Green Chemistry: Theory and Practice

P. T. Anastas J. C. Warner Oxford University Press: 1998. 134pp £45, $85

P. T. AnastasT. C. Williamson

Green Chemistry: Frontiers in Benign Chemical Synthesis and Processes

Oxford University Press: 1998. 364 pp.£65, $115

In 1856, W. H. Perkin, who was 18 years old at the time, attempted to synthesize quinine by dichromate oxidation of a raw material obtained from distilled coal tar. This resulted in the serendipitous discovery of the first synthetic dye, aniline purple. Within a few years a commercial plant was in operation, and this is generally recognized as the first industrial organic synthesis. The organic chemical industry was born, and the next 100 years witnessed the remarkable contributions of synthetic organic chemistry in increasing life expectancy, providing food, clothing and shelter and improving the quality of life in general.

The turning point in this remarkable success story came in the early 1960s, with the realization that a price was being paid for these achievements. The publication of Rachel Carson's Silent Spring in 1962 alerted the public to the negative effects of the accumulation of synthetic chemicals, such as DDT, in the environment. The environmental movement was born, and for the next three decades much effort was devoted to studying the effects of various synthetic chemicals on the environment, a recent example being the role of chlorofluorocarbons in the depletion of atmospheric ozone. The emphasis was clearly on the products rather than on the processes by which they were being produced.

In the 1990s, we are now focusing on the processes used in synthesizing organic chemicals. And the conclusion is clear: many of these processes generate enormous waste, for example as inorganic salts in aqueous effluents and volatile organic molecules in air emissions. The cause is also clear: many industrial organic syntheses use antiquated technologies involving stoichiometric inorganic reagents such as the dichromate oxidation used by Perkin almost a century and a half ago. Historically, as Paul Anastas and John Warner point out in Green Chemistry: Theory and Practice , synthetic chemists have not been particularly environmentally conscious, since their involvement was at the beginning of the chemical synthetic chain whereas problems were mostly encountered at its end.

The solution is the replacement of these technologies with cleaner catalytic alternatives. The emphasis is on eliminating waste at source — primary pollution prevention — rather than finding incremental end-of-pipe solutions. This has now become known as green chemistry, and is defined by Anastas and Warner as: “The utilization of a set of principles that reduces or eliminates the use or generation of hazardous substances in the design, manufacture and application of chemical products”. The tools of green chemistry are alternative feedstocks, solvents and reagents, and catalytic versus stoichiometric processes. And the book introduces and explains the concept of atom efficiency in organic synthesis — fundamental to pollution prevention. (However, I found the treatment rather superficial, and was surprised to read that light is considered a feedstock.)

Hence, the concept of green chemistry encompasses both alternative products and alternative processes. It is a useful working definition, but concentrates too much, for my taste, on hazardous substances rather than the goal of reducing all waste (zero-emission plants).

The book defines the 12 principles of green chemistry — described as the Hippocratic oath for chemists. The first principle is that it is better to prevent waste than to treat or clean up waste after it is formed; the other 11 can be roughly paraphrased as: processes should be atom- and energy-efficient, use renewable rather than depleting raw materials and avoid using toxic and/or hazardous reagents and solvents, and products should be designed for non-persistence in the environment. The concept of green chemistry is closely related to, or perhaps even synonymous with, that of sustainability (defined as the ability to maintain the development of the quality of life while not compromising the ability of our progeny to do the same).

The examples of green chemistry used are predominantly taken from the Green Chemistry Challenge Awards, which are sponsored by the US Environmental Protection Agency and, consequently, are heavily biased towards the United States. And some are rather contrived — a broad scope is implied for a photochemical alternative to Friedel Crafts acylation, but it is actually very limited.

Anastas and Warner's prediction of future trends is a mixed bag of well-defined goals, for example new catalytic oxidation technologies with O2or H2O2, and rather nebulous and/or contrived concepts such as “biomimetic multifunctional reagents” and “combinatorial green chemistry” (whatever that may be).

Green Chemistry: Frontiers in Benign Synthesis and Processes , edited by Anastas and Tracey Williamson, his colleague at the Environmental Protection Agency, contains more chemistry for chemists to get their teeth into. It is a useful collection of articles devoted to different aspects of green chemistry and is complementary to the Anastas/ Warner book. One chapter (and the foreword) is written by Barry Trost, the champion of atom efficiency in organic synthesis.

Again, however, the contributions are overwhelmingly biased towards US academia and, as a result, the examples tend to be rather dry and concentrate on the authors’ own work, thereby failing to provide either an overview or industrial relevance for the topics. It is also a pity that there are not more contributions from industrial groups — Monsanto, Mitsubishi, Rhône-Poulenc and Lonza come readily to mind.