THE 12 PRINCIPLES OF
GREEN CHEMISTRY – lecture 1
Developed by Paul Anastas and John Warner, the principles outline an early conception of
what would make a greener chemical, process, or product.
1. PREVENTION
2. ATOM ECONOMY
3. LESS HAZARDOUS CHEMICAL SYNTHESES
7. USE OF RENEWABLE FEEDSTOCKS
8. REDUCE DERIVATIVES
9. CATALYSIS
10. DESIGN FOR DEGRADATION
4. DESIGNING SAFER CHEMICALS
11. REAL-TIME ANALYSIS FOR POLLUTION
5. SAFER SOLVENTS AND AUXILIARIES
PREVENTION
12. INHERENTLY BENIGN CHEMISTRY FOR
6. DESIGN FOR ENERGY EFFICICENCY
ACCIDENT PREVENTION
Paul T. Anastas & John C. Warner, Green Chemistry: Theory and Practice, Oxford, 1998, p 30.
1. PREVENTION
“It is better to prevent waste than to treat or clean up waste after it has been created.”
What if we do not generate waste at all?
Manufacturing processes have to try to generate as little waste as possible, through reaction
choice, process design and recycling.
Industry should aim to use chemical reactions and processes that make the most effective
use of available resources and generate the smallest possible amount of waste material.
In this regard, a guiding factor can be the YIELD of a chemical reaction.
The efficiency of a chemical process is indicated by the yield, which compares the expected
product quantity with the actual amount obtained.
>85% - excellent
70 - 85% - good
50 - 70% - moderate
40 - 50% - low
<40% - poor
𝒀𝑰𝑬𝑳𝑫 % =
𝑴𝒂𝒔𝒔 𝒑𝒓𝒐𝒅𝒖𝒄𝒆𝒅
× 𝟏𝟎𝟎 %
𝑴𝒂𝒔𝒔 𝒆𝒙𝒑𝒆𝒄𝒕𝒆𝒅 𝒇𝒓𝒐𝒎 𝒔𝒕𝒐𝒊𝒄𝒉𝒊𝒐𝒎𝒆𝒕𝒓𝒚
An example is the manufacture of phenol
(phenol)
•
The chemical equation shows that 1 mole of benzene (78 g) should yield 1 mole of phenol
(94 g).
•
In practice, the quantity of phenol produced is found to be about 77 g, giving a yield of
82%. (This is a reasonably good yield!)
•
However, the calculation obscures the fact that the reaction also generates 1 mole (126 g)
of sodium sulfite for each mole of phenol produced!
•
This unwanted product may present a serious problem of waste management and adds
significantly to costs.
Bottom line : the yield of chemical reaction is not sole benchmarking criterion.
2. ATOM ECONOMY
“Synthetic methods should be designed to maximize incorporation of all materials used in
the process into the final product.”
It is an alternative measure to yield, and one of the key ideas behind the concepts of green
chemistry.
Atom Economy (AE) expresses the proportion of reactant atoms that end up in a useful
product, measuring the number of atoms of the starting materials that end up as desired
product(s).
σ 𝑀𝑜𝑙𝑎𝑟 𝑀𝑎𝑠𝑠𝑒𝑠 𝑜𝑓 𝑡ℎ𝑒 𝑑𝑒𝑠𝑖𝑟𝑒𝑑 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠
Atom
× 100 %
%=
Economy
σ 𝑀𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠𝑒𝑠 𝑜𝑓 𝑎𝑙𝑙 𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑎𝑛𝑡𝑠
It is important to identify the desired products.
Note: water if a by-product is still a waste as it has other chemicals dissolved/suspended and
requires treatment before reuse.
Q. Calculate the Atom Economy (%) for the following two reactions and predict which one will
be more Green in terms of atom economy principle:
1.
Desired product
2.
Desired product
Here, Ph = C6H5, Cr = 52, S = 32.