What is Green Chemistry?

Green chemistry (sometimes referred to as sustainable chemistry) is the branch of chemistry that deals with the design and optimization of processes and products in order to lower, or remove altogether, the production and use of toxic substances. Green chemistry is not the same as environmental chemistry.

The former focuses on the environmental impact of chemistry and the development of sustainable practices that are environment-friendly (such as a reduction in the consumption of non-renewable resources and strategies to control environmental pollution). The latter focuses on the effects that certain toxic or hazardous chemicals have on the environment.

The 12 Key Principles of Green Chemistry

The twelve principles put forward by the American chemists Paul Anastas and John Warner in the year 1998 to lay the foundation for green chemistry are listed below.

• Prevention of waste: Preventing the formation of waste products is always preferable to the clean-up of the waste once it is generated.
• Atom economy: The synthetic processes and methods that are devices through green chemistry must always try to maximise the consumption and incorporation of all the raw materials into the final product. This must strictly be followed in order to minimise the waste generated by any process.
• Avoiding the generation of hazardous chemicals: Reactions and processes that involve the synthesis of certain toxic substances that pose hazards to human health must be optimised in order to prevent the generation of such substances.
• The design of safe chemicals: During the design of chemical products that accomplish a specific function, care must be taken to make the chemical as non-toxic to humans and the environment as possible.
• Design of safe auxiliaries and solvents: The use of auxiliaries in processes must be avoided to the largest possible extent. Even in the circumstances where they absolutely need to be employed, they must be optimized to be as non-hazardous as possible.
• Energy efficiency: The amount of energy consumed by the process must be minimized to the maximum possible extent.
• Incorporation of renewable feedstock: The use of renewable feedstock and renewable raw materials must be preferred over the use of non-renewable ones.
• Reduction in the generation of derivatives: The unnecessary use of derivatives must be minimalized since they tend to require the use of additional reagents and chemicals, resulting in the generation of excess waste.
• Incorporation of Catalysis: In order to reduce the energy requirements of the chemical reactions in the process, the use of chemical catalysts and catalytic reagents must be advocated.
• Designing the chemicals for degradation: When designing a chemical product in order to serve a specific function, care must be taken during the design process to make sure that the chemical is not an environmental pollutant. This can be done by making sure that the chemical breaks down into non-toxic substances.
• Incorporating real-time analysis: Processes and analytical methodologies must be developed to the point that they can offer real-time data for their monitoring. This can enable the involved parties to stop or control the process before toxic/dangerous substances are formed.
• Incorporation of safe chemistry for the prevention of accidents: While designing chemical processes, it is important to make sure that the substances that are used in the processes are safe to use. This can help prevent certain workplace accidents, such as explosions and fires. Furthermore, this can help develop a safer environment for the process to take place in.

Examples of the Impact of Green Chemistry

Use of Green Solvents

Many chemical synthesis reactions that are carried out on an industrial scale require large amounts of chemical solvents. Furthermore, these solvents are also used industrially for degreasing and cleaning purposes. However, many traditional solvents that have been used for such purposes in the past are known to be toxic to human beings. Some such solvents are also known to be chlorinated.

Click here to learn about the different examples of solvents.

The advancement of green chemistry has brought many alternatives to these toxic solvents. The green solvents that are coming up as alternatives are known to be derived from renewable sources and are also known to be biodegradable. Thus, green chemistry has great potential to lower the toxicity of certain industrial environments by developing safer alternatives.

Development of Specialised Synthetic Techniques

The development of specialised synthetic techniques can optimise processes in order to make them more environmentally friendly by making them adhere to the principles of green chemistry. An important example of such an enhanced synthetic technique is the development of the olefin metathesis reaction in the field of organic chemistry. This reaction, developed by Robert Grubbs, Richard Schrock, and Yves Chauvin, won the Nobel Prize for Chemistry in the year 2005.

Other notable developments brought forward by advancements in green chemistry include:

• The employment of supercritical carbon dioxide as a green solvent (as an alternative to other toxic solvents).
• Incorporating the use of hydrogen in enantioselective synthesis reactions (also known as asymmetric synthesis).
• Incorporating aqueous solutions of hydrogen peroxide (a chemical compound with the formula H₂O₂) to drive relatively clean oxidation reactions.

Other notable applications of green chemistry include supercritical water oxidation (often abbreviated to SCWO), dry media reactions (also known as solid-state reactions and solvent fewer reactions), and on water reactions.

Production of Hydrazine

Initially, the most popular method for the production of hydrazine (an inorganic chemical compound with the chemical formula N₂H₄) was the Olin Raschig process, which involved the use of ammonia and sodium hypochlorite. However, with the development of green chemistry, a more environment-friendly alternative to this process was discovered.

In the peroxide process for the production of hydrazine, ammonia is reacted with hydrogen peroxide. In this alternate method, water is produced as the only side product. It can also be noted that the peroxide process does not require any auxiliary extracting solvents.

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