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Why is catalysis important in making industrialprocesses more efficient and economically profitable?• Catalytic reagents reduce the energy of thetransition state, thereby reducingWhy is catalysis important in making industrialprocesses more efficient and economically profitable?• Catalytic reagents reduce the energy of thetransition state, thereby reducingWhy is catalysis important in making industrialprocesses more efficient and economically profitable?• Catalytic reagents reduce the energy of thetransition state, thereby reducing

GREEN CHEMISTRY

Why is catalysis important in making industrial

processes more efficient and economically profitable?

• Catalytic reagents reduce the energy of the

transition state, thereby reducing the energy

input required for a process

• Catalysts are required in small quantities

• The regeneration and reversibility of catalysts are good for green processes

No

catalyst

With catalyst

With catalyst: Less energy, less toxic reagents, less waste

5

E factor

• E factor: The actual amount of waste produced in the process (everything but the desired product

except water) / kg of product

• A higher E factor Æ more waste Æ greater

negative environmental effect

• Generally, the E factor increases dramatically on

going from bulk to fine chemicals, and then

pharmaceuticals Å multi-step syntheses +

stoichiometric reagents rather than catalysts for

the latter

For example:

• For examples: Stoichiometric reductions with

metals (Na, Mg, Zn, Fe) and metal hydride

reagents (LiAlH 4 , NaBH 4 )

• Oxidation with KMnO 4 , CrO 3 / H 2 SO 4

• Sulfonations, nitrations, halogenations,

diazotizations and Friedel-Crafts acylations,

employing stoichiometric amounts of mineral

acids (H 2 SO 4 , HF, H 3 PO 4 ) and Lewis acids (AlCl 3 , ZnCl 2 , BF 3 )

Where is the waste from?

Solution to reduce waste?

• Substitution of classical stoichiometric

methodologies with cleaner catalytic alternatives

Catalyst Stoichiometric

reagents

Atom efficiency / economy

No

catalyst

Atom efficiency / economy

Classical aromatic chemistry

Non-classical aromatic chemistry

Two ways to hydroquinone

10 kg waste (MnSO 4 , FeCl 2 , NaCl, Na 2 SO 4 ) / kg

< 1kg waste / kg

Supported catalyst

Solid supports: polymer or silica

• Ill-defined catalytic species

• Limited Range of Reactions

Using solid catalyst

• Less waste

• Less energy consumed

• More possibility to recycle and

reuse

• Cleaner product

Reused catalyst

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Using homogeneous catalyst

Catalyst separation by column chromatography / distillation / extraction

Homogeneous Friedel-Crafts acylation

Heterogeneous Friedel-Crafts acylation

Homogeneous synthesis of

2,6-dichlorobenzonitrile

Heterogeneous synthesis of

2,6-dichlorobenzonitrile – less waste

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Catalyst

Soluble polymer-supported catalyst

Biocatalysts

• Enzymes / whole-cell biocatalysts Æ catalyse organic reactions at pH 4-9, 10-50 o C, without extremes of pressure, addition of metals Æ

environmentally acceptable

• Conventional methods Æ require highly acidic

or basic media, high energy input, toxic metals

Chemo-selectivity:

survive with enzyme

purifications

only

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