Green Chemistry

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Green Chemistry (1) The meaning of green chemistry. Green Chemistry is also known as Environmentally Benign Chemistry, Environmentally Friendly Chemistry, or Clean Chemistry. In the early 1990s, chemists proposed the concept of \"green chemistry\", which differs from the traditional approach of \"pollution control\"; it requires that any chemical-related activity – including the use of chemical raw materials, chemical and chemical engineering processes, as well as the final products – be friendly to both human health and the environment. The ideal of green chemistry is to stop using toxic and harmful substances and to avoid generating waste. From a scientific perspective, green chemistry represents an update to the fundamental aspects of chemical science ； From an environmental perspective, it emphasizes eliminating pollution at its source ； From an economic perspective, it advocates for the rational use of resources and energy to reduce production costs, which is in line with the requirements of sustainable development. Basic principles of green chemistry: ① Preventing pollution from being generated is better than treating pollution that has already been generated ； ②Atom economy (the synthetic method designed should convert as much of the materials used in the reaction process as possible into the final product) ； ③Wherever possible, synthetic routes that are low-toxic or non-toxic to humans and the environment should be employed ； ④The designed chemicals should maintain their efficacy while reducing their toxicity ； ⑤The use of auxiliary substances (such as solvents, separation reagents, etc.) should be avoided as much as possible; if they are used, they must be non-toxic ； ⑥The impact of energy consumption on the environment and the economy should be taken into account, and energy should be used as little as possible (under normal temperature and pressure conditions) ； ⑦As long as it is technically and economically feasible, the raw materials should be renewable rather than nearing exhaustion ； ⑧Try to avoid unnecessary derivative steps (blocking groups, protection and deprotection, etc.) ； ⑨Catalysts (with the best possible selectivity) are superior to stoichiometric reagents ； ⑩After fulfilling their purpose, chemical products should be able to degrade into harmless substances, without remaining in the environment ； Analytical methods should be further developed to enable real-time online tracking and control of harmful substances before they are generated ； During the chemical conversion process, the substances chosen and their form are selected in such a way as to minimize the likelihood of chemical accidents (including leaks, explosions, fires, etc.). The aforementioned 12 principles of green chemistry reflect the various research efforts carried out in this field over recent years, and they also indicate the direction for the future development of green chemistry; they are now gradually being accepted by the international chemical community. The concept of \"atom economy\" in chemical reactions is one of the core aspects of green chemistry. It was first proposed by Professor B.M. Trost at Stanford University in the United States. In response to the traditional practice of evaluating the feasibility of chemical processes solely based on economic considerations, he argued that a new standard should be used for such assessments – selectivity and atom economy. Atom economy takes into account how many atoms from the reactants end up in the product. This standard requires not only the maximum conservation of non-renewable resources but also the minimization of waste generation. An ideal atom-economical reaction is one in which 100% of the atoms in the reactant molecules are converted into products, with no by-products or waste generated, achieving \"zero emission\" of waste. “The concept of “atomic economy” is also widely recognized today. B.M. Trost received the academic award for the 1998 U.S. President’s Green Chemistry Challenge Award. (2) Green chemistry in action: As the direction and foundation for the future development of the chemical industry, green chemistry is attracting increasing attention from governments, enterprises, and academia around the world. For example, in 1995, the “President’s Green Chemistry Challenge Award” was established in the United States to honor individuals, groups, or organizations that have achieved outstanding results in the creative research, development, and application of the fundamental principles of green chemistry. It includes 5 awards in total: the Academic Award, the Small and Medium Enterprise Award, the New Synthesis Route Award, the New Process Award, and the Safe Chemical Design Award. The book \"Theory and Practice of Green Chemistry\" published in 1998 is a classic work on green chemistry, which details the definition, principles, evaluation methods, and development trends of green chemistry. The international journal ‘Green Chemistry’, sponsored by the Royal Society of Chemistry, was founded in 1999. Its contents include various research findings, reviews, and other information on clean chemical production technologies, as well as academic research activities worldwide aimed at reducing environmental impacts through the use or processing of chemicals. By tracing the history of some American Green Chemistry Awards, we can identify the main achievements and trends in current research on green chemistry processes and technologies: ① Development of \"atom-economical\" reactions. In recent years, the development of atom-economical reactions has become one of the key focuses in green chemistry research. For example, propylene oxide is an important raw material for producing polyurethane plastics. Traditionally, the chlorohydrin method involving a two-step reaction has been used; this method not only relies on chlorine gas, which can be hazardous, but also generates large amounts of calcium chloride-containing wastewater that pollutes the environment. Both domestically and internationally, new atom-economical methods for producing propylene oxide through the catalytic oxidation of propylene are being developed. For another example, EniChem uses titanium-silica molecular sieve catalysts to react ** with ammonia and hydrogen peroxide, thereby directly synthesizing ** oxime. Even for atom-economical reactions that are already in industrial use, further research and improvement are still needed from the perspectives of environmental protection and techno-economics. To achieve high atom economy in reactions, it is necessary to employ methods such as developing new reaction pathways and replacing stoichiometric reactions with catalytic reactions; the work of BCH Company, the winner of the 1997 New Synthesis Route Award, is a good example of this. The company has developed a new process for synthesizing ibuprofen (an extensively used non-steroidal drug with analgesic and anti-inflammatory properties). The traditional production method involves 6 stoichiometric chemical reactions, resulting in an effective atom utilization rate of less than 40%. The new process utilizes 3 catalytic reactions, achieving an effective atom utilization rate of 80%; when the recovery and reuse of the by-product acetic acid is taken into account, the atom utilization rate reaches 99%. ②Use of non-toxic and harmless raw materials: For the sake of human health and environmental safety, it is necessary to use non-toxic and harmless raw materials to produce the chemical products required, in place of toxic and harmful ones. For example, Monsanto Company used non-toxic and harmless diethanolamine as a raw material and developed a catalytic dehydrogenation process to produce sodium amino diacetate safely, replacing the previous two-step synthesis route that relied on ammonia, formaldehyde, and hydrocyanic acid. For this achievement, it received the New Synthesis Route Award at the 1996 U.S. President’s Green Chemistry Challenge. In addition, new synthesis routes for producing methyl methacrylate from isobutylene have been developed abroad, replacing the propiononitrile method that uses propiononitrile and hydrogen cyanide as raw materials. ③Non-toxic and harmless catalysts are used. Currently, in the alkylation of hydrocarbons, liquid acidic catalysts such as hydrofluoric acid, sulfuric acid, and aluminum trichloride are generally employed. The common drawbacks of these catalysts include severe corrosion of equipment, harm to human health, generation of waste residues, and environmental pollution. Currently, both domestically and internationally, solid acid catalysts for alkylation are being actively developed from new catalytic materials such as molecular sieves, heteropoly acids, and superacids. For example, the alkylation of isobutane with butylene is an important process in the petroleum refining industry for producing high-octane components; currently, hydrofluoric acid or sulfuric acid is used as a catalyst. Some companies have developed new processes for isobutane/butylene alkylation using supported sulfonate/SiO2 catalysts and solid acid catalysts. ④By using non-toxic and harmless solvents and additives, many pollution problems associated with chemical production stem not only from raw materials and products but also from the substances used in the manufacturing process, with solvents used in reaction media, formulations, and separation being the most common ones. The solvents widely used today are volatile organic compounds; some of them can damage the ozone layer while others pose risks to human health. Therefore, it is necessary to restrict the use of such solvents. Using non-toxic and harmless solvents to replace volatile organic compound solvents has become an important research direction in green chemistry. Currently, the most active research project is the development of supercritical fluids, particularly supercritical carbon dioxide, as solvents. The 1997 academic award was given to Professor J.M. DeSimone of North Carolina University for his development of a class of surfactants that are carbon dioxide-affinity molecules, capable of exhibiting amphoteric properties toward both carbon dioxide and solutes; this enables carbon dioxide to be used extensively as a solvent in place of conventional halogen-containing organic solvents. In addition to the use of supercritical solvents, research has also been conducted on using water or near-critical water as solvents, as well as on interfacial reactions between organic solvents and aqueous phases. Organic synthesis reactions using water as a medium represent an important part of environmentally friendly synthetic processes. Organic reactions in aqueous phases are simple to carry out and safe; they do not pose the problems associated with flammable or explosive organic solvents. Moreover, water is an abundant resource, its cost is low, and it causes no pollution. Although water is a potentially environmentally friendly reaction medium, using water as such a medium inevitably raises many new issues, such as the hydrophobicity of organic substrates in water, the stability of reaction substrates and reagents in water, the influence of the numerous hydrogen bonds present in water on the reactions, and the possibility that these factors could alter the reaction mechanism. As a result, research on aqueous-phase organic synthesis reactions has become an active area of study in organic synthesis chemistry. The academic award of the 2001 U.S. \"President’s Green Chemistry Challenge Award\" was given to Professor Li Chaojun, a Chinese scholar based in the United States, which also indicates that research on organic reactions in aqueous media is receiving increasing attention. Professor Li Chaojun has achieved a series of remarkable innovative results in the design and development of transition metal-mediated and catalytic organic reactions in water and air. Aquatic-phase catalytic reactions hold broad application prospects in areas such as drug synthesis, the synthesis of fine chemicals, and polymer synthesis, opening up new fields for organic synthesis reactions that traditionally could only be carried out in inert gases and organic solvents. ⑤Synthesizing chemicals using renewable resources: Replacing the currently widely used non-renewable petroleum with renewable biomass (biomass, biological raw materials) is a significant and long-term development direction. The technology for converting biomass into animal feed, industrial chemicals, and fuel is a highly active area of research. Professor M. Holtzapple in the United States has achieved outstanding accomplishments in this field, winning the academic award of the 1996 U.S. \"President’s Green Chemistry Challenge Award\". Although there is no clear conclusion as to whether certain biocatalysts can cause pollution, in general, biotransformation meets the requirements of green chemistry well, featuring high efficiency, high selectivity, and clean production. The reaction products are simple and easy to separate and purify; it avoids the use of precious metals and organic solvents, has low energy consumption, and enables the synthesis of compounds that are difficult to produce using chemical methods. The academic award in the 1996 U.S. President’s Green Chemistry Challenge was given to Professor M. Holtzapple of Texas A&M University for developing a series of technologies to convert waste biomass into animal feed, industrial chemicals, and fuel. Renowned chemist Chi-Huey Wong received the 2000 U.S. President’s Green Chemistry Challenge Award for his remarkable innovative achievements in enzyme-catalyzed reactions. ⑥Environmentally friendly products: As environmental protection becomes a consensus in modern society, there is an increasing demand for such products. The standards set by various countries also raise the quality requirements for products in this regard. For example, in the case of motor vehicle fuel, as environmental protection requirements become increasingly stringent, in order to reduce air pollution such as ozone depletion and photochemical smog caused by carbon monoxide and hydrocarbons in vehicle exhausts, the United States has **gradually promoted the use of gasoline with new formulations. These formulations require restrictions on the vapor pressure and benzene content of gasoline, and there are also plans to gradually limit the levels of aromatics and olefins; in addition, oxygenates such as methyl tert-butyl ether and methyl tert-amyl ether are required to be added to gasoline. The increased quality requirements for this new type of gasoline formula have driven the development of related refining technologies. For another example, in 1996, the Green Chemistry Challenge Award of the U.S. President was given to Rohm Haas Company for its development of an environmentally friendly antifouling agent for marine use, designed to prevent the formation of fouling on the bottoms of ships at sea. The Small and Medium Enterprise Award was given to Donlar Company for developing two efficient processes for producing thermopolyaspartic acid, a biodegradable product that serves as a substitute for acrylic acid. (3) Green chemistry activities in our country: Activities related to green chemistry are also becoming increasingly active in our country. In 1995, the Chemistry Department of the Chinese Academy of Sciences organized an academician consultation activity titled \"Green Chemistry and Technology – Pathways to Promoting Sustainable Development in the Chemical Industry.\" Extensive research was conducted on the current status and development trends of green chemistry both domestically and internationally, and based on the domestic situation, seven recommendations were put forward for advancing green chemistry and technology as well as eliminating and reducing sources of environmental pollution. In 1997, the major basic research project under the “Ninth Five-Year Plan” titled “Environment-Friendly Catalytic Chemistry and Chemical Reaction Engineering in the Petrochemical Industry,” jointly funded by the National Natural Science Foundation of China and Sinopec Corporation, was officially launched. This project covered some key processes in China’s petrochemical industry, and it involved three levels of research: fundamental basic research, preliminary exploration of technical feasibility, and in-depth investigation into both technical feasibility and economic viability. It focused on the exploration of new technologies such as the use of non-toxic and harmless raw materials, catalysts, and “atom-economical” reactions, in order to lay the foundation for addressing the environmental issues associated with existing production processes. In the same year, the **Development Plan for Key Basic Research** was formulated to implement the strategy of developing the country through science and education, to achieve the ambitious goals for China’s economic, scientific, and social development by 2010 and by the middle of the 21st century, to ensure a continuous improvement in the country’s capacity for scientific and technological development, and to meet the challenges of the new century. This plan also identified basic research projects in green chemistry as one of the important areas for support. In addition, some colleges and universities have also established specialized research institutions for green chemistry. This post was last edited by johncom on 2009-4-1 08:51]