What probably brought you here was a subject having the rather weighty word 'environmental' in it's title. But one may note, there is a distinction between Environmental and Green Chemistry. They are two different aspects of environmental pollution studies.
Environmental chemistry is the study of the natural environment and the pollutants that plague it. Green chemistry is also called sustainable chemistry and aims to minimize or eliminate the use and generation of hazardous substances.
Let us elaborate on the fundamental concept of sustainability to get a clearer picture.
Chemistry has improved our quality of life and made thousands of products possible. Unfortunately, this achievement has come at a price: our collective human health and the global environment are threatened. Our bodies are contaminated with a large number of synthetic industrial chemicals, many of which are known to be toxic and carcinogenic while others remain untested for their health effects. Many chemicals work their way up the food chain and circulate round the globe; pesticides used in the tropics are commonly found in the Arctic; flame retardants used in furniture and electronics are now commonly found in marine mammals. Yet as cancer rates rise and evidence increases about the link between certain chemicals and birth defects and learning disabilities our regulatory system has been unable to make chemical producers provide full testing information or promote inherently safer chemicals. They can destroy natural resources and especially the means of livelihood for future generations. In addition, many feedstocks for the production of chemicals are based on petroleum, which is not a renewable resource.
The key question to address is: what alternatives can be developed and used? In addition, we must ensure that future generations can also use these new alternatives. "Sustainability" is a concept that is used to distinguish methods and processes that can ensure the long-term productivity of the environment, so that we may satisfy the need of the present generations without compromising the ability of the future generations to satisfy theirs.
One striking example of a sustainable society can be seen in this documentary: Satoyama: Japan's Secret Water Garden II
Green chemistry applies to organic chemistry, inorganic chemistry, biochemistry, analytical chemistry, and even physical chemistry. The concept of invention and design is the soul of this discipline.
The term Green Chemistry was coined in 1991 by Paul Anastas of the U.S. Environmental Protection Agency so let's have a look at the list the Green chemical principles formulated by him :
1. Waste prevention instead of remediation - It is better to prevent waste than to treat or clean up waste after it is formed. Along the lines of the age old saying, 'Prevention is better than cure'.
2. Atom economy or efficiency - concept that evaluates the efficiency of a chemical transformation.
% Atom Economy = No. of atoms incorporated x 100.
No. of atoms in the reactants
Choosing transformations that incorporate most of the starting materials into the product are more efficient and minimize waste. Diels–Alder reaction (between a conjugated diene and a substituted alkene, to form a substituted cyclohexene system) is 100% atom economy reaction as all the atoms of the reactants are incorporated in the cycloadduct.
3. Use of less hazardous and toxic chemicals - This principle focuses on choosing reagents and synthetic methodologies that pose the least risk and generate only benign by-products that possess little or no threat to human health and environment.
For example, in the manufacture of polystyrene foam sheet packing material chlorofluorocarbons (which contribute to O3 depletion, global warming and ground level smog) have now been replaced by CO2 as the blooming agent.
4. Safer products by design - A pertinent example of smarter production is metathesis which was developed by Grubbs, Schrock and Chauvin. It is a reaction in which double bonds are broken and made between carbon atoms in ways that cause atom groups to change places,with the help of special catalyst molecules. It is used in the development of pharmaceuticals and advanced plastic materials, and is a great step forward for green chemistry.
To know more about this Nobel Prize winning contribution, click on : http://en.wikipedia.org/wiki/Olefin_metathesis
5. Innocuous solvents and auxiliaries - Solvents are extensively used in most of the syntheses. Widely used solvents in syntheses are toxic and volatile – alcohol, benzene (known carcinogenic), CCl4, CHCl3, perchloroethylene, CH2Cl2. Purification steps also utilize and generate large amounts of solvent and other wastes (e.g., chromatography supports). These have now been replaced by safer green solvents like :
a) Ionic liquids are liquids at RT and below. They are non volatile and have no vapour pressure. They can serve as optimal replacements for volatile organic traditionally used industrial solvents. The reactions in ionic liquids need no special apparatus and methodologies, and they can be recycled.
b) Supercritical CO2 fluid is now becoming an important commercial and industrial solvent for chemical separation because of its low toxicity and non-inflammability.
c) Supercritical water: Many organic compounds become soluble in water when it becomes supercritical at 374oC and 218atm. Hence, it is used as a clean and cheap solvent.
d) Reactions in aqueous phase: Replacement of organic solvents with eco-friendly water has found success with many reactions,some of which may occur at higher rates because of its high polarity. They include oxidations, reductions, epoxidations, polymerizations (with or without catalysts) and many named reactions.
e) Reactions in solid phase: Large number of reactions occuring in solid state, without the solvent, utilize the surfaces or interiors of clays, zeolites, silica, and alumina.These reactions are simple to operate, economical and solvent-related pollution is avoided.
6. Energy efficiency by design - Energy requirements of the chemical processes should be recognized for their environmental and economic impacts and should be kept to a minimum.
a) Microwave irradiation: Reactions with microwave sources have been carried out in a solid support like clay, silica gel, etc., eliminating or minimizing the use of solvents. The reactions take place at a faster rate than thermal heating. For example Beckmann rearrangement of oximes in the solid state with microwave irradiation gave quantitative yields of the products without the use of acid catalysts.
b) Sonochemistry (Ultrasound energy): Reactions using ultra- sound energy are carried out at RT with excellent yields. For example, Ullmann’s coupling which takes place at higher temperature giving low yields by conventional method, gives increased yields at low temperature and in short duration with ultra sound energy.
7. Preferred use of renewable raw materials - It is preferred to utilize raw materials and feedstocks that are renewable, but technically and economically practicable. Citing the example of renewable feedstocks which include agricultural products, and those of depleting feedstocks include raw materials that are mined or generated from fossil fuels (petroleum, natural gas or coal). For green synthesis, the feedstock should replace the traditional petroleum sources, e.g. benzene used in the commercial synthesis of adipic acid which is required in the manufacture of nylon, placticizers and lubricants, has been replaced to some extent by the renewable and non-toxic glucose and the reaction is carried out in water.
8. Shorter syntheses (avoid derivatization) - 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 more waste. Instead more selective and better alternative synthetic sequences that eliminate the need for functional group protection should be adopted.
This improved synthesis won the Presidential Green Chemistry Challenge Greener Synthetic Pathways Award in 1997.
9. Catalytic rather than stoichiometric reagents - Catalysts are used in small amounts and can carry out a single reaction many times and so are preferable to stoichiometric reagents, which are used in excess and work only once. They can enhance the selectivity of a reaction, reduce the temperature of a transformation, reduce reagent based waste and potentially avoid unwanted side reactions leading to a clean technology. Apart from heavy metal catalysts softer catalysts like zeolites, phase transfer catalysts, (e.g., crown ethers), are finding increasing industrial applications.
10. Design products to undergo degradation in the environment - They should not accumulate and persist in the environment but break down into innocuous hazardless substances at the end of their function.
11. Inherently safer processes - Design chemicals and their forms (solid, liquid, or gas) to minimize the chemical accidents including explosions, fires and releases to the environment.
Example, manufacture of gold atom nanoparticles used diborane (highly toxic and bursts into flame near room temperature) and cancer-causing benzene. Now, diborane has been replaced by environmentally benign NaBH4 which also eliminates the use of benzene.
Nanoscience and nanotechnology is another important contribution to green chemistry. Nanotechnology provides huge savings in materials by development of microscopic and submicroscopic electronic and mechanical devices.
12. Analytical methodologies for pollution prevention - Instances elucidate best.
a) The most polluting reaction in industry is oxidation. Implementation of green chemistry has led to the use of alternative less polluting reagents viz. metal ion contamination is minimized by using molecular O2 as the primary oxidant and use of extremely high oxidation state transition metal complexes.
b) Conventional methylation reactions employing toxic alkyl halides or methylsulfate leading to environmental hazard are replaced by dimethyl carbonate with no deposit of inorganic salts e.g., methylation of arylacetonitriles in presence of K2CO3 to 2- arylpropionitriles (> 99%).
(Click here to download a pdf file about the chemistry of dimethyl carbonate)
c) In the synthesis of polycarbonates use of phosgene and methylene chloride has been replaced by diphenyl carbonate.
d) Use of CO2 as a reaction medium for asymmetric catalytic reductions particularly hydrogenation and H2 transfer reactions.
e) A convenient green synthesis of acetaldehyde is by Wacker-chemie’s oxidation of ethylene with O2 in presence of a catalyst, in place of its synthesis by oxidation of ethanol or hydration of acelylene with H2SO4.
f) For the production of plastics, two chemicals have been proven green.
Among water issues facing the world today, land-based sources of water pollution are among the most pressing. As evident from projections by the United Nations, population demands on water resources will continue to climb. For the 4 billion to 7 billion people projected, in addition to supplies of food and water, will there be adequate goods and services? Will there be plastic bags? Will there be floors and ceilings? When this equation of population growth is carried out into the products, goods and services, and rising standard of living that is being demanded, it ties back to what the chemical community has to supply. Adequate supplies of satisfactory-quality water are essential for the natural resources and ecological systems on which all life depends. An estimated 20 percent of the world's freshwater fish and 80 percent of estuarine-dependent fish species, for example, have been pushed to the brink of extinction by contaminated water and loss of or damage to their habitat. By continuing down the path of “pollute first, clean up later,” chemistry is really not in a position to help. Chemistry must take a role in providing some alternatives. Leapfrog technology is required because when you look at population growth, the vast majority of it is going to take place in the developing world, not the developed world.
The ways in which water sources become contaminated are sometimes surprising. Photographic processing, for example, is one of the great “out-of-sight, out-of-mind” sources of water contamination. People across the world send their photographs out for processing each day, quite unaware of the major source of contamination that comes from photographic chemical developer simply dumped down drains. In the United States alone, the amount of photographic development waste adds up to about 1,200 million gallons of water containing 15 million gallons of developer and contaminants such as hydroquinone, ammonia, and silver.
DuPont has come up with a new photographic development system called DuCare™ that addresses this waste issue. With the DuCare system, hydroquinone developer is replaced with erythorbic acid, and 99 percent of the developer and fixer is recycled at a central facility. The chemicals are actually distributed in containers that once used are returned to DuPont for recycling. Thus, not only is the chemistry of the developer replaced, the way in which the photographic chemicals are distributed is as well. Overall, DuPont changed the nature of the business. Instead of just being a chemical supplier, it now provides a valuable service. DuPont came up with a way of delivering fixers and developers to stores that enables elimination of water use and contamination and is great for its bottom line. The only water involved now is what is originally put in the DuPont photographic processing system. Utilization of this system has the potential to the save about 395 million gallons of water per year in the United States alone. Other companies around the world are also working on incorporating this type of closed-loop approach into photographic development.
It is important to think of the scale of the economics being talked about here. The numbers are easy to come by in terms of the chemicals. The United States sells about $3.5 billion in this world market for chemical treatment, but a $5-billion-a-year market in chemicals for water treatment is actually very little. Although, it sounds like a big number, the one underlying it is substantially bigger. In terms of the industrial infrastructure, more than a trillion dollars is being protected from corrosion, from scaling, and from bacterial growth, which are huge economic problems.
When you talk about replacing these chemicals or about avoiding pollution, you have to have an idea of the scale that is being considered. Another Presidential Green Chemistry Challenge Award winner Ondeo Nalco also uses this closed-system approach.
Ondeo Nalco used to be a chemical supplier for water treatment, including chemicals for corrosion, scaling, and bacterial growth. It was quite a lucrative business too. In recent years, however, Ondeo Nalco has taken a very different approach to business. Similar to DuPont, Ondeo Nalco now provides more of a service to its customers rather than merely supplying chemicals. For its customers it provides a systematic analysis of facility use, substitute chemistry to decrease toxicity, and precise control of chemical use. Fundamentally, what has happened is that now Ondeo Nalco sells substantially fewer chemicals, which has reduced the amount of chemicals going out in water. At the same time its profit is high because it has provided an effective service for the purchaser.
The next example involves semiconductor fabrication. Semiconductor manufacturing is somewhat deceptive because semiconductor plants do not typically have smokestacks with pollutants billowing out. Also, the industry provides high-paying jobs and other features unlike the manufacturing jobs of the past. However, semiconductor manufacturing plants are essentially chemical factories with electronic output.
The resource intensity of semiconductor manufacturing is enormous. In a recent article (Williams, E.D.; Ayres, R.U.; Heller, M.Environ. Sci. Technol. 2002, 36(24); 5504-5510), it was found that 1.7 kg of chemicals and fuels are used to manufacture every 2-g, 32-MB DRAM chip produced. If you just consider water, 32,000 g of water are required for every 2-g chip. However, a lot of the water is recycled in plants and a lot of it is reused, but the water is deionized, which translates into fairly high energy content. There are also 45 g of chemicals used per 2-g chip.
Water is really a huge issue here. The average semiconductor fabrication plant will go through 2 million to 3 million gallons of deionized water a day. Typically the plants are located in semiarid regions of the country (e.g., Austin, TX; Albuquerque, NM; San Jose, CA; and Irvine, CA) that already struggle with water issues. However, this water use has not been much of an issue for the industry because economically the industry could afford it. For example, at its plant in Albuquerque, New Mexico, Intel has bought water rights from farmers up and down the Rio Grande in order to have a sufficient volume of water for its processing. Because of the very high-value product being made, paying such a high price for water was justified.
Then something occurred that changed this happy scenario. The industry hit a physics problem. The ratio of the width of features to their depth (aspect ratio) started to cause problems. Water with aqueous chemicals was used to clean the wafers as the chip features were produced. However, as the aspect ratio of the features increased, the high surface tension of the water inhibited it from being able to penetrate between the features. The industry then had to look for alternatives to water for cleaning.
A solution to this problem came out of Los Alamos National Laboratory. It was found that supercritical fluids, especially supercritical CO2, could be used for cleaning instead of water. This is because in the supercritical state, CO2 has no surface tension and can penetrate the small spaces with the addition of propylene carbonate, a food additive. The figure shows the improved performance of cleaning with supercritical CO2 This technology has been commercialized, and the supercritical fluid technology has won a Presidential Green Chemistry Challenge Award. Now six other companies are beginning the construction of new equipment for the semiconductor industry to bring this kind of technology to bear. Again, it was a rate-limiting problem, but one of the benefits is that 2 million to 3 million gallons of water a day are available for other uses. Thus, it is important to consider conservation of water resources, as well as reduction of contamination in the equation.
Comparison of a semiconductor component showing sidewall polymer (A) prior to cleaning, and (B) after cleaning with supercritical CO2.
A $4-billion-a-year problem for the shipping industry is marine fouling in coastal water regions. Every ship has this problem of buildup of marine organisms. Organisms on ships' surfaces increase drag and fuel costs, but cleaning them off is an expensive process, and takes a ship out of service. The typical approach to this problem has been the use of tributyltin in paint. Tributyltin kills marine organisms, but unfortunately, it also bioaccumulates and becomes toxic to larger organisms. In coastal regions, immune, reproductive, and mutagenic effects in marine organisms are now quite high. This makes less food available in coastal regions and has led to some very long term impacts.
Marine fouling a major economic and environmental issue.
Rohm and Haas looked at this problem and developed the new Sea-Nine® antifoulant, 4,5-dichloro-2-n-octyl-4- isothiazolin-3-one (DCOI). The metabolic breakdown products of DCOI are nontoxic and do not bioaccumulate. DCOI is also cost competitive with tributyltin. It thus made sense for shipowners to switch to the less toxic alternative. Adoption of the new antifoulant was also facilitated by the number of international regulations beginning to ban the use of tributyltin. Again, regulation coupled with effective chemistry tools has helped shipowners move to use of the more environmentally friendly alternative and eliminate the use of tributyltin.
At the heart of sustainable development are food and water. It would not be possible to support the current population or that of the future without being able to provide food in a sustainable way. Providing enough food and water has a lot to do with the chemical industry. The chemical revolution of the 1950s and 1960s made it possible to grow enough food to sustain the planet's population. The agricultural chemicals industry is big, with $12 billion a year in pesticides alone. That is a fairly healthy dollar figure, but it is not healthy in terms of persistence and bioaccumulation. Really, the environmental movement began with Rachael Carson in the 1950s identifying the pathways of bioaccumulation of dichlorodiphenyltrichloroethane (DDT) in organisms.
Chemistry is going to have a critical role in a sustainable future, but what kind of chemistry will it be? In terms of herbicides and pesticides, they are not a problem for the most part when applied in correct doses in a scientifically responsible way. However, around the world, these chemicals are often mishandled, and proper safety procedures are not followed. Even here in the United States the typical person applying herbicides and pesticides to a lawn does not always read or follow the safety instructions provided.
The issue is how to avoid contamination of the environment in the first place. Over the last few years a number of Presidential Green Chemistry Challenge Awards have gone for agricultural applications and pesticide applications. There are even more examples such as the area of roach protection, ant protection, and other household uses. Companies are going to very different systems of alternative pesticides, including the biomimetic approach. Instead of using a broad-scale neurotoxin to go after a species, more specific targets are being sought.
For example, Dow and Rohm and Haas separately have developed biomimetic pesticides that mimic the hormonal input that causes molting. Insects do not eat when they molt. If they are forced to molt early, they starve to death. These are endocrine hormones that essentially dissipate very quickly in the environment and are also effective in small doses. Thus, instead of having to use large quantities across fields, very small quantities can be used.
Another approach that is somewhat more controversial is the use of genetic engineering. What Eden Biosciences did is essentially study the plant biology. Plants have what can be thought of as the equivalent to an immune system that, when challenged with a disease or by insect infestation, leads to a protein cascade while the plant tries to fight it off. These proteins were identified, and now Eden is engineering them. When they are applied to the plants, increased growth and increased resistance to both disease and drought are obtained.
There are two or three advantages presented by these examples from the green chemistry community. One is that smaller doses are being used, and this means increased worker safety. The UN Food and Agriculture Organization has estimated that 10,000 agricultural workers die annually from pesticide poisoning. There is thus a very good reason to put things on the market that are less harmful, not only to the environment, but to the people who are working in the field. Another great advantage of the examples presented is the decreased water use, not only decreased water contamination.
Donlar Corporation won another award for its poly-aspartic acid (PAA), which it uses in disposable diapers and other applications that require absorbents. Now it has also developed an agricultural application of PAA as an absorbent around the roots of plants that creates a sink for water and chemicals. It draws water from the surrounding area into the plant, which means less water use.
Environmental chemistry is the study of the natural environment and the pollutants that plague it. Green chemistry is also called sustainable chemistry and aims to minimize or eliminate the use and generation of hazardous substances.
Let us elaborate on the fundamental concept of sustainability to get a clearer picture.
Chemistry has improved our quality of life and made thousands of products possible. Unfortunately, this achievement has come at a price: our collective human health and the global environment are threatened. Our bodies are contaminated with a large number of synthetic industrial chemicals, many of which are known to be toxic and carcinogenic while others remain untested for their health effects. Many chemicals work their way up the food chain and circulate round the globe; pesticides used in the tropics are commonly found in the Arctic; flame retardants used in furniture and electronics are now commonly found in marine mammals. Yet as cancer rates rise and evidence increases about the link between certain chemicals and birth defects and learning disabilities our regulatory system has been unable to make chemical producers provide full testing information or promote inherently safer chemicals. They can destroy natural resources and especially the means of livelihood for future generations. In addition, many feedstocks for the production of chemicals are based on petroleum, which is not a renewable resource.
The key question to address is: what alternatives can be developed and used? In addition, we must ensure that future generations can also use these new alternatives. "Sustainability" is a concept that is used to distinguish methods and processes that can ensure the long-term productivity of the environment, so that we may satisfy the need of the present generations without compromising the ability of the future generations to satisfy theirs.
 |
| ILLUSTRATING THE SCOPE OF SUSTAINABILITY |
One striking example of a sustainable society can be seen in this documentary: Satoyama: Japan's Secret Water Garden II
Green chemistry applies to organic chemistry, inorganic chemistry, biochemistry, analytical chemistry, and even physical chemistry. The concept of invention and design is the soul of this discipline.
The term Green Chemistry was coined in 1991 by Paul Anastas of the U.S. Environmental Protection Agency so let's have a look at the list the Green chemical principles formulated by him :
1. Waste prevention instead of remediation - It is better to prevent waste than to treat or clean up waste after it is formed. Along the lines of the age old saying, 'Prevention is better than cure'.
2. Atom economy or efficiency - concept that evaluates the efficiency of a chemical transformation.
% Atom Economy = No. of atoms incorporated x 100.
No. of atoms in the reactants
Choosing transformations that incorporate most of the starting materials into the product are more efficient and minimize waste. Diels–Alder reaction (between a conjugated diene and a substituted alkene, to form a substituted cyclohexene system) is 100% atom economy reaction as all the atoms of the reactants are incorporated in the cycloadduct.
 |
| DIELS-ALDER REACTION |
3. Use of less hazardous and toxic chemicals - This principle focuses on choosing reagents and synthetic methodologies that pose the least risk and generate only benign by-products that possess little or no threat to human health and environment.
For example, in the manufacture of polystyrene foam sheet packing material chlorofluorocarbons (which contribute to O3 depletion, global warming and ground level smog) have now been replaced by CO2 as the blooming agent.
4. Safer products by design - A pertinent example of smarter production is metathesis which was developed by Grubbs, Schrock and Chauvin. It is a reaction in which double bonds are broken and made between carbon atoms in ways that cause atom groups to change places,with the help of special catalyst molecules. It is used in the development of pharmaceuticals and advanced plastic materials, and is a great step forward for green chemistry.
To know more about this Nobel Prize winning contribution, click on : http://en.wikipedia.org/wiki/Olefin_metathesis
Note: Pharmaceutical products often consist of chiral molecules, and the difference between the two forms can be a matter of life and death.
a) Ionic liquids are liquids at RT and below. They are non volatile and have no vapour pressure. They can serve as optimal replacements for volatile organic traditionally used industrial solvents. The reactions in ionic liquids need no special apparatus and methodologies, and they can be recycled.
b) Supercritical CO2 fluid is now becoming an important commercial and industrial solvent for chemical separation because of its low toxicity and non-inflammability.
c) Supercritical water: Many organic compounds become soluble in water when it becomes supercritical at 374oC and 218atm. Hence, it is used as a clean and cheap solvent.
d) Reactions in aqueous phase: Replacement of organic solvents with eco-friendly water has found success with many reactions,some of which may occur at higher rates because of its high polarity. They include oxidations, reductions, epoxidations, polymerizations (with or without catalysts) and many named reactions.
e) Reactions in solid phase: Large number of reactions occuring in solid state, without the solvent, utilize the surfaces or interiors of clays, zeolites, silica, and alumina.These reactions are simple to operate, economical and solvent-related pollution is avoided.
 |
| STRUCTURE OF TWO SILICATES |
a) Microwave irradiation: Reactions with microwave sources have been carried out in a solid support like clay, silica gel, etc., eliminating or minimizing the use of solvents. The reactions take place at a faster rate than thermal heating. For example Beckmann rearrangement of oximes in the solid state with microwave irradiation gave quantitative yields of the products without the use of acid catalysts.
 |
| BECKMANN REARRANGEMENT OF OXIMES |
b) Sonochemistry (Ultrasound energy): Reactions using ultra- sound energy are carried out at RT with excellent yields. For example, Ullmann’s coupling which takes place at higher temperature giving low yields by conventional method, gives increased yields at low temperature and in short duration with ultra sound energy.
 |
| ULLMANN'S COUPLING |
8. Shorter syntheses (avoid derivatization) - 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 more waste. Instead more selective and better alternative synthetic sequences that eliminate the need for functional group protection should be adopted.
9. Catalytic rather than stoichiometric reagents - Catalysts are used in small amounts and can carry out a single reaction many times and so are preferable to stoichiometric reagents, which are used in excess and work only once. They can enhance the selectivity of a reaction, reduce the temperature of a transformation, reduce reagent based waste and potentially avoid unwanted side reactions leading to a clean technology. Apart from heavy metal catalysts softer catalysts like zeolites, phase transfer catalysts, (e.g., crown ethers), are finding increasing industrial applications.
10. Design products to undergo degradation in the environment - They should not accumulate and persist in the environment but break down into innocuous hazardless substances at the end of their function.
11. Inherently safer processes - Design chemicals and their forms (solid, liquid, or gas) to minimize the chemical accidents including explosions, fires and releases to the environment.
Example, manufacture of gold atom nanoparticles used diborane (highly toxic and bursts into flame near room temperature) and cancer-causing benzene. Now, diborane has been replaced by environmentally benign NaBH4 which also eliminates the use of benzene.
Nanoscience and nanotechnology is another important contribution to green chemistry. Nanotechnology provides huge savings in materials by development of microscopic and submicroscopic electronic and mechanical devices.
12. Analytical methodologies for pollution prevention - Instances elucidate best.
a) The most polluting reaction in industry is oxidation. Implementation of green chemistry has led to the use of alternative less polluting reagents viz. metal ion contamination is minimized by using molecular O2 as the primary oxidant and use of extremely high oxidation state transition metal complexes.
b) Conventional methylation reactions employing toxic alkyl halides or methylsulfate leading to environmental hazard are replaced by dimethyl carbonate with no deposit of inorganic salts e.g., methylation of arylacetonitriles in presence of K2CO3 to 2- arylpropionitriles (> 99%).
(Click here to download a pdf file about the chemistry of dimethyl carbonate)
c) In the synthesis of polycarbonates use of phosgene and methylene chloride has been replaced by diphenyl carbonate.
d) Use of CO2 as a reaction medium for asymmetric catalytic reductions particularly hydrogenation and H2 transfer reactions.
e) A convenient green synthesis of acetaldehyde is by Wacker-chemie’s oxidation of ethylene with O2 in presence of a catalyst, in place of its synthesis by oxidation of ethanol or hydration of acelylene with H2SO4.
 |
| WACKER-CHEMIE'S OXIDATION OF ALKENES |
f) For the production of plastics, two chemicals have been proven green.
INNOVATION IN THE FIELD
BIOPESTICIDES:
INNOVATION IN THE FIELD
BIOPESTICIDES:
BIOPESTICIDES:
Serious questions remain about the safety of biopesticide products from both a human and ecosystem health standpoint. Current regulations do not go nearly far enough in evaluating systemic broader impacts of biopesticides. By definition, Green Chemistry is about continuous improvements aimed at reducing or eliminating hazard. Fully defining hazard is difficult. Even products hailed by Green Chemists and regulators alike as safer for human health may turn out to have unforeseen negative environmental health impacts. See for example, Spinosad, a green chemistry award winning biopesticide, which while significantly safer for humans than other pesticides but is toxic to bees.
We must encourage pest management solutions and regulations to continuously evolve. We must also ensure that multi-disciplinary teams, including Green Chemists, environmental health specialists and other scientists, approach these innovations holistically.
An Alternative to Methyl Bromide: “Pasteuria” for Nematode Control
Plant parasitic nematodes are one of agriculture’s largest challenges. These microscopic worms burrow into the soil and attack plant roots causing damage to crops, causing an estimated $100 billion in worldwide crop damage annually. They have traditionally been controlled by fumigants, notably the problematic chemical methyl bromide. As fumigants are being phased due to negative human and environmental health effects, alternatives such as biological controls are being investigated.
Microbial pesticides have specific advantages over fumigants in the control of nematodes. Nematodes can burrow deep into the soil during fumigant applications to avoid contact. They can then ascend to the level of the plant roots after crops have emerged, at which point fumigants cannot be reapplied due to their toxicity and potential to damage crops. In contrast, many microbial pesticides can be applied to the post-emergent crops for protection throughout the plant life cycle. However, many microbial pesticides depend on the nematode consuming the microbe. This can present a challenge because plant pathogenic nematodes are generally herbivores.
More than 50 years ago, academic and USDA researchers discovered a genus of bacteria called Pasteuria to be a promising alternative for the control of nematodes. A particular advantage of Pasteuria over other biological controls is that it does not need to be eaten by the nematode to be effective. The Pasteuria spores are applied to the soil, and as a nematode passes, they attach to the nematode’s outer cuticle. The spores germinate and enter the nematode’s body causing death, spreading new spores into the soil. Each strain of the bacteria is specific to a particular species of nematode.
The primary technical challenge for commercialization of Pasteuria was development of an economically viable large-scale manufacturing process. The initial process developed in the laboratory involved growing live nematodes as hosts, growing the bacteria inside the hosts (in vivo), and extracting the spores to formulate the product. This process was too costly to scale up and a technological breakthrough was needed. The technical challenge was recently overcome by finding a way to grow the bacteria outside of a living host (in vitro). A new-patented process allows rapid and effective growth of multiple strains of Pasteuria penetrans in traditional commercial fermentation tanks using easily available growth media (Pasteuria, 2008). This technological advance significantly decreased the cost of production, making the product economically viable.
Mating Disruption as a Pest Management Tool In California’s Wine Industry
Within the last decade the vine mealybug (Planococcus ficus) invaded and spread through California from Mexico, causing significant damage to valuable vineyards. The initial response was to focus on eradication. A pheromone was identified for detection and monitoring of the invasive species. Jocelyn Millar and his lab at University of California at Riverside successfully conducted applied research to synthesize the pheromone molecule and develop and test its use in pheromone-baited monitoring traps. However, as the vine mealybug became established in many of California’s grape growing regions, the focus shifted from eradication to control.
Due to its effectiveness in traps, developing the pheromone to control vine mealybug populations using mating disruption was pursued. The key goal of the research was to identify less-toxic insecticides that may be effective alternatives to organophosphates. Two companies got involved in the commercialization of large scale mating disruption products. Kuraray developed the synthesis route and process for large-scale production of the active ingredient, and Suterra developed the pesticide product including selection of inert ingredients, design of the applicator, and product testing and registration. Some of the field-testing was coordinated and conducted in collaboration with Kent Daane and his team at the University of California Berkeley Extension.
The white waxy exterior of the vine mealybug combined with its habit of hiding under the bark can make it particularly challenging to control. Most pesticides require direct contact with the mealybug, and will not be effective against those under the bark. Many of the “softer” insecticides are not able to penetrate the waxy exterior; some insecticides such as soap even slide off the bug. However, pheromones are volatile molecules dispersed through the air and sensed by the insect without requiring penetration (analogous to perfumes being sensed by humans).
Through field-testing, researchers also discovered unexpected benefits. One was that application of the pheromone seemed to attract higher populations of natural vine mealybug predators to the application area. The higher level of pheromones presumably fooled the parasitoid predators into believing there were more vine mealybugs present. The pheromone-filled air attracted the natural predators to the fields.
A second benefit of the pheromones use over conventional broad-spectrum pesticides was that the ecological balance and natural predator populations where preserved. This specificity can prevent the need for additional pesticides later in the season to control secondary pest population. Secondary pest populations often surge later in the season when broad-spectrum pesticides are used because the pesticides kill natural predators of the primary pest.
Vine mealybug pheromones are often integrated into pest management systems, particularly for the first several years when pest pressure is high. They can be used stand-alone after several years if pest populations are managed at a low level. When used in systems, they are often combined with neonicotinoids, insect growth regulators, or other biopesticides – some of these other methods have raised concerns about intended impacts on non-target organisms such as bees.
Growers need transparent and comprehensive information to make informed choices between vine mealybug management options. The use of the vine mealybug pheromone is not a one for one replacement for organophosphates. Pheromone use has unique benefits and limitations that must be understood to assess the trade-offs. In addition, new skill sets are required of growers to properly identify and monitor both the pest and its life cycle, as well as to evaluate other tools used in comprehensive insect management systems.
This example demonstrates the complexity of both developing and using biopesticides, from the collaborative development process often required to bring biopesticides to the market, to the need for transparency and education to allow growers to make informed choices, to the niche nature of pheromones and the challenges in designing IPM systems.
Some organizations that work to promote sustainable agriculture and biopesticide issues.
- Biopesticide Industry Alliance
- Environmental Protection Agency – Biopesticide Information
- Institute for Agriculture and Trade Policy
- The Organic Center
- Pesticide Action Network North America
ADDRESSING GLOBAL CHALLENGES
Among water issues facing the world today, land-based sources of water pollution are among the most pressing. As evident from projections by the United Nations, population demands on water resources will continue to climb. For the 4 billion to 7 billion people projected, in addition to supplies of food and water, will there be adequate goods and services? Will there be plastic bags? Will there be floors and ceilings? When this equation of population growth is carried out into the products, goods and services, and rising standard of living that is being demanded, it ties back to what the chemical community has to supply. Adequate supplies of satisfactory-quality water are essential for the natural resources and ecological systems on which all life depends. An estimated 20 percent of the world's freshwater fish and 80 percent of estuarine-dependent fish species, for example, have been pushed to the brink of extinction by contaminated water and loss of or damage to their habitat. By continuing down the path of “pollute first, clean up later,” chemistry is really not in a position to help. Chemistry must take a role in providing some alternatives. Leapfrog technology is required because when you look at population growth, the vast majority of it is going to take place in the developing world, not the developed world.
Photographic Chemicals—A Closed-Loop Approach
DuPont has come up with a new photographic development system called DuCare™ that addresses this waste issue. With the DuCare system, hydroquinone developer is replaced with erythorbic acid, and 99 percent of the developer and fixer is recycled at a central facility. The chemicals are actually distributed in containers that once used are returned to DuPont for recycling. Thus, not only is the chemistry of the developer replaced, the way in which the photographic chemicals are distributed is as well. Overall, DuPont changed the nature of the business. Instead of just being a chemical supplier, it now provides a valuable service. DuPont came up with a way of delivering fixers and developers to stores that enables elimination of water use and contamination and is great for its bottom line. The only water involved now is what is originally put in the DuPont photographic processing system. Utilization of this system has the potential to the save about 395 million gallons of water per year in the United States alone. Other companies around the world are also working on incorporating this type of closed-loop approach into photographic development.
Industrial Waste Treatment
When you talk about replacing these chemicals or about avoiding pollution, you have to have an idea of the scale that is being considered. Another Presidential Green Chemistry Challenge Award winner Ondeo Nalco also uses this closed-system approach.
Ondeo Nalco used to be a chemical supplier for water treatment, including chemicals for corrosion, scaling, and bacterial growth. It was quite a lucrative business too. In recent years, however, Ondeo Nalco has taken a very different approach to business. Similar to DuPont, Ondeo Nalco now provides more of a service to its customers rather than merely supplying chemicals. For its customers it provides a systematic analysis of facility use, substitute chemistry to decrease toxicity, and precise control of chemical use. Fundamentally, what has happened is that now Ondeo Nalco sells substantially fewer chemicals, which has reduced the amount of chemicals going out in water. At the same time its profit is high because it has provided an effective service for the purchaser.
Lithographic Technologies—Water Conservation
The resource intensity of semiconductor manufacturing is enormous. In a recent article (Williams, E.D.; Ayres, R.U.; Heller, M.Environ. Sci. Technol. 2002, 36(24); 5504-5510), it was found that 1.7 kg of chemicals and fuels are used to manufacture every 2-g, 32-MB DRAM chip produced. If you just consider water, 32,000 g of water are required for every 2-g chip. However, a lot of the water is recycled in plants and a lot of it is reused, but the water is deionized, which translates into fairly high energy content. There are also 45 g of chemicals used per 2-g chip.
Water is really a huge issue here. The average semiconductor fabrication plant will go through 2 million to 3 million gallons of deionized water a day. Typically the plants are located in semiarid regions of the country (e.g., Austin, TX; Albuquerque, NM; San Jose, CA; and Irvine, CA) that already struggle with water issues. However, this water use has not been much of an issue for the industry because economically the industry could afford it. For example, at its plant in Albuquerque, New Mexico, Intel has bought water rights from farmers up and down the Rio Grande in order to have a sufficient volume of water for its processing. Because of the very high-value product being made, paying such a high price for water was justified.
Then something occurred that changed this happy scenario. The industry hit a physics problem. The ratio of the width of features to their depth (aspect ratio) started to cause problems. Water with aqueous chemicals was used to clean the wafers as the chip features were produced. However, as the aspect ratio of the features increased, the high surface tension of the water inhibited it from being able to penetrate between the features. The industry then had to look for alternatives to water for cleaning.
A solution to this problem came out of Los Alamos National Laboratory. It was found that supercritical fluids, especially supercritical CO2, could be used for cleaning instead of water. This is because in the supercritical state, CO2 has no surface tension and can penetrate the small spaces with the addition of propylene carbonate, a food additive. The figure shows the improved performance of cleaning with supercritical CO2 This technology has been commercialized, and the supercritical fluid technology has won a Presidential Green Chemistry Challenge Award. Now six other companies are beginning the construction of new equipment for the semiconductor industry to bring this kind of technology to bear. Again, it was a rate-limiting problem, but one of the benefits is that 2 million to 3 million gallons of water a day are available for other uses. Thus, it is important to consider conservation of water resources, as well as reduction of contamination in the equation.
Comparison of a semiconductor component showing sidewall polymer (A) prior to cleaning, and (B) after cleaning with supercritical CO2.
Marine Environment—Anitfoulants
Marine fouling a major economic and environmental issue.
Rohm and Haas looked at this problem and developed the new Sea-Nine® antifoulant, 4,5-dichloro-2-n-octyl-4- isothiazolin-3-one (DCOI). The metabolic breakdown products of DCOI are nontoxic and do not bioaccumulate. DCOI is also cost competitive with tributyltin. It thus made sense for shipowners to switch to the less toxic alternative. Adoption of the new antifoulant was also facilitated by the number of international regulations beginning to ban the use of tributyltin. Again, regulation coupled with effective chemistry tools has helped shipowners move to use of the more environmentally friendly alternative and eliminate the use of tributyltin.
Agriculture
Chemistry is going to have a critical role in a sustainable future, but what kind of chemistry will it be? In terms of herbicides and pesticides, they are not a problem for the most part when applied in correct doses in a scientifically responsible way. However, around the world, these chemicals are often mishandled, and proper safety procedures are not followed. Even here in the United States the typical person applying herbicides and pesticides to a lawn does not always read or follow the safety instructions provided.
The issue is how to avoid contamination of the environment in the first place. Over the last few years a number of Presidential Green Chemistry Challenge Awards have gone for agricultural applications and pesticide applications. There are even more examples such as the area of roach protection, ant protection, and other household uses. Companies are going to very different systems of alternative pesticides, including the biomimetic approach. Instead of using a broad-scale neurotoxin to go after a species, more specific targets are being sought.
For example, Dow and Rohm and Haas separately have developed biomimetic pesticides that mimic the hormonal input that causes molting. Insects do not eat when they molt. If they are forced to molt early, they starve to death. These are endocrine hormones that essentially dissipate very quickly in the environment and are also effective in small doses. Thus, instead of having to use large quantities across fields, very small quantities can be used.
Another approach that is somewhat more controversial is the use of genetic engineering. What Eden Biosciences did is essentially study the plant biology. Plants have what can be thought of as the equivalent to an immune system that, when challenged with a disease or by insect infestation, leads to a protein cascade while the plant tries to fight it off. These proteins were identified, and now Eden is engineering them. When they are applied to the plants, increased growth and increased resistance to both disease and drought are obtained.
There are two or three advantages presented by these examples from the green chemistry community. One is that smaller doses are being used, and this means increased worker safety. The UN Food and Agriculture Organization has estimated that 10,000 agricultural workers die annually from pesticide poisoning. There is thus a very good reason to put things on the market that are less harmful, not only to the environment, but to the people who are working in the field. Another great advantage of the examples presented is the decreased water use, not only decreased water contamination.
Donlar Corporation won another award for its poly-aspartic acid (PAA), which it uses in disposable diapers and other applications that require absorbents. Now it has also developed an agricultural application of PAA as an absorbent around the roots of plants that creates a sink for water and chemicals. It draws water from the surrounding area into the plant, which means less water use.
