Green Synthetic Processes and Procedures

Roberto Ballini, Roberto Ballini

• Publisher: Royal Society of Chemistry
• Year: 2019
• ISBN:
  9781788018395
• Edition: 1
• Topic: Scienze fisiche
• Subtopic: Chimica organica

The principles of Green Chemistry aim to improve the sustainability of chemical processes and reduce the generation of hazardous substances. There has been great growth in the field over the past few years and the number of research groups working in this area is still increasing. Now one of the biggest challenges is to embed the Green Chemistry ideals of safety and sustainability as standard, both in industry and academia. In order to do this, it is important to create resources that detail different applications and approaches.

Green Synthetic Processes and Procedures brings together expert contributors from across a number of areas of green synthesis to cover a diverse array of subjects. Providing a thorough overview of the current green synthetic toolbox, from biocatalysis to sonochemistry, this book is a useful resource for any chemist wishing to design cleaner and safer processes.

CHAPTER 1

Sustainability of Green Synthetic Processes and Procedures^†

István T. Horváth^*a and Edit Cséfalvay ^b

^a City University of Hong Kong, Department of Chemistry, Tat Chee Avenue, Kowloon, Hong Kong;

^b Department of Energy Engineering, Faculty of Mechanical Engineering, Budapest University of Technology and Economics, Budapest, Hungary
^*E-mail: [email protected]

Although the ecological footprint was perhaps the first green metric, the atom economy and E-factor have become the key metrics of green chemistry by providing the mass balance of chemical reactions and processes at the molecular level. Sustainability was poorly defined originally, since the key requisite to accurately forecast the needs of future generations remains difficult to pinpoint. Consequently, sustainability was replaced with suitability by many stake holders, as they had vested and/or conflicts of interests to label suitable developments sustainable. The sustainable development goals recently introduced by the United Nations seem to serve as a ‘roadmap to happiness’ instead of metrics. A simple and independent definition of sustainability was recently provided: Nature's resources, including energy, should be used at a rate at which they can be replaced naturally, and the generation of wastes cannot be faster than the rate of their remediation by Nature. The ethanol equivalent, the sustainability values of resource replacement and fate of waste, and the sustainability indicator have been recently defined to measure the sustainability of biomass-based carbon-chemicals and renewable energy. The production of ethylene, propylene, toluene, xylenes, styrene, and ethylene oxides cannot be sustainable due to the limited amount of bioethanol. The required volume of corn and the corresponding size of land are only enough to replace one sixth of fossil resources in the USA, EU, and China, and practically insufficient in Canada and the Russian Federation. Until the utilization of electricity becomes practical and economical in aviation, biomass-based liquid fuels are the sustainable alternative.

1.1 Development and Definition of Green Chemistry

Green chemistry emerged in the 1990s to address the increasing number of health and environmental issues caused by hazardous chemicals and materials. ¹ Their toxicity was either not considered or underestimated and sometimes even just simply ignored by some of the stake holders. The ecotoxicology of chemicals had received even less attention until the negative environmental and health effects of dichlorodiphenyl-trichloroethane, DDT, were reported by Raphael Carson in 1962. ² The number of serious environmental and health problems has rapidly increased in the second half of the last century, mostly due to the frantic expansion of the chemical, petrochemical, and pharmaceutical industry to supply all the goods and services for better quality of life of the growing population, as well as to generate more and more profits at the expense of the environment and population. ³ Some of the worst examples include the addition of tetraethyl lead to gasoline, ⁴ use of thalidomide by pregnant women, ^3b utilization of chlorofluorocarbons (CFCs) in refrigerators, ⁵ deadly accidents involving dioxins ^3b and methyl isocyanate, ^3b and contamination by crude oil, ⁶ dioxins, ^3b melamine, ⁷ and ammonia, ⁸ just to name a few. The emission of nitrogen oxides above the regulation level by hundred thousands of cheating cars for almost a decade ⁹ shows that profit making has remained more important than sustainability. While some of these health and/or environmental problems were the result of limited or lack of knowledge on toxicity, bioaccumulation, and ecotoxicity, others were simply due to fraudulent practices, individual or corporate greed, or both.

Environmental and health problems became so visible by the middle of the 1980s that the US Environmental Protection Agency switched the focus from ‘end-of-the-pipe clean-up’ approach to ‘pollution prevention’, which led to the enactment of the 1990 Pollution Prevention Act by the United States Congress. ¹⁰ In 1995, the traditional blue colour of the cover of Chemical Reviews, one of the flagship journals of the American Chemical Society, was changed to green for the one issue dedicated to environmental chemistry. ¹¹ The editorial included one of the earliest published definitions of green chemistry: “It is no longer sufficient to make marvellous new molecules solely on the basis of their marketable properties. Although marketability is an appropriate goal, we, as scientists, must also be concerned with our creations' potential for environmental impact”. The publication of the book entitled ‘Green Chemistry: Theory and Practice’ by Anastas and Warner in 1998 provided a carefully drafted definition: “Green chemistry is the utilization of a set of principles that reduces or eliminates the use or generation of hazardous substances in the design, manufacture, and applications of chemical products”. ¹² The prevention of the environmental and health impacts of hazardous chemicals, materials, and practices is addressed by the 12 principles of green chemistry (Box 1.1).

Box 1.1 The twelve principles of green chemistry ¹²

1. It is better to prevent waste than to treat or clean up waste after it is formed.
2. Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.
3. Wherever practicable, synthetic methodologies should be designed to use and generate substances that process little or no toxicity to human health and the environment.
4. Chemical products should be designed to preserve efficacy of function while reducing toxicity.
5. The use of auxiliary substances (e.g., solvents, separation agents, etc.) should be made unnecessary wherever possible and, innocuous when used.
6. Energy requirements should be recognized for their environmental and economic impacts and should be minimized. Synthetic methods should be conducted at ambient temperature and pressure.
7. A raw material of feedstock should be renewable rather than depleting wherever technically and economically practicable.
8. Unnecessary derivatization (blocking group, protection and deprotection, temporary modification of physical/chemical processes) should be avoided whenever possible.
9. Catalysts (as selective as possible) are superior to reagents.
10. Chemical products should be designed so that, at the end of their function, they d...