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Green Chemistry | The 12 Principles Of Green Chemistry
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- Green chemistry aims to reduce chemical related impact on human health and virtually eliminate contamination of the
- environment through dedicated sustainable prevention programs. Green chemistry searches for alternative
- environmentally friendly reaction media and at the same time strives to increase reaction rates and lower reaction
- temperatures. The green chemistry concept applies innovative scientific solutions to solve
- environmental issues posed in the laboratory. Paul T. Anastas, an organic chemist working in the office of
- pollution prevention and toxins at the EPA, and John C. Warner developed the 12 principles of green chemistry in 1991.
- These principles can be grouped into reducing risk and minimizing the environmental footprint. Framework of
- green chemistry. The three main points about the green chemistry framework can be summarized as one, green chemistry
- designs across all stages of the chemical life cycle. Two, green chemistry seeks to design the
- inherent nature of the chemical products and processes to reduce their intrinsic hazard. Three, green chemistry works as
- a cohesive system of principles or design criteria. The 12 principles of green chemistry are design criteria or
- guidelines that provide the framework for sustainable design. They constitute an overarching construct for the design
- of safer chemicals and chemical transformations. Chemistry has long been perceived as a
- dangerous science and often the public associates the word chemical with toxic. There are ways to reduce risk by using
- safety precautions such as protective gear. When safety protections fail, the risk, which is defined as a function of
- the hazard and exposure, increases. If the hazard is high and exposure controls fail, the consequences can be
- catastrophic, injury or death. By minimizing the hazard portion of the equation instead of focusing only on
- exposure controls, the risk can be limited even in cases of undesirable circumstances,
- accident, spills, sabotage, etc. Designing safer, sustainable chemicals and processes requires striving to
- reduce the intrinsic hazards to a minimum and therefore limiting the risk of accidents and damage. The aim of
- green chemistry to reduce hazards across all the life cycle stages is economically profitable. Hazard is
- defined as the ability to cause adverse consequences to humans or the environment.
- Intrinsic hazard of a chemical substance or a chemical process can be designed to be minimized at every level of a
- process. Whether it is toxicity, physical hazards, eg explosion, flammability or global hazards such as
- stratospheric ozone depletion. Risks based on these hazards may arise from the nature of the feed stock and raw
- materials that are used in the chemical transformations as well as the final products that are made.
- Careful design will reduce or eliminate intrinsic hazards within chemicals and processes. A design based on the
- integration of the 12 principles as one cohesive set. The 12 principles of green chemistry were introduced in 1998 by
- Paul Anistas and John Warner. They are a guiding framework for the design of new chemical products and processes applying
- to all aspects of the process life cycle from the raw materials used to the efficiency and safety of the
- transformation, the toxicity and biodegradability of products and reagents used. They were summarized
- recently into the more convenient and memorable acronym productively. The acronym productively summarizes the
- 12 principles of green chemistry. Helping chemists remember key sustainability goals like preventing
- waste, using renewable materials, designing degradable products, using catalysts, ensuring temperature,
- pressure, ambient, monitoring in process. in process, minimizing auxiliary substances, very few,
- maximizing feed, E factor, ensuring low low toxicity, and being inherently yes, safe along with omitting derivatization
- steps and focusing on atom economy implicitly included. One, waste. Waste prevention is the
- first of the 12 principles of green chemistry. It is better to prevent the formation of waste rather than to clean
- it up after the fact. The generation of any material that does not have realized value or the loss of unutilized energy
- can be considered a waste. As mentioned above, waste can take many forms and may impact the environment differently
- depending on its nature, its toxicity, its quantity or the way it is released. When large portions of the initial raw
- materials used in a process are lost because of the original design of the process itself, then it will inexorably
- generate waste which is by definition undesirable. In 1992, the concept of what is now
- widely accepted as the E factor or environmental impact factor was introduced by Roger Sheldon. This metric
- helps to quantify the amount of waste generated per kilogram of product. It is a means to assess the environmental
- acceptability of a manufacturing process. The environmental factor which has been adopted by many in the chemical
- industry underscores how inefficient certain industrial processes have been and opened the door to creative
- solutions. One well-known example is the early synthesis of ethylene oxide which was prepared through a chlorohhydrron
- intermediate. The E factor for the entire synthesis was equal to five. For each kilogram of product, 5 kg of waste
- were to be disposed of. This does not take into consideration the waste water contaminated by chlorine byproducts.
- When the synthesis was modified to use molecular oxygen, thus removing the need for chlorine, the E factor dropped to
- 0.3 kg of waste. The new process was generating more than 16 times less waste than the original one, eliminating the
- formation of waste water as well. Two, atom economy. In 1990, Barry Trust introduced the concept of synthetic
- efficiency. Atom economy AE also called atom efficiency. It refers to the concept of maximizing the use of raw
- materials so that the final product contains the maximum number of atoms from the reactants. The ideal reaction
- would incorporate all of the atoms of the reactants. The AE is measured as the ratio of the molecular weight of the
- desired product over the molecular weights of all reactants used in the reaction. It is a theoretical value
- meant to quickly assess how efficient a reaction will be. Three, synthesis. The synthetic toolbox
- of organic chemists has been improved by a significant amount of innovative work. Many of the new reactions that have been
- developed in the past decade add to the already existing green reactions that were discovered during the past century.
- Reactions based on cylo addition, rearrangement or multicomponent coupling reactions were already known and
- constitute one category of efficient reactions. Cascade or tandem reactions, CH activation, metathesis, and enzyatic
- reactions are rather new approaches and illustrate strong examples of cleaner, more efficient synthetic tools available
- to organic chemists. The Grubs catalyst for example allows alken metaththesis through a mechanism similar to whitig
- type reactions such as the herer wodsworth emens reaction formation of a four-membered ring as reaction
- intermediate. It is an essential tool for the construction of larger molecules.
- However, unlike the witig reaction, the metaththesis reaction does not produce a large amount of waste.
- for molecular design. While there has been significant focus on designing chemicals for various functions ranging
- from medicines to materials, there has been a surprising lack of interest in taking into consideration hazards in the
- design process. Understanding the properties of a molecule that have an impact on the environment and the
- transformations that take place in the biosphere is essential to sustainability.
- Through a mastery of this understanding, chemists will be able to genuinely design molecules that are safer for
- humans and the environment. Work by Aryans in 1984 and by Garrett and Devito in 1996 showed that designing safer
- chemicals is not only highly needed for the advancement of green chemistry, but is also possible. Five, solvents.
- Solvents are perhaps the most active area of green chemistry research. They represent an important challenge for
- green chemistry because they often account for the vast majority of mass wasted in syntheses and processes.
- Moreover, many conventional solvents are toxic, flammable, and/or corrosive. Their volatility and solubility have
- contributed to air, water, and land pollution, have increased the risk of workers exposure, and have led to
- serious accidents. Recovery and reuse, when possible, are often associated with energyintensive distillation and
- sometimes crosscontamination. In an effort to address all those shortcomings, chemists started a search
- for safer solutions. Solventless systems, water, supercritical fluids, SCF, and more recently, ionic liquids
- are some examples of those new green answers. Six, energy. Rising concerns over the depletion of petroleum feed
- stocks and the increase in energy consumption have pushed the development of more energyefficient processes and
- the search for renewable energies, non-depleting resources in a time frame relevant to human scale. As mentioned in
- the first principle, unutilized energy may also be considered a waste. The design of chemical reactions or systems
- that do not require intensive energy use is highly desirable. Reducing the energy barrier of a chemical reaction or
- choosing appropriate reactants so that the transformation may proceed at room temperature is one example of what
- chemists can do to reduce energetic requirements with all the direct and indirect benefits associated with it.
- Seven renewable materials. It has been estimated that the vast majority of our manufacturing products are derived from
- petroleum feed stock or natural gas. The depletion of those resources will touch many aspects of our consumer life and
- our economy. Turning towards renewable feed stocks both for material and fuel has now become more urgent. The major
- renewable feed stock on the planet both for material and energy is biomass. the material available from living
- organisms. This includes wood, crops, agricultural residues, food etc. Examples of renewable material include
- cellulose, lignon, suburin and other wood compounds, polyhydroxyalkcanoes, lactic acid, kiten, starch, glycerol and
- oil. Ligon for instance is a major waste of the pulp and paper industry. Eight derivatives. Coalent derivatization is a
- ubiquitous technique in chemistry whether it is employed for organic synthesis or analytical chemistry. In
- the early 1990s, an innovative concept surfaced called non-covalent derivatization.
- A derivatization that does not rely on coalent bonding but rather on intermolecular interactions.
- The work by Warner was developed as a means to use little energy and less material to achieve chemical
- modifications from the original system. An early example of non-coovalent derivatization is illustrated by the
- controlled diffusion and solubility of hydroquinones used in Polaroid films. Researchers at Polaroid sought to
- release hydroquinones at elevated pH. Instead of relying on base label coalent protecting groups, which would be the
- traditional approach, they developed a non-coovvealent protecting group in the form of a co-crystal between
- hydroquinones and bas n dial terapalomides. This approach was successful and viable
- for the industrial process. It solved the problem without modification of the original hydroquinone structures and
- minimized waste material and energy. Nine catalysis. In many cases, the formation of waste is linked to the
- traditional use of a stoicometric amount of reagents. Switching from stoicometric methodologies to catalytic processes is
- perceived as one major way to improve the efficiency of the synthetic toolbox. Catalysis can improve the efficiency of
- a reaction by lowering the energy input required by avoiding the use of stoicometric amounts of reagents and by
- greater product selectivity. This implies less energy, less feed stock and less waste. 68. Moreover, it often opens
- the door to innovative chemical reactions and brings unconventional solutions to traditional chemical
- challenges. Oxidation and reduction reactions illustrate this concept. Reduction
- employing DIA LH as the hydide donor is a wellestablished procedure used by organic chemists. It generates a
- significant amount of waste since a stoicometric amount of reducing agent is needed to complete the reaction.
- Switching to catalytic hydrogenation like the noori hydrogenation eliminates the need for stoicometric reagents and
- in consequence decreases the amount of feed stock needed and the amount of waste generated. 10. Biodegradation.
- The problem of persistence has been known for a long time and became apparent in the early stages of
- industrial development. In the 1950s, for instance, tetropylene alkalenzene sulfonate TPPs
- was used as a surfactant for laundry detergents and accumulated in the water supply due to incomplete degradation.
- The situation was so critical that there were examples where water tended to foam when coming out of the tap. The public
- outcry prompted the industry to seek an immediate solution and it was found that replacing the methylbranched chain of
- TPPs with a linear carbon chain reduces the bio persistence. A common example is the replacement of
- TPPs by linear alkaallebenzene sulfonate LS 11 analysis. It is the goal of green
- analytical chemistry to measure chemicals without generating waste. The environmental issues associated with
- analytical chemistry are usually linked to the analytical approach itself. Realtime direct analysis is
- unfortunately not systematic as many methodologies still require a pre-treatment of the sample or rely on
- what one may call exitu analysis. Process analytical chemistry is defined as the ability to monitor a
- transformation and act immediately upon it to prevent unwanted outcomes. It is not always possible and therefore waste
- may be generated when the sample is analyzed. Green chemists must take into consideration the functional
- requirements of analytical methods since it will be counterproductive if the chosen methods contribute to further
- environmental problems. Green analytical chemistry can be defined as the use of analytical procedures that generate less
- waste and are safer to human health and the environment. This definition includes both aspects of live monitoring
- of a chemical transformation and the environmental shortcomings associated with traditional analysis.
- In situ, monitoring of a reaction has significant advantages in terms of green chemistry. When action can be taken
- quickly, it may prevent accidents, save energy, and or prevent the formation of significant amounts of byproducts that
- would otherwise require additional purifications. 12. Accident prevention. Dangerous
- substances and processes have multiplied in our working environment. According to the Chemical Accident Prevention and the
- Clean Air Act amendments of 1990, preventing accidents starts by identifying and assessing the hazards.
- All types of hazards, whether it is toxicity, physical hazards such as explosivity or flammability and global
- hazards should be addressed in the design of chemicals and processes to prevent accidents such as Boal or the
- Love Canal incident. A recent and shocking illustration of these dangers and hazards can be found in the UCLA
- accident that occurred in January 2009. Handling of the very common and highly flammable butilythium reagent resulted
- unfortunately in a terrible outcome with the death of the research assistant involved. This accident should be a
- strong reminder to the scientific community that many chemicals we still use present serious hazards and should
- be replaced by safer alternatives to prevent accidents wherever possible. The accomplishments in the field of green
- chemistry thus far are impressive due to the scientists in academia, industry, and research institutes around the
- world. However, the accomplishments achieved thus far are a prelude to the grand challenges still to be addressed
- by the field. A few notable challenges are mentioned below. The design framework of the 12 principles of green
- chemistry has been a template for many advances in the field. However, the 12 principles were not meant to be 12
- independent goals, but rather an integrated cohesive system of design. Only by applying all principles can one
- hope to achieve a truly sustainable process. By seeking out the mutually reinforcing aspects of the principles,
- systemic sustainable design is possible and can facilitate transformative innovation rather than incremental
- improvement. [music]
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