Week 6, Lesson 3
Chapter 17 – Green Chemistry
Development of CFCs
• Chloroflurocarbons (CFCs) have been identified as
a group of compounds that have contributed to
the deterioration of the ozone layer in the
atmosphere.
• The ozone layer acts as a filter that prevents
some ultraviolet radiation from reaching the
Earth.
• CFCs were first introduced in the 1930’s.
• CFCs were thought to be perfect for refrigeration,
air conditioning and propellants in aerosol cans.
Advantages of CFCs
•
•
•
•
Are non-toxic
Are very stable
Are non-flammable
Can be vapourised at just the right
temperature to make them ideal for
refrigerants
• Made cheaper and safer refrigeration
accessible
CFCs and the Atmosphere
• Scientists became concerned when they
leaked or were released into the atmosphere:
– Their stability meant that they survived for long
periods of time in the environment.
– In the presence of UV light in the atmosphere they
took part in a series of complex reactions that
resulted in the breakdown of ozone in the ozone
layer.
The Solution
• Research identified that the chlorine atom ins
CFCs as the problem.
• Today compounds known as HFCs, which
contain hydrogen, fluoride and carbon are
commonly used.
What is Green Chemistry?
• Green chemistry outlines a set of principles that
forms a framework that can be used to evaluate
the environmental impact of a chemical process.
• It focuses on methods that reduce or eliminate
hazardous waste.
• The green approach is that the best way to
minimise waste is to not produce it in the first
place.
• Its ultimate goal is to implement energy-efficient,
hazard-free, waste-free, efficient chemical
processes without sacrificing their effectiveness.
Green Chemistry
• Ideally:
– Goods needed by society should be produced by
methods that are not harmful to the environment
– Fossil fuels and other non-renewable resources
should be replaced by renewable ones
– Goods produced by society should either be
recyclable or biodegradable
– The processes used to manufacture the product
should either produce no wastes or wastes that
are recyclable or biodegradable.
Principles of Green Chemistry (1-3)
1. PREVENT WASTE – it is better to design
chemical processes to prevent waste than to
treat waste or clean it up after it is formed.
2. DESIGN SAFER CHEMICALS AND PRODUCTS –
design chemical products to be fully
effective, yet have little or no toxicity.
3. DESIGN LESS HAZARDOUS CHEMICAL
SYNTHESES – Methods should be designed
that use and generate substances with little
or no toxicity to humans and the
environment.
Principles of Green Chemistry (4-6)
4. USE RENEWABLE RAW MATERIALS – Use starting materials
that are derived from renewable resources such as plant
material rather than those such as from fossil fuels that will
eventually run out.
5. USE CATALYSTS, NOT STOICHIOMETRIC REAGENTS – Minimise
waste by using catalysts in small amounts that can carry out a
single reaction many times. They are preferable to
stoichiometric reagents, which are used in excess and work
only once.
6. AVOID CHEMICAL DERIVATIVES – Avoid using blocking or
protecting groups or any temporary modifications if possible.
Derivatives use additional reagents and generate waste.
Principles of Green Chemistry (7-9)
7. MAXIMISE ATOM ECONOMY – Design syntheses so
that the final product contains the maximum
proportion of the starting materials. There should be
few, if any, wasted atoms.
8. USE SAFER SOLVENTS AND REACTION CONDITIONS –
Avoid using toxic solvents to dissolve reactants or
extract products.
9. INCREASE ENERGY EFFICIENCY – Energy
requirements should be minimised. Run chemical
reactions at room temperature and pressure
whenever possible.
Principles of Green Chemistry (1012)
10. DESIGN FOR DEGRADATION – Chemical products should be
designed to break down harmless substances after use so that
they do not accumulate in the environment.
11. ANALYSE IN REAL TIME TO PREVENT POLLUTION – Include
continuous monitoring and control during process to minimise
or eliminate the formation of by-products.
12. MINIMISE THE POTENTIAL FOR ACCIDENTS – Design
chemicals and their forms (solid, liquid or gas) to minimise the
potential for chemical accidents including explosions, fires
and releases to the environment.
Atom Economy
• The atom economy approach is a method of
accounting for the use of materials in a
manufacturing process.
• It tracks all atoms in a reaction and calculates
the mass of the atoms of reactants actually
used to form products as a percentage of the
total mass of reactants.
• From this, the mass of reactant atoms that
end up as waste can be calculated.
Atom Economy Example…
• Calculate the percentage atom economy in the formation of
1-iodiopropane from 1-propanol according to the following
reaction.
CH3CH2CH3OH + NaI + H2SO4  CH2CH2CH2I + NaHSO4 + H2O
Formula of
Reactants
Molar Mass Atoms used
of Reactants in Product
Sum of
Molar Mass
of Used
Atoms
Unused
Atoms
Sum of
Molar Mass
of Unused
Atoms
CH3CH2CH2O 60.1
H
3C, 7H
43.1
HO
17.0
NaI
149.9
I
126.9
Na
23.0
H2SO4
98.0
-
0
2H, S, 4O
98.0
3C, 7H, I
170.0
HO, Na, 2H,
S, 4O
138.0
Total Atoms 308.0
in
Reactants,
3C, 10H, 5O,
Atom Economy Example
Continued….
Percentage Atom Economy = (molar mass used atoms / molar
mass of all reactants) x 100
= (170.0/308.0) x 100
= 55.2%
Formula of
Reactants
Molar Mass Atoms used in
of Reactants Product
Sum of Molar
Mass of Used
Atoms
Unused
Atoms
Sum of Molar
Mass of
Unused
Atoms
CH3CH2CH2OH 60.1
3C, 7H
43.1
HO
17.0
NaI
149.9
I
126.9
Na
23.0
H2SO4
98.0
-
0
2H, S, 4O
98.0
3C, 7H, I
170.0
HO, Na, 2H, S,
4O
138.0
Total Atoms in 308.0
Reactants, 3C,
10H, 5O, Na,
S, I
Green Chemistry in Action
• Most commonly used solvents are flammable
and volatile organic compounds which are
toxic.
• Some have significant environmental impact
and are associated with the deterioration of
the ozone.
• There has been a lot of research in finding
alternative solvents.
• One alternative is carbon dioxide.
Supercritical Carbon Dioxide
(scCO2)
• Usually when liquids are heated they turn into a vapour and
when vapour is compressed it condenses into a liquid.
• However, if a vapour is heated above a certain critical
temperature, the vapour cannot be liquefied no matter what
pressure is applied.
• At these temperatures the distinction between liquid and gas
is blurred.
• The material has similar properties to gas in that it expands to
fill any space, however, it also has similar properties to a liquid
and can be used as a solvent.
• At this stage, the material is said to be a supercritical liquid.
Supercritical Carbon Dioxide cont…
• Carbon dioxide forms a supercritical fluid at a
pressure of 73atm and a temperature of 31°C.
• This relatively low temperature makes superficial
carbon dioxide easy to work with.
• Another useful feature is that its solvent properties
can be altered by making slight adjustments to
temperature and pressure.
• scCO2 is an environmentally friendly option also
because it can be obtained as a by-product from
other industries. It is also easy to recapture and
rescue.
Other examples of Green
Chemistry
• Petroleum is the raw material for the manufacture of
polystylerene. Polystyrene is a very good heat insulator and
shocker absorber so is commonly used in food containers nad
packaging.
• In the past, this packaging was expanded with the use of CFCs.
Now these have been replaced with CO2 or restaurants are
using cardboard containers.
• Adipic acid is a compound used in large quantities to make
nylon and other useful products. Usually this is made from
benzene, a known carcinogen.
• Scientists have found a way, by using genetically altered
bacteria as catalysts to make adipic acid from glucose.