The Twelve Principles of Green Chemistry

Featured, Science 2018-06-18

In recent years, the chemicals and engineering industries have been subject to intense pressure and scrutiny from government and regulatory bodies demanding to know the environmental impact of their processes. There is an increased emphasis on making processes cleaner, more environmentally friendly and sustainable.

This is frequently referred to in the industry as focusing on Green and Sustainable Chemistry.

To coincide with our most recent Chemistry World digital supplement, detailing some of the ways companies respond to the needs to make processes more green and sustainable, it is important to answer a simple pressing question: what do green and sustainable chemical practices mean and how does the industry define them?

The definition of Green Chemistry

There are multiple definitions of green chemistry and sustainability. Green chemistry is a concept that exists as an additional pillar of chemistry, alongside the traditional disciplines of organic, physical and inorganic. This applies across the entire lifecycle of a chemical product, from initial synthesis through to decomposition.1 Meanwhile, sustainability has been defined in terms of its impacting factors: environmental, economic and sociological. While all three are certainly important considerations, it is the environmental impact that is perhaps the most important to the general public.

However, the overarching goal of practising green and sustainable chemistry is to develop a world that can continue to support the human race and sustain the needs of the global population.

To achieve this, several leading academics have proposed a series of green chemistry principles that serve as points of thought throughout the development of any industrial process. These are now known as the Twelve Principles of Green Chemistry and were developed in 1998 by Paul Anastas and John Warner,2 before being adopted and widely publicised by the American Chemical Society (ACS) in 2015.

These twelve principles form thought propositions with the aim of improving the design, development and implementation of any industrial process, from fine chemicals production to pharmaceutical development. The principles cover a range of chemical topics and transcend the simple need for non-hazardous materials. Instead, they focus on the major challenges that the industry faces.
Without further ado, let us dive into what the twelve principles are:

1. Prevention

The cleaning and removal of industrial waste can be both challenging and costly. Therefore, it is better to design experiments and processes that do not create copious amounts of waste. Through more careful and considered design of chemical reactions, waste can be prevented.

2. Atom Economy

This principle defines the efficiency of a given chemical reaction. If every atom of every chemical reagent is converted into the final product, then the reaction is considered 100% atom efficient. If this is not possible, then avenues that minimise the production of waste should be investigated to make a reaction as atom efficient as possible. This is both in terms of volume, but also with respect to molecular weight and atomic composition.

3. Less Hazardous Chemical Syntheses

This principle truly speaks for itself. More hazardous chemical reagents or materials are associated with a variety of industrial challenges. This can be in terms of employee safety from handling dangerous substances; environmental hazards in the event of spillages; or the associated increased economic impact associated with the handling of hazardous materials, typically needing specialised facilities and employee training. Therefore, reactions should be designed that synthesise (and handle) minimal amounts of hazardous, toxic or flammable materials.

4. Designing Safer Chemicals

This is somewhat related to the previous principle, but products should also be made as safe as possible. By taking a more considered approach to chemical synthesis, products should be designed that perform the intended function, while being as innocuous as possible.

5. Safer Solvents and Auxiliaries

Chemical reactions are typically performed in the solution phase, requiring a reaction media known as a solvent. For any reactions that use solvent, this must be separated from the desired product after the reaction. However, solvents typically comprise a large proportion of the energy consumed during a reaction process. In addition, common solvents such as toluene, benzene and petroleum ether are associated with various health and environmental issues. Moreover, after the reaction is complete, solvents are recycled (another energy intense process) or incinerated and wasted. Therefore, the use of solvents should be minimised.

6. Design for Energy Efficiency

Performing chemical reactions is an energetically intense process. As is often the case in syntheses, higher temperatures are needed to overcome activation barriers – the energetic cost of initiating a reaction – and provide molecules with sufficient energy to move around the reaction vessel. However, in an ideal situation, all reactions would be performed at room temperature and ambient pressure. While this is not necessarily feasible for all reactions, the energetic requirements must be optimised and minimised as much as possible.

7. Use of Renewable Feedstocks

Again, another principle that speaks for itself. Instead of using chemical reagents that are known as depleting reagents, renewables should be used that are recycled from previous reactions.

8. Reduce Derivatives

When building complex chemicals with a myriad of functional groups, it is essential to direct the reaction down the desired pathway. In order to achieve a direct synthesis, it is common to protect certain functional groups by using blocking groups, in which a functional group is altered into an unreactive entity to prevent an unwanted side reaction. However, this additional step in a given reaction requires additional reagents and energy and can generate waste. Therefore, the use of derivatives should be minimised as much as possible.

9. Catalysis

A catalyst is a chemical substance that accelerates a chemical reaction while not being consumed in the process, meaning one catalyst can be used for multiple chemical syntheses. Catalysed reactions can often result in single-step product formation, to a high degree of activity. This more rapid, selected synthesis results in fewer wasteful by-products, often using milder reaction conditions. These advantages mean that catalyst mediated reactions should be employed where possible.

10. Design for Degradation

Once a chemical has outlived its utility, it needs to be removed and replaced. This principle defines the idea that chemicals should be designed so that when no longer necessary, they can degrade into environmentally innocuous products that do not persist.

11. Real-Time Analysis for Pollution Prevention

As opposed to reactionary pollution monitoring, processes should be developed that facilitate the real-time monitoring of pollutants. This more pre-emptive assessment of the impact of chemical reactions provides further information on the environmental impact of a reaction and the potential hazards that can then be avoided.

12. Inherently Safer Chemistry for Accident Prevention

And finally, substances that are safe to use should be prioritised over unsafe reagents. By choosing appropriate safer substances and chemical reactions, the risk of chemical incidents, including releases, explosions and fires, is reduced.

There we are, the twelve principles that are defined to make chemical synthesis greener, cleaner and more sustainable in the long term. What are your thoughts on green and sustainable chemistry? Let me know at Chemistry World webpage.

References:
1. EPA: The Definition of Green Chemistry
2. Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and Practice, Oxford University Press: New York, 1998, p.30.