1

2
“...... Meeting the needs of the present without compromising the ability of future generations to meet their own needs.” http://en.wikipedia.org/wiki/Sustainable_development

3


4
http://en.wikipedia.org/wiki/Green_chemistry
• During the early 1990s,
 the US Environmental Protection Agency
(EPA) coined the phrase “green chemistry”
 promote innovative chemical technologies
 reduce or eliminate the use or generation of hazardous substances in the design, manufacture and use of chemical products

5
http://en.wikipedia.org/wiki/Green_chemistry
Green chemistry is about the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances.
Environmental chemistry is the chemistry of the natural environment, and of pollutant chemicals in nature.
Green chemistry seeks to reduce and prevent pollution at its source.

6
Green Chemistry can also be described as
1. Sustainable chemistry
2. Chemistry that is benign by design
3. Pollution prevention at the molecular level
4. All of the above

7
Green chemistry can be regarded as a reduction process .
It aims at reducing the cost, waste, materials, energy, risk and hazard.
Waste
Cost Materials
Reducing
Risk and hazard
Energy

The Twelve Principles of Green Chemistry:
1. Waste Prevention
2. Maximizing Atom Economy
3. Using Less Hazardous Chemical Syntheses
4. Producing Safer Chemical Products
5. Using Safer Solvents and Auxiliaries
6. Designing for Energy Efficiency
8
7. Using Renewable Raw Materials
8. Reducing Derivatives (fewer steps)

9
The Twelve Principles of Green Chemistry:
9. Using Catalysts
10. Designing Degradable Chemical Products
11. Developing Real-time Analysis for Pollution
Prevention
12. Minimizing the Potential for Chemical
Accidents

It is better to prevent the formation of waste than to treat or clean up the waste.
Chemical wastes are undesirable products from chemical reactions. They are usually hazardous to the environment.
Industrial processes should be designed to minimize the generation of waste.
10

Traditionally, the success of a chemical reaction is judged by the percentage yield of product.
It is possible to achieve 100% yield but the reaction may generate waste that is far greater in mass and volume than that of the desired product.
11

Consider the following reaction:
AgNO
3
(aq) + KCl(aq)  AgCl(s) + KNO
3
(aq)
~100% yield undesirable
12
Suggest reactions that have no undesirable products.
Na(s) + Cl
N
2
(g) + 3H
CH
2
=CH
2
2
(g)
2

(g)  2NH
(g) + H
2
2NaCl(s)
3
(g)  C
(s)
2
H
6
(g)
Direct combination
Addition reaction

13

Mass ofdesired product
Total mass of all products (or reactants)
 100%
The greater the value of the atom economy, the better is the reaction to convert all the reactant atoms to the desired product .
 Less waste

14
Calculate the atom economy of each of the following conversions
C
4
H
9
OH + KBr + H
2
SO
S
4
N
1  racemic mixture
 C
4
H
9
Br + KHSO
4
+ H
2
O
136.9
136.2
18.0
AE 
136.9

136.9
136.2
 18.0
 100%
= 47.0%
3C
4
H
9
OH + PBr
3
 3C
4
H
9
Br + H
3
PO
3
3  136.9
82.0
AE 
3 
3  136.9
136.9
 82.0
 100%
= 83.4%
Non-S
N
Greener

H
3
C
H
C CH
2
+ 2HOCl + Ca(OH)
2
AE 
2 
2  58.0
58.0
 111.0
 2  18.0
 100%
2
H
3
C
H
C CH
2
O
2  58.0
+ CaCl
2
+ 2H
2
O
111.0 2  18.0
= 44.1%
15
H
3
C
H
C CH
2
+ H
2
O
2 catalyst
AE 
58.0
58.0
 18.0
 100%
H
3
C
H
C CH
2
O
58.0
= 76.3%
+ H
2
O
18.0

H
3
C
H
C CH
2
+ 2HOCl + Ca(OH)
2
More harmful
2
H
3
C
H
C CH
2
O
2  58.0
+ CaCl
2
+ 2H
2
O
111.0 2  18.0
H
3
C
C
H
CH
2
+ H
2
O
2 catalyst
Less harmful
H
H
3
C
C CH
2
O
58.0
harmless
+ H
2
O
18.0
Greener
16

Chemical syntheses should be designed to use or generate substances that possess little or no toxicity to humans and the environment.
17

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Consider the synthesis of adipic acid
(HOOC(CH
2
)
4
COOH).
Adipic acid is the essential feedstock for making synthetic fibres such as nylon .
Traditional method
C
6
H
6
HOOC(CH
2
)
4
COOH
New method
C
6
H
12
O
6
HOOC(CH
2
)
4
COOH

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Traditional Method
(1) H
2
, Ni-Al
2
O
3
, 25

55 atm benzene cyclohexane
(2) Co/O
2
, 8

9.5 atm cyclohexanone cyclohexanol
(3) conc. HNO
3 adipic acid dinitrogen oxide

Traditional Method
(1) H
2
, Ni-Al
2
O
3
, 25

55 atm benzene cyclohexane
20
The synthesis has the following risks
(2) Co/O
2
, 8 9.5 atm and hazards:
•
In step 1 , the starting material for the synthesis is benzene , which is a known carcinogen.
dinitrogen adipic acid oxide

Traditional Method
•
In step 2 , the oxidation of cyclohexane
(1) H
2
, Ni-Al
2
O
3
, 25

55 atm with air may lead to an uncontrolled reaction. It has the risk of explosion .
(2) Co/O
2
, 8

9.5 atm
21 cyclohexanone cyclohexanol
•
Not all of the cobalt catalysts can be of a heavy metal to the environment.
dinitrogen oxide

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Traditional Method
•
In step 3 2 , dinitrogen oxide or nitrous oxide ( N
2
O ) gas is produced as a byproduct. It is a greenhouse gas with an effect which is 200 times the effect of carbon dioxide.
cyclohexanol cyclohexanone
(3) conc. HNO
3 adipic acid dinitrogen oxide

biosynthetic pathway
(1) E. coli
2
3
1
(2) E. coli shikimic acid
D-glucose
(3) Pt/H
2
, 3

4 atm
3-dehydroshikimic acid muconic acid
Much greener adipic acid
1. the starting material, glucose, is harmless.
23

biosynthetic pathway
(1) E. coli (2) E. coli
D-glucose 3-dehydroshikimic acid muconic acid
(3) Pt/H
2
, 3

4 atm
Much greener adipic acid
2. E. coli is used to catalyse two steps of the reaction. This reduces the use of certain chemical reagents with significant toxicity.
24

biosynthetic pathway
(1) E. coli (2) E. coli
D-glucose
(3) Pt/H
2
, 3

4 atm
3-dehydroshikimic acid muconic acid
Much greener adipic acid
3. there are no by-products generated during the synthesis.
25

The chemical products synthesized should be safe to use .
26
For example, chemicals called organotin compounds (Anti-biofouling agent) were used in large ships to prevent accumulation of barnacles(
藤壺
) and marine plants traditionally.

27
The accumulation of barnacles(
藤壺
)on the ship may increase the resistance to its movement.

28
However, organotin compounds are highly toxic to the surrounding marine life.
Then, Rohm and Haas Company developed a non-toxic alternative called Sea-Nine TM .
It degrades quickly in the marine environment and is not toxic to the surrounding marine life.

29
The solvents and auxiliaries (e.g. drying agent, blowing agent, etc.) used in chemical syntheses will become part of the wastes.
They may cause environmental pollution and health hazard.

30
CFCs : unreactive volatile liquids or easily liquefied gases low flammability low toxicity
 Cleaning solvents
Propellants
Refrigerants
Blowing agents
They were eventually banned because they deplete the ozone layer .

31
Screening of UV radiations by ozone layer
 =215-295 nm
2O
3
3O
 =250 nm 2
~99% of UV radiation from the sun are screened out

32
They were eventually banned because of their ability to deplete the ozone layer .
CFCl
3
→
Cl  + O
3
CFCl
→
2
+ Cl
ClO + O

2
ClO + O
3
→ Cl  + 2O
2 chain reaction
One Cl  free radical can destroy 100000 ozone molecules

33
Nowadays, CO
2 blowing agent. is used to replace CFCs as the
CO
2 is non-toxic and non-flammable . It does not deplete the ozone layer .
STYROFOAM produced with carbon dioxide as the blowing agent

34
Many solvents currently used in the chemical industry are harmful and volatile
They are known as
V olatile O rganic C ompounds ( VOC s)
E.g. Propanone, benzene, dichloromethane, dibromomethane, chloroform and carbon tetrachloride.
VOCs + NO x
UV photochemical smog

Use safer solvents and auxiliaries – How?
A. Use of water as an environmentally innocuous solvent;
B. Use of liquid or supercritical carbon dioxide;
C. Use of non-volatile solvents: ionic liquids;
D. Use of hybrid solvent systems of the three above;
E. Solvent-less reactions;
35

A. Aqueous Media as Solvents for Chemical
Synthesis and Processes.
Advantages:
– Non-toxic
– Non-flammable
– Inexpensive
– Environmentally benign
Disadvantages:
– Many organic compounds are not soluble in water
36

37
B. Use of liquid or supercritical carbon dioxide
Examples
1. Decaffeination
2.Extraction of essential oil

Using supercritical CO
P / atm
P c
= 73atm
38
2 as solvent in decaffeination
Supercritical fluid
B
C
A
Solid
T
Liquid
Vapour
T c
= 31  C
Gas
CO
2
T /  C

Using supercritical CO
2 as solvent in decaffeination with caffeine without caffeine
In the past, solvents used for decaffeination are harmful to the environment and human beings
E.g. CHCl
3
, CH
2
Cl
2
, benzene
39

Advantages of decaffeination using scCO
2 with caffeine without caffeine
Supercritical CO
2 has
1. the high diffusion of a gas that allows it to penetrate deep into the beans
2. the high density of a liquid that dissolves
97–99% of the caffeine
40

Advantages of decaffeination using scCO
2 with caffeine without caffeine
Will not reinforce the greenhouse effect since scCO
2 comes from the atmospheric CO
2
41

42
Limitations and disadvantages of decaffeination ?
1. Decaffeination is based on solvent extraction (principle of partition equilibrium).
 complete removal of caffeine is not possible
2. Other compounds are lost during the process.
 the flavor and aroma are changed.

43
Essential oils are organic compounds that are extracted from natural sources and used in many products such as flavorings, fragrances, and cleaning products.
Orange peel *
D-limonene
D-limonene : - optically active
- difficult to prepare

Orange peel
D-limonene
44
Traditionally, it was done by organic solvent extraction or steam distillation
Disadvantages :
- VOCs used in solvent extraction are harmful to the environment
- More energy is consumed in steam distillation

45
Orange peel
Liquid CO
2
~5.1 atm
D-limonene
Liquid CO
2 can be obtained easily by allowing dry ice to evaporate in a closed vessel at room temperature.

Liquid CO
2 triple point is easily obtained due to the low pressure at the
P / atm
P c
= 73atm
B
C
Liquid
Solid
5.1 atm T
Vapour
A
46
T c
= 31  C
Supercritical fluid
Gas
CO
2
T /  C

C. Using ionic liquids as solvents
E.g.
N N
BF
4
Low m.p. due to poor packing between ions of significantly different sizes
High b.p. due to ionic nature
 Low volatility
47

N
BF
4 N N
BF
4 N
More viscous
By modifying the structures and charges of the ions, ionic liquids can exhibit specific properties such as m.p., viscosity, volatility & hydrophobicity to meet the particular needs of a synthesis.
48

Advantages of using ionic liquids over using VOCs as solvents (2010 AL Paper 1 Q.6)
1. Tailor-made
2. High b.p.
Not easily escape to the environment
Volatile organic reactants/products can be easily removed by simple distillation.
The solvents can be easily recycled and reused
3. Low flammability due to their low vapour pressure
49

Advantages of using ionic liquids over using VOCs as solvents
4. Wide liquid range due to low m.p. and high b.p.
Organic syntheses can occur at higher temperatures
5. Ionic nature can allow organic syntheses involving ionic species.
50

51
E. Solvent-less reactions
Not easy for reactions involving heating as heat exchange is difficult without a solvent
Solved by microwave heating
Suitable only for polar reactants which are active to microwave.

52
Chemical syntheses should be designed to minimize the use of energy .
Energy is used to raise the temperature of reactants so that a reaction starts or goes on.
heat liquid mixtures for separating and purifying products by distillation.

N
2
(g) + 3H
2
(g) 2NH
Finely divided Fe
3
(g)  H < 0
CATALYTIC
CHAMBER
(450  C) hot compressed
N
2
& H
2
NH
3
, unreacted
N
2
& H
2
53 heat up cool down
N
2
& H
2
HEAT EXCHANGER

54
Ways to conserve energy:
Using catalysts
- reactions at lower T & P
Using microwave heating
- more efficient
Using biosynthetic pathways
- reaction at ambient T & P

55
Reichstein process
Glucose
2-stage fermentation process
Glucose
Sorbitol Sorbitol
Fermentation Fermentation
Sorbose Sorbose Greener
Chemical synthesis
DAKS
(an intermediate compound)
Fermentation
KGA
(an intermediate compound)
Vitamin C

56
Renewable raw materials
They are often made from agricultural products.
E.g. glucose for making adipic acid and vitamin C biodiesel for motor vehicles

57
KOH methanol biodiesel glycerol vegetable oil renewable
Diesel comes from petroleum which is non-renewable
Burns more completely than diesel due to its higher oxygen.

In the production of synthesis gas , natural gas is used as the raw material for the steam-methane reforming process.
CH
4
(g) + H
2
O(g)
700  1000
°
C, 10  20 atm
NiO
From natural gas
3H
2
(g) + CO(g)
Synthesis gas
(or syngas )
58

CH
4
(g) + H
2
O(g)
700  1000
°
C, 10  20 atm
NiO
From natural gas
3H
2
(g) + CO(g)
Synthesis gas
(or syngas )
N
2
(g) + 3H
2
450  C, 200 atm
(g) 2NH
3
Finely divided Fe
(g)
59
2H
2
(g) + CO(g)
250 ° C, 50-100 atm
CH
3
OH(g)
Cu/ZnO/Al
2
O
3
CH
3
Ir based catalyst, HI
OH(g) + CO(g) CH
3
Cativa process
COOH(g)

In the production of synthesis gas , natural gas is used as the raw material for the steam-methane reforming process.
Non-renewable raw material
Replaced by
Natural gas
Renewable raw materials
Landfill methane gas
Paper &
Pig’s manure wood waste
Seaweed
60

Shredded paper (left) and seaweed (right) can be used as the raw materials for the production of synthesis gas
61

62
We should avoid unnecessary use of synthetic steps in order to reduce the derivatives of the desired product.
Otherwise, more reagents are needed and more waste will be generated .

Sato, K.; Aoki, M.; Noyori, 1998
Na
2
WO
4 as catalyst
+ 4H
2
O
2
30%
[CH
3
(n-C
8
H
17
)
3
N]HSO
4 as phase transfer agent
75-90  C, 8h
COOH
COOH
93% yield
+ 4H
2
O
1. One-step synthesis with high yield
2. Proceeds in aqueous medium at relatively low T
3. Reagents and by-product are environmentally benign
63

Bleaching of wood pulp in paper manufacturing
1. H
2
O
2
+ dye H
2
O + (dye + O)
2. OCl  + dye Cl  + (dye + O)
Reaction 1 is greener because it has a higher atom economy it involves less harmful chemicals
64

Bleaching of wood pulp in paper manufacturing
1. H
2
O
2
+ dye H
2
O + (dye + O)
2. OCl  + dye Cl  + (dye + O)
Bleaching with Cl
2 may lead to the formation of dioxin which is an accumulative carcinogen
Cl O Cl
Cl O Cl
65

H
2
O
2
TAML TM catalyst
+ dye H
2
O + (dye + O)
Tetra-Amido Macrocyclic Ligand (TAML) http://en.wikipedia.org/wiki/TAML
- non-toxic iron-based ‘green’ catalysts.
- promote the conversion of hydrogen peroxide into hydroxyl radicals that are involved in the bleaching process
66
- catalyse the oxidation of organic substances in wastewater.

TAML TM catalysts can be used to clean up wastewater streams in the pulp and paper industry
67

Environmental benefits of using TAML TM catalysts in wastewater treatment
68
Decrease in energy requirements
Elimination of chlorinated organic substances
Reduction in water usage
Degradable catalysts

Many chemical products persist in the environment after use.
They should be designed so that they can be broken down into harmless substances .
69

Pesticides
E.g. DDT, they accumulate in plants and animals, causing damage to the final consumers  humans.
70
Designing degradable pesticides that can be decomposed by water, sunlight or micro-organisms .

71
• Several types of degradable plastics:
 biopolymers
 photodegradable plastics
 synthetic biodegradable plastics

72
Biodegradable plastic utensils.
Photodegradable plastic bag.

Real-time monitoring system for
monitoring sulphur dioxide (SO
2
) level
73
When coal is burnt in industrial boilers,
SO
2
(a pollutant) is formed.
If the temperature of the boilers is too high , a large amount of SO
2 will be generated.

74
Real-time monitoring system for
monitoring sulphur dioxide (SO
2
) level
Using real-time monitoring, the amount of
SO
2 time .
generated can be measured all the
Once it reaches an unacceptable level, an alarming signal will be generated. Then the temperature will be lowered immediately .

75
Chemical accidents include leakages , explosions and fires .
Minimize the use of volatile liquids or gases which are associated with the majority of chemical accidents.
If possible, allow reactions to proceed under ambient T & P.