Keith Smith

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

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The Worlds Population
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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

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Sustainable Development

• Renewable energy.

• Recycle all products.

• Recover all waste.

• Use atom efficient reactions.

Search for Clean Chemistry
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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.

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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
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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.

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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.

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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.

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Shape - Selectivity in a Zeolite Pore
mainly para-product
produced
Interaction at a catalytic site favoured for
attack at the para-position.
REAGENT
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Further Nitration of Toluene
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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
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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
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One step dinitration of toluene
Literature results
2HNO3/H2SO4 4
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24HNO3/Ac2O/Claycop/CCl4 85 9
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HNO3/H?/reflux ? 14
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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
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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
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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
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Another approach to clean nitration
H Suzuki, S Yonezawa, N Nonoyama and T Mori, J.
Chem. Soc., Perkin Trans. 1, 1996, 2385
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Modified approach to selective nitration
Substrate Yield () Proportions orth
o meta para toluene 85 53 2
45 benzene 50 -- --
-- fluorobenzene 95 7 0
93 chlorobenzene 95 14 lt1
85 bromobenzene 94 22 lt1
77 iodobenzene 95 37 1 62
K Smith, S Almeer and S J Black, Chem. Commun.,
2000, 1571
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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.
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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
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Bromination of Toluene a Clean Approach
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Comparison of the Old and New Bromination Methods
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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.)

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

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Recently published results for 2,6-dialkylnaphthal
ene (DAN) selectivity
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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))
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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

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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
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Comparison of results for 2,6-di-tert-butylnaphtha
lene (DTBN) selectivity after optimisation
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Conclusions

• Nitration of aromatics with very high
  regioselectivity.

• Direct nitration of toluene to 2,4-dinitrotoluene
• (near quantitative yield, 2,42,6 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.

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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
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1999
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