Green chemistry is an approach to chemistry that aims to maximize efficiency and minimize hazardous effects on human health and the environment. Definition: Green Chemistry is the use of chemistry for pollution prevention by an environmentally conscious design of chemical products and processes that reduce or eliminate the use or generation of hazardous substances.
The concept
of green chemistry was coined by Paul T. Anastas. Due to the increase in human
population and the industrial revolutions, energy crises and environmental pollution are highlighted as major global problems in the 21st
century. To reduce the impact of energy crisis pollution and to save natural
resources we need to implement 12 principles of green chemistry enunciated by
Paul Anastas wherever possible.
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List the 12 Principles of Green Chemistry
(i)Â Â Prevention
of waste or by-products
(ii)Â Â Â Atom
economy
(iii)Â Â Â Less
hazardous chemicals synthesis
(iv)Â Designing
safer chemicals
(v)Â Â Use
of safer solvents and auxiliaries
(vi)Â Â Â Design
for energy efficiency
(vii)Â Â Use
of renewable feedstocks
(viii)Â Â Reduce
derivatives
(ix)Â Â Â Use
of catalysis
(x)Â Â Â Design
of degradation
(xi)Â Â Real-time
analysis of pollution prevention
(xii)Â Safer
chemistry for accident prevention
Explain Green Chemistry Principles
Sustainable
development can be achieved by adapting the following 12 principles of green
chemistry.
(i) Prevention of waste or by-products
According to this principle of green chemistry, priority is given to the prevention of waste rather than cleaning up and treating waste after it has been generated.Â
Illustration: To develop zero-waste technology (ZWT). As
per ZWT in chemical synthesis, waste products should be zero or minimum. It
also aims to use the waste product of one system as the raw material for another
system.
For Example:
( A) The bottom
ash of thermal power stations can be used as a raw material for the cement and
brick industry.
(B) The
effluent coming out from the cleansing of machinery parts may be used as coolant
water in a thermal power station.
(ii) Atom economy
Atoms
economy is a measure of the number of atoms from the starting materials that
are present in the useful products at the end of the chemical processes.
Good atom
economy means most of the atoms of the reactants are incorporated in the
desired products and only small amounts of unwanted by-products are formed hence lesser problems of waste disposal.
Illustration: The concept of atom economy gives the measure of the unwanted product produced in a particular reaction.Â
% of atom = Formula weight of the desired product/Sum of formula weight of all the reactants used in the reaction X 100
(iii) Less hazardous chemical synthesis
According to this principle of green 'Chemistry,, designed reactions and synthesis routes should be as safe as possible to avoid the formation of hazardous waste from chemical processes.Â
Illustration: Earlier dichlorodiphenyltrichloroethane (DDT) was used as an insecticide and was effective in controlling diseases like typhoid and malaria-carrying mosquitoes. It was realized that (DDT) is harmful to living things. Nowadays, benzene hexachloride(HBC) is used as an insecticide.Â
(iv) Designing safer chemical
The principle of green chemistry aims at developing a product that is less toxic or requires less toxic raw materials. Illustration: In chemical industries workers are exposed to a toxic environment. Safer chemicals must be designed in order to prevent the workers from exposure to toxicity.Â
(v) Use of safer solvents and auxiliaries
This principle of green chemistry involves the use of safer solvents and minimizing the total amount of solvents and auxiliary substances used for any given step of the reaction. This is because solvents and auxiliary substances make up a large percentage of the total waste created.
Illustration: The main aim of this principle is to use green solvents. For example water or supercritical CO2 in place of volatile halogenated organic solvents for chemical synthesis and other purposes. Solvents as chemicals that dissolve solutes and form solutions facilitate many reactions. Water is a safe beginning solvent while dichloromethane is hazardous.
(vi) Design for energy efficiency
According to this principle of green chemistry, chemical synthesis should be designed to minimize the use of energy by carrying out reactions at room temperature and pressure. This can be achieved by the use of proper catalysts, microorganisms for organic synthesis, renewable materials, etc.
Illustration: The biocatalyst can work under ambient conditions. Similarly, in chemical synthesis, refluxing conditions require less energy to improve the technology of the heating system, using microwave heating, etc.
(vii) Use of renewable feedstocks
The perspective of this principle of green chemistry is largely toward petrochemicals. use chemicals that are made from renewable sources rather than other non-renewable sources such as crude oil.
Illustration: Overexploitation of non-renewable feedstocks will deplete the resources and future generations will be deprived and also put a burden on the environment. On the other hand, the use of renewable resources such as agricultural or biological products ensures the sharing of resources by future generations. The practice generally does not put much burden on the environment. The product and waste are generally biodegradable.
(viii) Reduce derivativesÂ
In organic synthesis protecting or blocking groups are commonly used. According to for example installation/removal of the use of protecting groups should be minimized or avoided if possible because such steps require additional reagents and can generate waste.
Illustration: In organic synthesis, protection of some functional groups is required again, the deprotection of functional groups is required at the end. For example Synthesis of m-hydroxybenzoic acid from m-hydroxybenzaldehyde.
The green chemistry principle aims to develop a method where unnecessary steps should be avoided. this can be done if possible by using practicable biocatalytic reactions.
(ix) Use of catalysis
Catalysis is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst that is not consumed in the catalyst reaction and can continue to act repeatedly. thus the use of catalysts in the chemical reaction speeds up its rate and also helps to increase selectivity minimize waste and reduce reaction times and energy demands.
(x) Design for degradation
According to this principle of green chemistry, chemicals are designed in such a way that they are degraded and can be discarded easily. It is ensured that both chemicals and their degradation products are not toxic, bioaccumulated, or environment-persistent.
Illustration: The aim of this principle is that waste products should degrade automatically to clean the environment. Thus biodegradable polymers and pesticides are always preferred. To make separation cashier for the consumer, an international plastic recycle mark is printed on larger items.
(xi) Real-time pollution prevention
This principle of green chemistry focuses on developing analytical methods that allow real-time in-process monitoring and control before the formation of a hazardous substance.
(xii) Safer chemistry for accident prevention
According to this principle of green chemistry, we need to develop a chemical process that is safer and minimizes the risk of accidents.
For example: If the chemical process works with the gaseous substance then the possibility of accidents including explosion is relatively higher compared to the systems working with nonvolatile liquid and solid substances.
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