What Are the 12 Principles of Green Chemistry?

"It is better to prevent waste than to treat or clean up waste after it has been created."

The principle of waste prevention is to minimize the use of materials, particularly in chemical procedures in environmental testing where byproducts are generated in wastewater. It is important to enforce strict measurements of substances used to reduce chemical waste.

Example: Manufacturing simvastatin through an efficient biocatalytic process

Prof. Yi Tang of the University of California, Los Angeles, led a team in developing a new technique for manufacturing simvastatin, a widely used treatment for high cholesterol. They identified safer and more practical components, such as the biocatalyst LovD and the low-cost acyl donor dimethylbutyryl-S-methylmercaptopropionate.

Moreover, this new method avoids harmful chemicals, such as tert-butyl dimethylsilane chloride, making it economical, practical, and effective in reducing hazardous waste.

"Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product."

Atom economy is similar to the waste prevention principle. However, this time, it focuses on minimizing waste at the atomic scale and maximizing the number of atoms incorporated into the final product.

This principle supersedes yield calculation as a more accurate measure of reaction efficiency. Unlike atom economy, the yield disregards how many atoms from the starting material end up in the product and as waste.

Example: The three-step approach to manufacture ibuprofen

BHC Company developed an efficient method that requires only three catalytic steps compared to the traditional six-step process. BHC's innovation eliminates significant volumes of aqueous salt waste and allows the waste byproduct from the process to be recovered and recycled.

"Wherever practicable, synthetic methods should be designed to use and generate substances that possess little or no toxicity to human health and the environment."

The third principle reminds us to consider human health and the environment when creating substances or chemical products. It also encourages using safer and eco-friendly alternatives to harmful substances in starting materials to limit health hazards and prevent issues with toxic waste disposal.

Example: The membrane cell process in chlorine manufacturing

Before, chemical plants manufactured chlorine with either a mercury or diaphragm cell. Unfortunately, the diaphragm cell contained asbestos, while the mercury cell produced mercury waste.

Since the introduction of cellulose membranes in the 70s, chemical plants have been manufacturing chlorine via a safer membrane cell chloralkali process.

"Chemical products should be designed to affect their desired function while minimizing their toxicity."

The fourth principle is similar to ensuring synthetic methods have minimal adverse effects on humans and the environment. What sets it apart from the previous principle is its focus on maintaining function while reducing toxicity to humans, animals, and the environment.

Example: Replacing petroleum-based solvents with biobased Sefose oils

Procter & Gamble worked with Cook Composites and Polymers Company to develop Chempol MPS paint formulations without utilizing unsafe petroleum-based solvents. Instead, they utilized biobased Sefose oils made from vegetable oil and sugar.

This formulation resulted in high-performance alkyd paints containing less hazardous solvents. When these paints dry, they help reduce indoor fumes and improve air quality.

"The use of auxiliary substances (e.g., solvents, separation agents, etc.) should be made unnecessary wherever possible and innocuous when used."

Solvents and auxiliaries are unavoidable, as many chemical reactions require them. However, they eventually lead to significant solvent waste.

Several green chemistry studies aim to explore safe solvents and develop green solvents that are less flammable, volatile, and explosive.

Example: Creating higher-quality, greener quantum dots

QD Vision succeeded in creating quantum dots, or nanoscale LED components, without incorporating less perilous chemicals and low yields. Their greener system enabled them to manufacture flat-screen displays using less dangerous building blocks and avoid almost 40,000 gallons of highly hazardous solvents yearly.

"Energy requirements of chemical processes should be recognized for their environmental and economic impacts and should be minimized. If possible, synthetic methods should be conducted at ambient temperature and pressure."

Elevated temperatures are necessary for most chemical reactions to take place, requiring substantial amounts of energy. Consuming that much power can have significant environmental impacts, though.

With this, green chemistry discourages processes that require excessive energy. Optimizing reaction design or turning off lab equipment when not in use are effective strategies to minimize energy consumption.

"A raw material or feedstock should be renewable rather than depleting whenever technically and economically practicable."

Various chemical procedures need petrochemicals, or chemical products made from crude oil, as starting materials. The problem with petrochemicals is that they are non-renewable and can be depleted.

Green chemistry advocates for greener processes, including having renewable feedstocks as starting materials. Unlike crude oil-based chemicals, renewable feedstocks come from biological sources and are more sustainable.

Example: Biomass

Biomass is a material derived from living organisms, with plants as an excellent example. Unlike petroleum and other depleting feedstocks, we can grow more plants to produce biobased chemicals once we have consumed them and have a sustainable supply of resources.

"Unnecessary derivatization (use of blocking groups, protection/ deprotection, temporary modification of physical/chemical processes) should be minimized or avoided if possible, because such steps require additional reagents and can generate waste."

Although functional, protecting groups and other derivatives in chemical synthesis require extra reagents and can lead to increased amounts of waste. To apply the eighth principle, researchers have been operating with enzymes instead.

Enzymes function similarly to protecting groups and other derivatives without unnecessary derivatization. In essence, they streamline chemical syntheses and enhance efficiency.

"Catalytic reagents (as selective as possible) are superior to stoichiometric reagents."

Unlike stoichiometric reagents, catalysts can speed up a chemical synthesis without increasing the overall waste generated by the chemical process. Moreover, catalysts remain unaffected by the reaction and can be recycled.

The use of catalytic reagents aligns with other principles of green chemistry, specifically the third and sixth principles, as it promotes energy efficiency and reduces the environmental impact of chemical syntheses.

"Chemical products should be designed so that at the end of their function they break down into innocuous degradation products and do not persist in the environment."

This principle emphasizes the importance of using chemicals or designing chemical products that quickly break down under UV light, water, or biodegradation upon fulfilling their purpose. These chemicals have less adverse environmental impacts than persistent organic pollutants such as halogenated compounds.

Example: Biodegradable Detergents

Manufacturers of laundry detergents use linear alkylbenzene sulfonates (LAS), like sodium dodecylbenzene sulfonate, as a surfactant. LAS quickly degrades when oxygen is present, making it the ideal option over the non-biodegradable branched alkylbenzene sulfonates.

"Analytical methodologies need to be further developed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances."

The 11th principle highlights the need for real-time feedback and to design systems that can be monitored. Real-time analysis allows instantaneous adjustments to ensure the best quality of the product with the least amount of poisonous waste.

In addition, analyzing and monitoring chemical processes in real time promotes safer chemistry as these steps can help prevent the release of pollutants and unsafe substances due to unexpected chemical reactions.

"Substances and the form of a substance used in a chemical process should be chosen to minimize the potential for chemical accidents, including releases, explosions, and fires."

Storing chemicals like oxidizers near flammable materials, improperly labeling chemical products, and neglecting spills inside a laboratory are examples of what the 12th principle of green chemistry addresses.

However, promoting safer chemistry to prevent accidents goes beyond lab safety practices. It also covers unsafe chemicals that have higher risks of harming the environment.

Example: Replacing methyl isocyanate with N-methylformamide

Methyl isocyanate is an organic compound used in rubbers, adhesives, and carbamate pesticides. However, it is a highly toxic gas that could kill thousands of people when released into the atmosphere, similar to what happened to the Bhopal gas tragedy in 1984.

As a solution, chemists recommend N-methylformamide to prevent the risks of harming human health. N-methylformamide, a reagent in organic synthesis, is a safer and less dangerous alternative.

The 12 principles of green chemistry provide a transformative framework for shaping the future of chemistry. They drive innovation toward sustainability by prioritizing safer processes, minimizing waste, and promoting renewable resources.

Adopting green chemistry reduces environmental harm, creates new avenues for collaboration, and produces technological breakthroughs, ensuring safer chemistry.