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Keith SmithKeith Smith
Centre for Clean ChemistryCentre for Clean ChemistryUniversity of Wales SwanseaUniversity of Wales Swansea
Emerging Technologies - Sustainable DevelopmentEmerging Technologies - Sustainable Development
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.
19502.5 billion
205011 billion?
19895.2 billion
The World’s Population
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
Sustainable Development
• Renewable energy.Renewable energy.
• Recycle all products.Recycle all products.
• Recover all waste.Recover all waste.
• Use atom efficient reactions.Use atom efficient reactions.
Search for Clean Chemistry
Principles of Clean Chemistry
•High yield of a single product.High yield of a single product.
•Replace bulk reactants by catalysts.Replace bulk reactants by catalysts.
•Avoid/minimise use of solvent or replace Avoid/minimise use of solvent or replace by water.by water.
•Use near - ambient conditions to minimise Use near - ambient conditions to minimise fuel use.fuel use.
•Recycle any by-products or waste products.Recycle any by-products or waste products.
Electrophilic aromatic substitution
• Many commercially important reactionsMany commercially important reactions
• Acid activators often requiredAcid activators often required
• Waste acid streams need treatmentWaste acid streams need treatment
• Excess reagents used, often involving heavyExcess reagents used, often involving heavy metals or other undesirable materials metals or other undesirable materials
• Reactions often not regioselectiveReactions often not regioselective
Need for clean chemistry
Nitration of Toluene — a Dirty Process
Disadvantages:
H2SO4
HNO3
CH3
toluene
CH3
NO2
para-nitrotoluene
+
CH3
NO2
meta-nitrotoluene
+
CH3
NO2
ortho-nitrotoluene
•Yield of para product only about 35%.
•Large excess of H2SO4 and excess HNO3 used.
•Fuel costs associated with distillation and sulfuric acid recovery.
•Washes needed, giving large volume of acidic waste - water that has to be treated.
The Swansea Nitration Method
Advantages:
HNO3
Ac2OHß
CH3
toluene
CH3
NO2
para-nitrotoluene
+
CH3
NO2
meta-nitrotoluene
+
CH3
NO2
ortho-nitrotoluene
•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.
Comparison of the Old and New Nitration Methods
To produce 100 tons para -nitrotoluene
Toluene required Nitric acid required By-product produced
50
100
150
200
tons
Old Old
Old
New
New New
Zeolite
How the H- Catalyst Works
•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.
Potential catalytic sites
Interaction at a catalytic site favoured for attack at the para-position.
mainlymainly parapara-product-product producedproduced
Shape - Selectivity in a Zeolite Pore
CH3 REAGENT
Further Nitration of Toluene
CH3
NO2
CH3
NO2
NO2
O2N
CH3
NO2
NO2
O2N
CH3 CH3
NO2
CH3
NO2
CH3
NO2
+ +
18 3 79
Nitration of o-nitrotolueneCH3 CH3
NO2
NO2NO2
CH3
NO2
+
O2N
HNO3/TFAA/H high yield 3 : 1
HNO3/TFAA high yield 2 : 1
Zeolite has little effect on rate, but enhances selectivity a little
Perhaps slowing down the reaction by adding diluent will help
Nitration is slow using acetic anhydride but quick using TFAA
Effect of adding acetic anhydrideCH3 CH3
NO2
NO2NO2
CH3
NO2
+
O2N
HNO3/TFAA/Ac2O/H 99% 17 : 1
HNO3/ TFAA/Ac2O 16% 2 : 1
Zeolite enhances rate and selectivity substantially
Reaction much slower without zeolite
o-Nitrotoluene (17.5 mmol), HNO3 (17.5 mmol of 90%),TFAA (3.5 ml, 24 mmol), Ac2O (3.5 ml), H(1 g), -10 oC, 2 h
One step dinitration of tolueneCH3 CH3
NO2
NO2
CH3
NO2
+
O2N
2HNO3/H2SO4 4 : 1
24HNO3/Ac2O/Claycop/CCl4 85% 9 : 1
Literature results:
S.G.Carvalheiro, B.Manuela, P.Laszlo and A.Cornelis, PCT Int Appl, WO 94, 19, 310, 1/9/1994.
HNO3/H/reflux ?% 14 : 1
R. Prins et al., poster at Europacat IV, Rimini, September 1999
One step dinitration of toluene
CH3 CH3
NO2
NO2
CH3
NO2
+
O2N2 HNO3
Ac2O
TFAA
H
0.5 g H (17.5 mmol scale) 98% 14 : 1
1.0 g H (17.5 mmol scale) 98% 25 : 1
One pot two step dinitration of toluene
CH3 CH3
NO2
NO2
CH3
NO2
+
O2N
CH3
HNO3
Ac2O
H
HNO3
Ac2O
H
TFAA
NO2
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
Another approach to “clean” nitration
H Suzuki, S Yonezawa, N Nonoyama and T Mori, J. Chem. Soc., Perkin Trans. 1, 1996, 2385
Cl Cl
NO2
Cl
NO2
Cl
NO2
+ +
32 <1 68
N2O4, O2
Fe(acac)3
0 oC, 48 h
Modified approach to selective nitration
X X
NO2
X
NO2
X
NO2
+ +N2O4, O2
0 oC, 48 h
H
Substrate Yield (%) Proportionsortho meta para
toluene 85 53 2 45benzene 50 -- -- --fluorobenzene 95 7 0 93chlorobenzene 95 14 <1 85bromobenzene 94 22 <1 77
iodobenzene 95 37 1 62
K Smith, S Almeer and S J Black, Chem. Commun., 2000, 1571
Bromination of Toluene - Traditional Method 1
Problem: the two products have almost identical boiling temperature, so very difficult to separate — expensive in fuel and time.
Advantages: reactants cheap; only one step.
ca. 50%
ca. 50%
Br2
Fe(cat.)
CH3
toluene
CH3
Br
CH3
Br
CH3
NO2
CH3
NH2
CH3
N2+ Cl-
CH3
Br
H2SO4
HNO3
Fe/HClNaNO2
HCl CuBr
CH3
NO2
+
CH3
NO2
+
Bromination of Toluene Traditional Route 2
Easily separated by distillation
Advantage: easy separation at nitro stage; single isomer after.
Problems: Low overall yield; several stages, each having its own waste.
CH3
toluene
Bromination of Toluene — a Clean Approach
CH3CH3
Br
toluene
Br2
Na-Y 99% yield
NaBr+
H-Y
heat
The protonated catalyst can be re-activated by heating.
Old method possibility 1
Old method possibility 2
New method
To produce 100 tons para -bromotoluene
Bromine used
Toluene used
Waste products
Other materials used
150
450
tons
600
300
Comparison of the Old and New Bromination Methods
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.)
An interesting problem - selective 2,6-dialkylation of naphthalene
CO2Me
MeO2C
R
R
(an important PEN intermediate) (a potential precursor)
R
R
alkylating agent (eg ROH)
catalyst (eg H-form zeolite)
The nature of the problem
Requirements
•A high yield of the desired 2,6-dialkylnaphthalene
•Very little of any other dialkylnaphthalene, especially 2,7-
•A high conversion of naphthalene to alkylated products
alkylating agent (eg ROH)
catalyst (eg H-form zeolite)
alkylating agent (eg ROH)
catalyst (eg H-form zeolite)
alkylating agent (eg ROH)
catalyst (eg H-form zeolite)
alkylating agent (eg ROH)
catalyst (eg H-form zeolite)
Recently published results for 2,6-dialkylnaphthalene (DAN)
selectivity
Catalyst
Naphthaleneconversion (%)
DAN (%)
2,6-DAN (%)
2,6/2,7
Reference
HM
74.4
36.3
25.7
3.0
Kim et al.Applied Catal.A:Gen.,
131, 1995, 15.
HY
94.0
43.2
18.6
1.2
Moreau et al.J. Org. Chem., 57, 1992, 5040.
HY
52.4
27.8
23.3
Moreau et al.Applied Catal.A:Gen.,
159, 1997, 305.
5.9
Preliminary investigation: Varying the catalyst
Catalyst (Si/Al)
Naphthalene conversion (%)
DTBN (%)
2,6-DTBN (%)
2,6/2,7
HY (15)
89
45
33
2.7
HZSM-5 (25)
0
0
0
-
HBeta (12)
49
4
2
1.1
HM (10)
22
2
2
-
HMMS (10)
43
9
6
1.9
2 h autoclave reactions at 160 oC
(Catalyst (0.5 g), Nap (10 mmol), ButOH (20 mmol), cyclohexane (100 ml))
ButOH
•Increasing the temperature
•Increasing the amount of tert-butanol
•Increasing the reaction time
•Increasing the amount of catalyst
•Decreasing the amount of solvent
•Increasing the Si/Al ratio
•Multistage reactions in 10 ml solvent
Optimisation of the reaction
Multistage reactions in 10 ml solvent
Stage
Naphthalene conversion (%)
DTBN (%)
2,6-DTBN (%)
2,6/2,7
4
97
64
61
19.1
1
72
44
43
37.1
3
96
65
62
25.1
2
92
65
63
34.8
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
Comparison of results for 2,6-di-tert-butylnaphthalene (DTBN) selectivity after optimisation
Catalyst
Naphthalene conversion (%)
DTBN (%)
2,6-DTBN (%)
2,6/2,7
Reference P. Moreau et al.Applied Catal.A:Gen.,
159, 1997, 305.
HY
52.4
27.8
23.3
5.9
K. Smith and S.D. RobertsCatalysis Today, 2000, 60, 227-233.
HM
96
61
60
50.6
Conclusions
•New nitration reaction using N2O4 and O2 over H.
•Direct nitration of toluene to 2,4-dinitrotoluene (near quantitative yield, 2,4:2,6 ratio around 70).
•Selective di-tert-butylation of naphthalene to the 2,6-isomer in 60% yield with a 2,6-:2,7- ratio of over 50.
•Bromination of aromatics with superb regioselectivity.
•Nitration of aromatics with very high regioselectivity.
ThanksThanksThe Funding Bodies:Zeneca, EPSRC, DERA, Zeneca, EPSRC, DERA, Governments of Qatar and Kuwait, Governments of Qatar and Kuwait, Zeolyst International (for samples)Zeolyst International (for samples)
The Funding Bodies:Zeneca, EPSRC, DERA, Zeneca, EPSRC, DERA, Governments of Qatar and Kuwait, Governments of Qatar and Kuwait, Zeolyst International (for samples)Zeolyst International (for samples)
Simon D RobertsSimon D Roberts
Tracy Gibbins (Ross Millar, Rob Claridge)Tracy Gibbins (Ross Millar, Rob Claridge)
Saeed Almeer (Steve Black)Saeed Almeer (Steve Black)
My Research GroupMy Research Group
ResearchersAdam Musson (Gareth DeBoos)Adam Musson (Gareth DeBoos)
Dawoud BahzadDawoud Bahzad
1999