Cover Story
Green Chemistry
Chemistry plays a very important role in most industries as well as in our day today lives. Different types of chemicals are used for various purposes and lots of new compounds are generated by various processes. Any manufacturing process results useful products as well as unavoidable waste products which are harmful to the humans, other living beings and to the environment. Even the useful products can also cause bad effects if they are extensively used or released to the environment in large quantities.
In addition to the chemicals and other substances used in industries, conditions required for some processes also have various harmful effects. Bad effects involve environmental pollution, development of new diseases and loss of biodiversity etc. As a result, there is a necessity of production and usage of greener substances and design and usage of environmentally friendly processes.
Environmental Chemistry is the area of chemistry in which chemistry of natural environment and of pollutant chemicals in nature are concerned. It focuses on chemical phenomena occurred in natural environment. But a new philosophy which mainly focuses on prevention of pollution at its source has developed in the recent past. That is “Green Chemistry”.
What is “Green Chemistry”?
The term green chemistry is defined as:
The invention, design and application of chemical products and processes to reduce or to eliminate the use and generation of hazardous substances.
As the definition of green chemistry implies, it deals not only with the undesirable products generated in the process, but also with the other substances which are used in the process and the process itself. It consists of environmentally friendly, sustainable chemicals and processes whose use results in reduced waste, safer outputs, and reduced or eliminated pollution and environmental damage. It is also called as sustainable chemistry because it encourages innovation and promotes the creation of products that are both environmentally and economically sustainable.
Products, processes and technologies related to green chemistry have a large number of benefits. Some of them are;
· reduced waste
· safer products
· reduced use of energy and resources
· improved competitiveness of chemical manufacturers and their customers.
Green chemistry is a highly effective approach to pollution prevention because it applies innovative scientific solutions to real-world environmental situations. Another important aspect which is highly concerned in green chemistry is risk reduction. In the very basic form, the risk associated with any hazard substance can be evaluated by the product of hazard of that substance and exposure to that matter.
Risk = Hazard * Exposure
Most of the approaches that are used for risk reduction mainly focus on reducing exposure to the hazardous substances. There are various control technologies, treatment technologies and personal protective equipment such as respirators, gloves etc to reduce exposure to the harmful matter and processes. But in green chemistry, risk reduction is achieved through reducing hazard by restricting the use of hazardous chemicals and processes. Thereby it addresses the problems associated with potential failures of exposure controls. The exposure controls are vulnerable to failures since they rely on human activity and equipment in order to reduce risk. In contrast to exposure controls, technologies associated with green chemistry do not depend on humans and equipment, so that the potential failures are reduced. As a consequence, most of the green chemistry options reduce total cost of operations, although some need a high capital investment.
Green chemistry concerns a very broad area of hazards which includes not only the physical hazards such as flammability and explosiveness, but also chronic toxicity, carcinogenicity and global threats such as global warming and stratospheric ozone depletion etc.
Sustainable Chemistry Hierarchy
Chemical products and processes should be designed to the highest level of this hierarchy and be cost-competitive in the market.
- Source Reduction/Prevention of Chemical Hazards
- Design chemical products to be less hazardous to human health and the environment*
- Use feedstocks and reagents that are less hazardous to human health and the environment*
- Design syntheses and other processes to be less energy and materials intensive (high atom economy, low E-factor)
- Use feedstocks derived from annually renewable resources or from abundant waste
- Design chemical products for increased, more facile reuse or recycling
- Reuse or Recycle Chemicals
- Treat Chemicals to Render Them Less Hazardous
- Proper Disposal of Chemicals
· Less toxic to organisms and ecosystems
· Not persistent or bioaccumulative in organisms or the environment
· Inherently safer with respect to handling and use
Twelve Principles of Green Chemistry
There are twelve principles of green chemistry which are developed by Paul Anastas and John Warner and it is originally published in Green Chemistry: Theory and Practice (Oxford University Press: New York, 1998). These principles help to explain what the definition means in practice and cover concepts such as:
- the design of processes to maximize the amount of raw material that ends up in the product;
- the use of safe, environment-benign substances, including solvents, whenever possible;
- the design of energy efficient processes;
- the best form of waste disposal: not to create it in the first place.
Twelve principles* are;
- Prevention
It is better to prevent waste than to treat or clean up waste after it has been created. - Atom Economy
Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product. - Less Hazardous Chemical Syntheses Wherever practicable, synthetic methods should be designed to use and generate substances that possess little or no toxicity to human health and the environment.
- Designing Safer Chemicals
Chemical products should be designed to affect their desired function while minimizing their toxicity. - Safer Solvents and Auxiliaries The use of auxiliary substances (e.g., solvents, separation agents, etc.) should be made unnecessary wherever possible and innocuous when used.
- Design for Energy Efficiency
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. - Use of Renewable Feedstocks
A raw material or feedstock should be renewable rather than depleting whenever technically and economically practicable. - Reduce Derivatives
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. - Catalysis
Catalytic reagents (as selective as possible) are superior to stoichiometric reagents. - Design for Degradation
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. - Real-time analysis for Pollution Prevention
Analytical methodologies need to be further developed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances. - Inherently Safer Chemistry for Accident Prevention
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.
Applications of Green Chemistry
Nowadays researchers’ attention is drawn towards supramolecular chemistry in which solid state reactions are developed, thereby eliminating solvents. If the reactions can proceed in solid state, the usage of solvents, which results various harmful effects, will be reduced.
Another application of green chemistry is synthesis of natural products. Natural product synthesis requires some harsh conditions and it has several bad impacts on environment. But incorporation of principles of green chemistry into these processes eliminates those harsh conditions eliminating hazards. One such example is the new method developed for the synthesis of Tryptanthrin, a biologically active natural product. It is an efficient and green method developed by Atul Kumar and it uses β-cyclodextrin as a catalyst in aqueous media at room temperature.
Since most of the laboratory chemicals are very toxic and harmful, alternatives have been explored for some chemicals. Examples for some toxic chemicals are ethidium bromide, xylene, mercury and formalin and the alternatives have been developed for them.
Green chemistry principles are also applied in organometallic chemistry, where ionic liquids and microreactors were recently used in synthesis and purification of highly reactive organometallic compounds. It has improved safety in operations and efficient production of ultra-high purity organometallics.
When applying green chemistry principles not only the greenness of the process, but the other factors such as chemical yield, the price of reaction components, safety in handling chemicals, hardware demands, energy profile and ease of product workup and purification should also be evaluated. So that, there are several ongoing research projects related to green chemistry.
Various organizations around the world present large number of awards to individuals and businesses for innovations in green chemistry. Examples for such awards are Presidential Green Chemistry Challenge Awards, Australia’s Green Chemistry Challenge Awards and Canadian Green Chemistry Medal etc. That increases the peoples’ concern and interest on green chemistry which eventually leads to the implication of green chemistry technologies that result the usage of environmentally friendly substances and processes.
