystalline Polymers: (Melt-processible thermotropic liquid crystalline polyesters) • Coatings, Inks and Adhesives: (Improvements in flex, surface hardness, etc.)

  26. An interesting problem - selective 2,6-dialkylation of naphthalene (an important PEN intermediate) (a potential precursor)

  27. The nature of the problem Requirements • A high conversion of naphthalene to alkylated products • A high yield of the desired 2,6-dialkylnaphthalene • Very little of any other dialkylnaphthalene, especially 2,7-

  28. Catalyst HM HY HY Naphthalene conversion (%) 74.4 94.0 52.4 DAN (%) 36.3 43.2 27.8 2,6-DAN (%) 25.7 18.6 23.3 5.9 2,6/2,7 3.0 1.2 Reference Kim et al. Applied Catal.A:Gen., 131, 1995, 15. Moreau et al. J. Org. Chem., 57, 1992, 5040. Moreau et al. Applied Catal.A:Gen., 159, 1997, 305. Recently published results for 2,6-dialkylnaphthalene (DAN) selectivity

  29. HY (15) HM (10) HBeta (12) HZSM-5 (25) HMMS (10) Catalyst (Si/Al) 89 22 49 0 Naphthalene conversion (%) 43 45 2 4 0 DTBN (%) 9 33 2 2 0 2,6-DTBN (%) 6 2.7 1.1 - - 1.9 2,6/2,7 Varying the catalyst Preliminary investigation: 2 h autoclave reactions at 160 oC (Catalyst (0.5 g), Nap (10 mmol), ButOH (20 mmol), cyclohexane (100 ml))

  30. Optimisation of the reaction • Increasing the temperature • Increasing the reaction time • Increasing the amount of catalyst • Increasing the amount of tert-butanol • Decreasing the amount of solvent • Increasing the Si/Al ratio • Multistage reactions in 10 ml solvent

  31. 2 4 3 Stage 1 92 97 96 72 Naphthalene conversion (%) 65 64 65 44 DTBN (%) 63 61 62 43 2,6-DTBN (%) 34.8 19.1 25.1 37.1 2,6/2,7 Multistage reactions in 10 ml solvent 1 h autoclave reactions at 180 oC (HM (Si/Al (10) (4.0 g), Nap (10 mmol), ButOH (80 mmol), cyclohexane (10 ml)) Observations: Increases the conversion Maximum yield of DTBN and 2,6-DTBN by 2nd stage Decreases the 2,6/2,7 ratio somewhat

  32. HY HM Catalyst 52.4 96 Naphthalene conversion (%) 27.8 61 DTBN (%) 23.3 60 2,6-DTBN (%) 5.9 50.6 2,6/2,7 Reference P. Moreau et al. Applied Catal.A:Gen., 159, 1997, 305. K. Smith and S.D. Roberts Catalysis Today, 2000, 60, 227-233. Comparison of results for 2,6-di-tert-butylnaphthalene (DTBN) selectivity after optimisation

  33. Conclusions • Nitration of aromatics with very high regioselectivity. • Direct nitration of toluene to 2,4-dinitrotoluene • (near quantitative yield, 2,4:2,6 ratio around 70). • New nitration reaction using N2O4 and O2 over Hb. • Bromination of aromatics with superb regioselectivity. • Selective di-tert-butylation of naphthalene to the 2,6-isomer in 60% yield with a 2,6-:2,7- ratio of over 50.

  34. Thanks The Funding Bodies: Zeneca, EPSRC, DERA, Governments of Qatar and Kuwait, Zeolyst International (for samples) Researchers Adam Musson (Gareth DeBoos) Tracy Gibbins (Ross Millar, Rob Claridge) Saeed Almeer (Steve Black) Dawoud Bahzad Simon D Roberts My Research Group

  35. 1999

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