Green Chemistry - Environmental Chemistry

Green chemistry is a strategy for developing chemical processes and products that reduce or eliminate the use and generation of hazardous substances. In order to prevent the introduction of chemical pollutants into the environment, chemical reactions should be designed so that the reactants are completely transformed into useful environmental friendly products by using an environmentally friendly medium.

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What is Green Chemistry?

Green chemistry is defined as the application of a set of principles in the design, manufacture, and use of chemical products to help reduce or eliminate the use or production of hazardous chemicals.

“Sustainable chemistry” is another name for green chemistry.

It is the area of chemistry where the main focus is on improving existing processes or developing new ones with the intention of reducing or eliminating the amount of toxic substances produced in the environment. Environmental chemistry is distinct from green chemistry. Environmental chemistry is concerned with the negative effects of toxic substances on the environment, whereas green chemistry is focused on fostering sustainable development.

The fundamentals ideas of green chemistry includes;

Planning of procedures to increase the amount of raw material that is incorporated into the finished product;
Use of renewable energy and material feedstocks;
Use of solvents and other safe, environmentally friendly materials whenever possible;
Designing processes that are energy-efficient;
The ideal method of waste management is to prevent waste from being produced.

History

Prior to the 1990s, as attention to the issues of chemical pollution and resource depletion increased, green chemistry emerged from a variety of preexisting theories and research endeavors (such as atom economy and catalysis).
Green chemistry’s emergence in Europe and the US coincided with a change in environmental problem-solving tactics.
When the term “green chemistry” began to be used more widely in the mid- to late-1990s, a set of ideas that are now known as such began to come together (which prevailed over competing terms such as “clean” and “sustainable” chemistry).
The Environmental Protection Agency (EPA) played a significant early role in the development of green chemistry in the United States.

12 Principles of Green Chemistry

In the year 1998, Paul Anastas and John C. Warner presented a set of guidelines for green chemistry. The twelve principles have offered a range of options for minimizing the negative effects that chemical manufacturing has on the environment.

Prevention of Waste: It aims at reduction in waste generated rather than cleaning the waste after generation.
Atom economy: It focuses to design such processes that utilize the maximum amount of raw material to make a product.
Avoiding the generation of hazardous chemicals: Various processes should make the minimum use of toxic and harmful substances
The design of safe chemicals: In any process, care must be taken that the chemicals or wastes produced.
Design of safe auxiliaries and solvents: The use of auxiliaries in various chemical processes must be avoided.
Energy efficiency: The energy consumption should be minimized and new processes must be designed that are highly efficient and make the maximum utilization of the energy being used.
Incorporation of renewable feedstock: The processes must make the maximum use of renewable resources and renewable energy and raw materials in order to produce the products.
Reduction in the generation of derivatives: The generation of derivatives must be minimum as they require additional resources to de-toxify them.
Incorporation of Catalysts: Non toxic catalysts must be used as they tend to increase the rate of process and lowers the total energy consumption.
Designing the chemicals for degradation: When creating new products, care must be taken that the product or chemical is non toxic to environment and easily degradable to prevent pollution.
Incorporating real-time analysis: Processes must be monitored in real time and the data must be readily available.
Incorporation of safe chemistry for the prevention of accidents: Thus the chemicals that are being used must be safe to use and handle.

Differentiate Green Chemistry with Pollution Treatment

Green chemistry should not be confused with environmental chemistry because the former deals with different aspects of pollution, its severity, and ways to treat it, whereas the latter does not cause any pollution at all, which is why we say it prevents pollution.

Green chemistry minimizes or eliminates the risks associated with chemical feedstocks, reagents, solvents, and end products in order to reduce pollution at its source.
This contrasts with remediating pollution, which entails cleaning up environmental spills and other releases as well as treating waste streams (end-of-pipe treatment).
Green chemistry is not typically used in remediation processes. Separating potentially dangerous chemicals from other substances, also treating them to make them less dangerous, or concentrating them for safe disposal are all examples of remediation.
Hazardous materials are removed from the environment through remediation, but green chemistry prevents the presence of these materials in the first place.

The use of hazardous chemicals to remove environmental contaminants must be reduced or eliminated for a technology to be considered “green chemistry.” One illustration is substituting a safe sorbent [chemical] for a hazardous one in order to safely remove mercury from the atmosphere. Since the hazardous sorbent is never manufactured when the nonhazardous sorbent is used, the remediation technology satisfies the criteria for green chemistry.

Strategies for Green Synthesis

In order to perform a green chemical synthesis in a lab, the following factors must be taken into account:

Choice of starting material.
Choosing the right solvent or solvents.
Reagent selection
Selection of catalysts
Energy source selection

Choice of starting material

When planning a green chemical synthesis in a lab, it is obvious that the raw materials used in that synthesis itself should come from renewable sources. Petrochemicals are typically used as starting materials in the majority of chemical synthesis. It is planned to replace the use of such chemicals with raw materials of a biological origin to reduce their use because they are non-renewable and require a significant amount of energy. An ideal feedstock (raw material) should, to the greatest extent possible, be renewable, toxic-free, and also capable of being transformed into products in a very limited number of steps.

a. Renewable
b. Having zero toxicity
c. Converted in to products in a very few steps
d. 100 % atom economy
e. 100 % yielding

Choosing the right solvent or solvents

There should be no environmental or health risks associated with the solvent used for a specific reaction. For instance, it is claimed that all organic solvents (VOCs) have a negative impact on human health. Long suspected human carcinogens, halogenated solvents like CH₂Cl₂, CHCl₃, and CCl₄ have also been identified. Alternative solvents have been proposed for use in chemical reactions due to the issues with these solvents.

Hence, it is planned to conduct reactions in water if the use of solvent cannot be avoided. Ionic liquids are another alternative solvent that has been developed. Additionally, supercritical carbon dioxide, water, polyethylene glycol, and its solution have all been used in these organic reactions.

Reagent selection

Efficiency, accessibility, and the reagent’s impact on the environment are taken into consideration when choosing an appropriate reagent for a reaction. The choice of one reagent over another for the same transformation can have an impact on the type of byproducts, yields, etc. Green reagents include:

Dimethyl Carbonate:- The methylation process at the active methylene site
Polymer supported per acids:- They are helpful in epoxidation of alkenes.
Poly NBS:– used as benzylic as well as allylic brominating agent
Polymer supported chromic acid:– used in oxidation of alcohols.
Polystyrene anhydride:– used in acetylation of aniline.

Selection of catalysts

Catalysts are adaptable chemical substances that speed up a reaction without altering it, but not all catalysts are environmentally friendly. Some metal catalysts have a toxic nature and can harm both the biotic environment and the abiotic environment. Thus the term “green catalysts” refers to a variety of catalyst types that have been used. These consist of:

Lewis-acid catalysts are being replaced by acid catalysts, such as microencapsulated catalysts.
For alkylating the benzene rings, simple catalysts like Mgo and -alumina are used.
For instance, the hydroxylation of phenol to catechol, resorcinol, and quinol is carried out using titanium silicate.
The transformations have been carried out using a significant number of photocatalysts. such as photo-catalytic systems based on TiO.
Biocatalysts are also crucial tools for green chemistry.

Examples of Green Chemistry

Green solvents: As technology has advanced, we have developed non-toxic, non-polluting solvents and chemicals. In the past, it was known that the chemicals or solvents used contained chlorine and were harmful to the environment.

Development of new techniques: New, non-toxic, and environmentally friendly methods and procedures are o. The invention of the olefin metathesis reaction by Robert Grubbs, Richard Schrock, and Yves Chauvin, who shared the 2005 Nobel Prize in Chemistry, is an illustration of such a method. Supercritical water oxidation, dry media reactions, and other advancements are examples.

Paper Bleaching: Hydrogen peroxide has taken the place of chlorine in the bleaching of paper. The environment was harmed by the use of chlorine in the past.

Dry cleaning: Tetrachloroethylene, a highly toxic chemical that polluted ground water, was previously used as a dry cleaning agent. It was disease-causing and carcinogenic. Liquid CO₂and a detergent have taken its place as a replacement. Since the waste product produced in this process is liquid carbon dioxide, it ensures that the waste produced is the least toxic possible.

Uses of Green Chemistry

Green chemistry is essential to daily life and has uses across all industries.
It is utilized in a variety of industries, including pharmaceuticals and consumer goods.
It is utilized to create new, more effective processes that are less harmful to the environment.
It is employed in the electrical and electronic industries as well.
Less exposure to endocrine disruptors and other toxic chemicals.
Safer consumer goods of all kinds will be produced: new, safer products will be sold; some products, like drugs, will be produced with less waste; and some products, like pesticides and cleaning supplies, will take the place of less safe alternatives.
Many chemicals are released into the environment either on purpose (like pesticides) while being used, unintentionally (like emissions during manufacturing), or through disposal. Alternatively, green chemicals are also recovered and put to use again after degrading to harmless products.
Fewer synthetic steps, which frequently speed up product production, increase plant capacity, and conserve water and energy.
Chemical processes with higher yields that use less feedstock to produce the same amount of product.
Fewer synthetic steps, which frequently speed up product production, increase plant capacity, and conserve water and energy.
Waste reduction, elimination of pricey remediation, disposal of hazardous waste, and end-of-pipe treatments.

References

Clark, J. H. (1999). “Green chemistry: Challenges and opportunities”. Green Chemistry. doi:10.1039/A807961G
https://www.epa.gov/greenchemistry/basics-green-chemistry
https://byjus.com/chemistry/what-is-green-chemistry/
https://www.studocu.com/in/document/kalinga-institute-of-industrial-technology/environmental-science/green-chemistry-lecture-notes-5/ 17828551
https://www.geeksforgeeks.org/what-is-green-chemistry/
https://www.epa.gov/greenchemistry/benefits-green-chemistry
https://en.wikipedia.org/wiki/Green_chemistry#History
https://pubs.acs.org/doi/abs/10.1021/ar010065m
Clark, J. H.; Luque, R.; Matharu, A. S. (2012). “Green Chemistry, Biofuels, and Biorefinery”. Annual Review of Chemical and Biomolecular Engineering.
https://www.essentialchemicalindustry.org/processes/green-chemistry.html

Green chemistry – Definition, Principles, and Uses