Martyn Poliakoff

The Structure of [Fe(CO)4]—An Important New Chapter in a Long‐Running Story

The structure of the singlet state (1 A1 ) of [Fe(CO)4 ] in the gas phase has been determined by a combination of laser photochemistry of [Fe(CO)5 ] and electron diffraction imaging. The ground state of [Fe(CO)4 ] is known to be a triplet species (3 B2 ), and this is the species detected in picosecond time-resolved IR experiments with [Fe(CO)5 ] in solution. This is an appropriate moment to survey the state of knowledge on [Fe(CO)4 ], beginning from the first low-temperature matrix experiments.

Valorization of Biomass: Deriving More Value from Waste

Most of the carbon-based compounds currently manufactured by the chemical industry are derived from petroleum. The rising cost and dwindling supply of oil have been focusing attention on possible routes to making chemicals, fuels, and solvents from biomass instead. In this context, many recent studies have assessed the relative merits of applying different dedicated crops to chemical production. Here, we highlight the opportunities for diverting existing residual biomass—the by-products of present agricultural and food-processing streams—to this end.

Sustainable technology: Green chemistry

Modern life depends on the petrochemical industry — most drugs, paints and plastics derive from oil. But current processes for making chemical products are not sustainable in terms of resources and environmental impact. Green chemistry aims to tackle this problem, and real progress is being made.

Chemical reactions in supercritical carbon dioxide: from laboratory to commercial plantThis work was presented at the Green Solvents for Catalysis Meeting held in Bruchsal, Germany, 13–16th October 2002.

The application of supercritical carbon dioxide in continuous, fixed bed reactors has allowed the successful development of a variety of industrially viable synthetic transformations. The world’s first, multi-reaction, supercritical flow reactor was commissioned in 2002 as a direct result of the successful collaboration between the Clean Technology Group at the University of Nottingham and the fine chemicals manufacturer, Thomas Swan & Co. Ltd. We highlight the development of this project from laboratory to plant scale, particularly in the context of the hydrogenation of isophorone. Phase data for the system; isophorone + H2 + CO2, are presented for the first time. Overall, we present a progress report about an on-going Green Chemistry initiative that has successfully forged strong links between Industry and Academia.

Continuous reactions in supercritical carbon dioxide: problems, solutions and possible ways forward

This Tutorial Review focuses on supercritical carbon dioxide (scCO(2)), and discusses some of the problems that have frustrated its wide use on an industrial scale. It gives some recent examples where strategies have been developed to reduce the energy requirements, including sequential reactions and gas-expanded liquids. It then describes a number of cases where scCO(2) offers real chemical advantages over more conventional solvents, for example by controlled phase separation, tunable selectivity, oxidation and on-line analysis and self-optimisation. Overall, this review indicates where scCO(2) could deliver value in the future.

Synthesis of benzimidazoles in high-temperature water

The objective of this research was to conduct constructive organic chemistry in water and to achieve yields that were comparable to, or better than, those in conventional media. The synthesis of 2-phenylbenzimidazole from 1,2-phenylenediamine and benzoic acid was chosen as a benchmark reaction. The reaction parameters, such as temperature, density and reaction time, have been systematically studied to understand whether the solvent properties of high-temperature water can have a positive effect on the chemistry. The reaction was performed in a new design of batch-type autoclave and was also monitored in situ by UV-vis spectroscopy. By tuning the parameters, the yield has been optimised to around 90%. The optimised conditions were then applied to related benzimidazoles, some of which crystallised from solution in situ to yield single crystals that were sufficiently pure to be analysed directly by X-ray diffraction, without any further purification.

A principled stance

In Chinese, chemistry is the ‘mixing science’, whereas in Dutch, it’s the ‘separation art’. But whatever their nationality, academic chemists often do not know in detail how the chemicals they use are made, or how their chemistry affects the biosphere. They view industrial chemistry as meat-eaters view the slaughterhouse — the gory details are glossed over and the fate of the waste is ignored. On the other hand, much of the general public recoils at the mere mention of ‘chemicals’, yet we are all clothed, fed, washed and transported by the products of the chemical and pharmaceutical industries. While we benefit from increased quality and length of life thanks to chemicals, the industry that makes them is frequently accused of degrading the Earth. Society relies on chemicals. Like a good cook, the industrial chemist recycles waste. Yet many types of waste are dangerous, leaving no option but costly disposal. With the global population rising and standards of living increasing, current methods of chemical production are unsustainable. As production rises to meet demand, waste levels will soar and landfill sites will be exhausted. Manufacturers will be increasingly restricted by environmental legislation; enforcement agencies will become increasingly overloaded; and costs of waste treatment will stifle innovation. A new approach is needed to remould attitudes constructively, and to attract young people to the field of chemistry. Step forward ‘green chemistry’, which aims to create products that are as harmless as possible and therefore require less regulation. The concept is enshrined in a set of 12 principles, ranging from minimizing waste to avoiding accidents. Individually, these principles are not new; what is potentially revolutionary is grouping them together so that chemists can focus on using classical chemistry to design products with less environmental impact. For example, non-toxic carbon dioxide is now used to make lighter, stronger building materials and to replace chlorinated organic solvents in chemical reactions and dry-cleaning. Integrating energy, waste and toxicity issues when thinking about new processes and reactions has proved to be very effective. Although some industrial processes are efficient, others are extremely wasteful, requiring costly handling and disposal of chemicals. The more stages a chemical process involves, the more potential it has for creating waste. So green chemistry inspires a kind of chemical ‘golf match’, in which fewer steps represent a better environmental ‘score’ — and the best result is, of course, a hole in one. For example, a new process for producing the anti-inflammatory drug ibuprofen halves the number of steps, makes them all catalytic and more than doubles the atom efficiency of the process. Green chemistry not only leads to cleaner and more efficient processes, but can increase profitability by eliminating many of the traditional costs of treatment, disposal, liability and regulatory compliance. Green chemistry involves more than just tidying up existing processes — if it were that simple, process economics would already be driving manufacturers in that direction. Rather, it identifies a need to design new, safer molecules. Often, the toxicity and the usefulness of a compound arise from different parts of the molecule; for example, a couple of strategically placed methyl groups added to a dye molecule makes it much less toxic but leaves its dyeing properties intact. Similar minor structural modifications can increase the biodegradability of molecules and reduce their environmental impact. Linking structure and toxicity gives synthetic chemists a new perspective, allowing them to design new pesticides that are toxic only to target organisms, with a fraction of the usual dose, and which do not persist in the environment. Green chemistry has captured the imagination of many chemists. But some industrial chemists believe that their very successful efforts at cleaning up have been overlooked, and some academics fear that green chemistry is ‘soft’ science. Although understandable in historical contexts, neither view is correct. Green chemistry is a new partnership, bringing together the efforts of industrial and academic research and building rapidly on the past successes of both. New solvents, feedstocks, catalysts and processes, producing everything from new, biologically derived, renewable plastics to lead-free automotive paint, are being developed throughout the world. Many challenges remain. How can chemical production shift from unsustainable petroleum feedstocks to renewable biomass? Can some of the vast quantities of carbon dioxide vented into the atmosphere be converted into useful chemicals? Can the environmental impact of agrochemicals be reduced while increasing food production? Green chemistry will attract the new generation of chemists needed to solve these problems. Already, young people are beginning to see chemistry as a key to saving our environment rather than a tool for its destruction. Will green chemistry take over all of chemistry? Far from it — the revolution of one generation becomes the orthodoxy of the next. The 12 principles are so obvious that chemists of the future will wonder why it took so long to integrate them into the mainstream. After all, why make chemicals wastefully and expensively, when they can be produced cheaply and cleanly? ■ Martyn Poliakoff is a research professor and Paul Anastas is a special professor at the School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, UK.

Continuous catalytic reactions in supercritical fluids

Abstract Recent heightened awareness of the environmental impacts associated with a large proportion of established chemical processes has led to the application of considerable pressures on the chemical industry, both regulatory and consumer driven, to adopt a cleaner and greener approach to manufacture. The economies of scale and associated efficiencies of continuous processes have long been a contributing factor in the design and efficient running of many large-scale industrial plants. When successfully combined with a versatile and environmentally benign solvent system such as supercritical fluids (SCFs), continuous processing can be seen to be suitable for a wide variety of reactions (hydrogenation, hydroformylation, alkylation, etc.). which can be conducted efficiently in an environmentally sensitive way. This review article aims to show the reader how the marriage of these two technologies is helping chemistry to achieve this goal.

The 24 Principles of Green Engineering and Green Chemistry: “IMPROVEMENTS PRODUCTIVELY”

Samantha Tang, Richard Bourne, Richard Smith and Martyn Poliakoff suggest a condensed 24 Principles of Green Chemistry and Green Engineering, with the mnemonic “IMPROVEMENTS PRODUCTIVELY”

A critical look at reactions in class I and II gas-expanded liquids using CO2 and other gases

This short review aims to give a summary of the publications on reactions in class I and II gas-expanded liquids (GXLs) (those with organic or aqueous liquid components), and to draw conclusions from the trends in the current literature.