The 12 principles of green chemistry were originally reported by Anastas1 in the form shown in Box 1 and later as the mnemonic shown in Box 2 by Poliakoff.2 A feature of these principles is the use of catalytic reagents to accomplish chemical transformations. The development of catalysts for important chemical transformations certainly predates any notion of green chemistry and has been a major feature of research in all areas of chemistry for almost 150 years. Thus, physical chemists and material scientists have dominated the development of heterogeneous catalysis; physical and physical organic chemists have developed tools to allow catalytic cycles to be determined. Inorganic and organic chemists have developed new ligands and catalysts for homogeneous metal-based catalysts and organic chemists have shown that metal-free asymmetric catalysis can be achieved. Finally, biological chemists have studied the mechanisms of enzyme-catalysed reactions and developed new biochemical tools that allow the structure of enzymes to be modified to enhance their catalytic activity for a particular substrate, or even allow them to catalyse a different reaction.
It is better to prevent waste than to treat or clean up waste after it is formed.
Synthetic methods should be designed to maximise the incorporation of all materials used in the process into the final product.
Wherever practicable, synthetic methodologies should be designed to use and generate substances that possess little or no toxicity to human health and the environment.
Chemical products should be designed to preserve efficacy of function while reducing toxicity.
The use of auxiliary substances (e.g. solvents, separation agents etc.) should be made unnecessary wherever possible and innocuous when used.
Energy requirements should be recognized for their environmental and economic impact and should be minimized. Synthetic methods should be conducted at ambient temperature and pressure.
A raw material or feedstock should be renewable rather than depleting wherever technically and economically practicable.
Unnecessary derivatization (blocking group, protection/deprotection, temporary modification of physical/chemical processes) should be avoided whenever possible.
Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.
Chemical products should be designed so that at the end of their function they do not persist in the environment and break down into innocuous degradation products.
Analytical methodologies need to be further developed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances.
Substances and the form of a substance used in a chemical process should be chosen so as to minimise the potential for chemical accidents, including releases, explosions and fires.
P – Prevent wastes
R – Renewable materials
O – Omit derivatization steps
D – Degradable chemical products
U – Use safe synthetic methods
C – Catalytic reagents
T – Temperature, pressure ambient
I – In process monitoring
V – Very few auxiliary substances
E – E-factor, maximise feed in product
L – Low toxicity of chemical products
Y – Yes, it is safe
There have been some remarkable achievements in catalyst development recognised by numerous Nobel prizes for work done in this area (Box 3) and catalysis has progressed to the stage where it is now difficult to imagine a reaction that cannot be achieved catalytically. However, examination of the catalytic literature shows that the majority of catalysts developed, and many that are in commercial use rely upon the use of metals or other elements whose abundance in the Earth's crust is very limited and that are being rapidly consumed. This is illustrated in Figure 1 for papers on asymmetric catalysis published between 1999 and 2005.3
2010: Richard F. Heck, Ei-ichi Negishi and Akira Suzuki for palladium-catalysed cross couplings in organic synthesis.
2007: Gerhard Ertl for studies of chemical processes on solid surfaces
2005: Yves Chauvin, Robert H. Grubbs and Richard R. Schrock for the development of the metathesis method in organic synthesis.
2001: William S. Knowles, Ryoji Noyori and K. Barry Sharpless for work on chirally catalysed hydrogenation and oxidation reactions.
1997: Paul D. Boyer, John E. Walker and Jens C. Skou for the elucidation of the enzymatic mechanism underlying the synthesis of adenosine triphosphate (ATP) and the first discovery of an ion-transporting enzyme, Na+, K+ -ATPase.
1989: Sidney Altman and Thomas R. Cech for the discovery of the catalytic properties of RNA.
1975: John Warcup Cornforth and Vladimir Prelog for work on the stereochemistry of enzyme-catalyzed reactions and research into the stereochemistry of organic molecules and reactions.
1972: Christian B. Anfinsen, Stanford Moore and William H. Stein for work on ribonuclease, especially concerning the connection between the amino acid sequence and the biologically active conformation and for contribution to the understanding of the connection between chemical structure and catalytic activity of the active centre of the ribonuclease molecule.
1963: Karl Ziegler and Giulio Natta for their discoveries in the field of the chemistry and technology of high polymers.
1929: Arthur Harden and Hans Karl August Simon von Euler-Chelpin for their investigations on the fermentation of sugar and fermentative enzymes.
1918: Fritz Haber for the synthesis of ammonia from its elements.
1912: Victor Grignard and Paul Sabatier for the discovery of the so-called Grignard reagent, which in recent years has greatly advanced the progress of organic chemistry and for the method of hydrogenating organic compounds in the presence of finely disintegrated metals whereby the progress of organic chemistry has been greatly advanced in recent years.
1909: Wilhelm Ostwald in recognition of his work on catalysis and for his investigations into the fundamental principles governing chemical equilibria and rates of reaction.
Importance of various metals in asymmetric catalysis. (Reprinted with permission from (D. J. Ramón and M. Yus, Chem. Rev. 2006, 106, 2126). (Copyright (2006) American Chemical Society).
Importance of various metals in asymmetric catalysis. (Reprinted with permission from (D. J. Ramón and M. Yus, Chem. Rev. 2006, 106, 2126). (Copyright (2006) American Chemical Society).
The availability of chemical elements depends on many factors as discussed in Chapter 1 of Sustainable Catalysis: With Non-endangered Metals, Part 1. With the exception of helium, which is too light to be held by the Earth's gravity and so is lost to space, chemical elements are not actually being lost to planet Earth, rather they are being transferred from relatively rich ores to much more diluted waste sites from where, in most cases, it is not currently economically viable to recover them. This, combined with growing demand for many elements, often low recycling rates and geographical and political restrictions on ore availability leads to the concept of elemental sustainability. One pictorial representation of elemental sustainability is shown in Figure 2,4 and this, along the British Geological Survey 2012 Risk list (BGS2012)5 which ranked the supply risk of elements from 10 (high) to 1 (low) forms the basis of the rest of this book. Thus, catalysts that contain only elements coloured green or orange in Figure 2 and that have a relative supply risk index of 7.6 or lower in the BGS2012 are included in this book with three exceptions. Palladium would have been borderline to include (orange in Figure 2 and supply risk index of 7.6 in BGS2012), but has been excluded as it is so widely used in catalysis that it would have required a separate volume to cover its use in catalysis. A chapter on scandium and yttrium based catalysts was planned but could not be delivered due to the author's ill health.
A periodic table illustrating the endangered nature of chemical elements.
After an introductory chapter on elemental sustainability, the first two volumes of this work, Sustainable Catalysis: With Non-endangered Metals, Parts 1 and 2, deal with sustainable metal based catalysts. Within each subsequent chapter, the authors have been asked to exclude any catalyst that contains ligands containing endangered elements (e.g. phosphorus) and to highlight any examples that have other sustainable features (use of green solvent, high atom economy, etc.). Where appropriate, elements have been grouped together (e.g. the alkali metals in Chapter 2) and those metals that are most commonly used in catalysis have been given multiple chapters: Chapters 4–7 for titanium, 12–13 for iron and 18–19 for aluminium. The final three chapters of Part 2 deal with thallium, tin and lead based catalysts. These are included for completeness as they meet the requirements outlined above, though the toxicity of many species containing these metals limits their green credentials.
Sustainable Catalysis: Without Metals or Other Endangered Elements, Parts 1 and 2 deal with catalysts that do not possess a metal centre as part of their structure. After an introductory chapter, Chapters 2–4 cover non-asymmetric acid and base catalysis. The subsequent chapters (5–24) deal with asymmetric organocatalysis as this area has exploded in importance over the last 20 years. Again, catalysts that contain endangered elements (e.g. phosphorus) have been excluded and authors were asked to highlight any examples that have other sustainable features (use of green solvent, high atom economy, etc.).
It is hoped that this four-volume work will be of use to anyone working in catalysis with an interest in green and sustainable chemistry, whether they be PhD students just starting in research, more established researchers in academia or industry, or educators looking for a source of material for a course to educate the next generation of chemists.
