Challenges facing chemistry 1. 1 The image of chemistry is being buried by the great success of its interdisciplinary. Chemistry is a central science, which is closely related to eight sunrise sciences such as life and materials, and has produced many important interdisciplinary subjects. However, the image of chemistry as a central discipline has been buried by its great achievements in interdisciplinary subjects. Chemistry is an important central science, but it has not been paid attention to. Instead, it is regarded as a bridesmaid science by the society. 1.2 chemistry is being troubled by various environmental pollution problems. While the development of chemistry constantly promotes human progress, it objectively makes environmental pollution possible, but it is human factors that play a decisive role, and ultimately it depends on human understanding to solve this problem. Some famous environmental events are mostly related to chemistry, such as ozone hole, white pollution, acid rain and water eutrophication. On the other hand, it is obviously unfair to attribute all environmental problems to chemical reasons, such as the sharp decline of forests, sandstorms and coal burning. Of course, this is related to the fact that chemistry has not established its own brand. In the earliest chemical process, the treatment of waste gas and waste residue was not considered at all, so many chemical processes will bring environmental pollution. Now, some people regard chemistry and chemical industry as pollution sources. People began to hate chemistry, and then they had an inexplicable fear of chemistry. As a result, all foods containing "artificial additives" are unpopular, and some cosmetic manufacturers have repeatedly stressed that this product does not contain any "chemicals". In fact, these are all prejudices against chemistry, but it is chemists who monitor, analyze and manage the environment. Green chemistry is an inevitable science to meet the challenge. We should not only know and transform the world, but also protect it. So is chemistry. In order to meet the challenges faced by chemistry, it is urgent to advocate green chemistry. 2. 1 The concept of green chemistry Green chemistry, also known as environment-friendly chemistry, environment-friendly chemistry or clean chemistry, refers to the chemical reaction and process based on the basic principle of "atomic economy", that is, in the chemical reaction to obtain new substances, every raw material atom involved in the reaction is fully utilized and scientific means are adopted to prevent pollution from the beginning, so the process and terminal are zero emissions and zero pollution, which is a kind of chemistry to prevent pollution from the source. Green chemistry is different from environmental protection. Green chemistry does not passively control environmental pollution, but actively prevents chemical pollution, thus fundamentally cutting off pollution sources. Therefore, green chemistry is a higher level of environment-friendly chemistry. 2.2 the emergence and background of green chemistry today, the concept of sustainable development has been widely recognized by the world. It emphasizes the coordinated development of population, economy, society, environment and resources, which means not only developing economy, but also protecting natural resources and environment so that future generations can develop sustainably. Green chemistry is a sustainable development theory based on the harmonious development between man and nature. 1984 "waste minimization" is put forward by the us environmental protection agency, which is the original idea of green chemistry. 1989 The US Environmental Protection Agency put forward the concept of "pollution prevention". 1990, the federal government of the United States passed the Pollution Prevention Action Act, which established pollution prevention as a national policy, and the word "green chemistry" appeared for the first time in the provisions of this law. 1992, the us environmental protection agency issued the pollution prevention strategy. From 65438 to 0995, the US government established the "Presidential Green Chemistry Challenge Award". From 65438 to 0999, the Royal Society of Chemistry founded the first international journal of green chemistry, which marked the official appearance of green chemistry. China is also closely following the forefront of chemical development in the world. 1995, the Department of Chemistry, Chinese Academy of Sciences determined the green chemistry and technical consultation topic for academicians. 2.3 The core content of green chemistry Atomic economy is the core content of green chemistry. This concept was first put forward by Trost, a famous organic chemist at Stanford University in the United States, in 199 1 (for which he won the 1998 "Presidential Green Chemistry Challenge Award"), that is, what percentage of atoms in raw material molecules have been converted into products? The ideal atomic economic reaction is that 100% of atoms in raw material molecules are converted into products, and no by-products or wastes are produced, thus realizing "zero emission" of wastes. He used the atom utilization rate to measure the atom economy of the reaction, and thought that efficient organic synthesis should make maximum use of every atom of the raw material molecule and combine with the target molecule. The atomic economic reaction of green chemistry has two obvious advantages: one is to maximize the use of raw materials, and the other is to minimize the discharge of waste. The expression of atomic utilization ratio is: atomic utilization ratio = (sum of formula amount of expected products/formula amount of reaction substances) × 100%. For example, the preparation of pollution-free oxidant hydrogen peroxide can adopt ethyl anthraquinone method, that is, hydrogen and oxygen can be directly synthesized under the catalysis of 2-ethylanthraquinone and Pd, and 2-ethylanthraquinone can be recycled. The atomic utilization rate of this reaction is 100%, which reflects the atomic economy, reduces the generation and discharge of waste, and is a typical zero emission. 2.4 12 principle and 5R principle of green chemistry In order to briefly describe the main points of green chemistry, P.T.Anastas and J.C.Waner once put forward the 12 principle of green chemistry, which has certain guiding role for our future research on green chemistry. First, prevention-it is much better to prevent waste from being produced than to treat and purify it after it is produced. ⅱ. Talking about atomic economy-such a synthetic scheme should be designed so that the materials used in the reaction process can enter the final product to the maximum extent. Three. Harmless synthetic reaction occurs-in any case, feasible methods should be adopted, and only substances with little toxicity to human body or environment should be selected or produced. Ⅳ. Design to make the generated chemical products safe —— Design the products of chemical reaction not only have the required properties, but also have the minimum toxicity. ⅴ. Solvents and auxiliary materials are safer-try not to use harmless auxiliary materials (such as solvents or precipitants) as a last resort. ⅵ. In the design, the use of energy should pay attention to efficiency-reduce the energy required for chemical process as much as possible, and at the same time consider the environmental and economic benefits. The synthesis process is carried out at atmospheric temperature and pressure as much as possible. ⅶ. Use recyclable raw materials-as long as it is technically and economically feasible, raw materials should be recycled rather than deteriorated. ⅷ. Minimize derivative reactions-We should avoid or reduce redundant derivative reactions as much as possible (to temporarily change the physical and chemical processes in order to protect groups or remove protection), because these steps need to add some reactants and also produce waste. ⅸ. Catalysis-Catalysts (as selective as possible) are more important than stoichiometric reactants. ⅹ. Design degradation-The products produced according to the design can be decomposed into harmless degradation products after their effective functions are completed, and will not continue to exist in the environment. ⅶ. The pollution prevention process can be analyzed in real time-analytical methods must be continuously developed to monitor the analysis and process in real time, especially the control of harmful substances. Especially from the safety of chemical reactions to prevent accidents-in the chemical process, the selection of reactants (including their specific forms) should focus on minimizing the possibility of chemical accidents including release, explosion and fire. In order to express the requirements of green chemistry for resource utilization more clearly, people put forward 5R theory: Ⅰ. Reduction-reduction is put forward from the perspective of saving resources and reducing pollution. One of the effective ways to reduce the dosage and how to reduce the dosage while protecting the output is to improve the conversion rate and reduce the loss rate. ② Reduce the discharge of "three wastes". Mainly to reduce the emission of waste gas, waste water and waste (by-products), which must be lower than the emission standard. Two. Reuse-Reuse-Reuse is the need to reduce costs and waste. Such as catalysts and carriers in chemical industry, we should consider the design of reuse from the beginning. Three. Recovery-recycling recovery mainly includes: recovering unreacted raw materials, by-products, cosolvents, catalysts, stabilizers and other unreacted reagents. ⅵ. Regeneration-Regeneration is an effective way to turn waste into treasure, save resources and energy, and reduce pollution. It requires that the recycling of raw materials should be considered in the process design of chemical product production. ⅴ. Rejection-Rejection is the most fundamental way to eliminate pollution. Refers to the refusal to use some irreplaceable, non-recyclable, non-renewable and non-reusable raw materials with obvious toxic and side effects and pollution. 3. The development prospect of green chemistry 3. 1 The greening of reaction raw materials means that the reaction raw materials conform to the 5R principle. 3.2 Atomic Economic Reactions In the production of basic organic raw materials, there have been some examples of atomic economic reactions, such as hydroformylation of propylene to butyraldehyde, carbonylation of methanol to acetic acid, and synthesis of adiponitrile from butadiene and hydrocyanic acid. 3.3 Efficient synthesis method does not involve separation. Efficient multi-step synthesis is undoubtedly an important part of clean technology. 3.4. Improve the selectivity of reaction-oriented synthesis such as asymmetric synthesis. 3.5. Environmentally friendly catalyst For example, in the cracking reaction of n-hexane, solid acid SiO _ 2-AlCl _ 3 has better selectivity and less corrosiveness than ordinary AlCl _ 3. 3.6. Physical methods promote chemical reactions such as microwave initiation and promotion of Diels Alder reaction, Claisen rearrangement, condensation and many other important organic reactions. 3.7. Enzymatic organic chemical reaction Enzymatic organic chemical reaction has the characteristics of high efficiency, selectivity, mild reaction conditions and environmental friendliness. 3.8 The chemical pollution of solvents not only comes from raw materials and products, but also relates to the solvents used in reaction medium, separation and formula. The research on substitutes for toxic volatile solvents is an important research direction of green chemistry. Such as supercritical fluid, organic synthesis in aqueous phase and room temperature molten salt solvent. 3.9. Computer-aided green chemistry design and simulation In the field of chemistry and chemical engineering, computers have been widely used in structural activity analysis, structural analysis, reactivity prediction, fault diagnosis and control and many other aspects. There is no doubt that computers have promoted the faster development of green chemistry in finding the best reaction route, optimizing chemical processes and designing products. 3. 10 environmental protection products such as degradable plastics, environmental protection pesticides, green fuels, green coatings and chlorofluorocarbon substitutes. Green chemistry has injected new vitality into the development of chemistry, and chemistry will be promising in 2 1 century.