Greener Processes

However, these statements are generalizations, and it is not necessarily true to say that all biotransformations will be greener than the chemical alternative. Therefore, it is important to analyse each comparison objectively on a case-by-case basis using a multivariate process to take into account the complexity of the analysis. Designing greener processes involves, for example ... 

In order to recover both amines in ophcaUy achve form the amide is hydrolyzed chemically by reachon with NaOH in aqueous ethylene glycol at 150 °C. This brute force method would certainly lead to problems with amines containing other functional groups and is in stark contrast to the elegant enzymatic procedure used for the first step. Hence, an overall greener process can be obtained by employing an enzymatic deacylation step in what we have called an easy-on/easy-off process... 

To measure the scalability of a process it is necessary to understand the chemistry and reaction kinetics involved and then to determine their impact on well-defined critical quality attributes desired of the product in order to find the optimum processing window within which there is certainty that the product will be of acceptable quality. However, these data are not readily available for many pharmaceutical chemistry reactions, so a subjective measure of a the scalability, robustness, and greenness of many processes has been developed by Pfizer based on operator knowledge and experience to assist development teams both in the laboratory and in pilot plants to develop greener processes [28]. 

F. van Rantwijk, and R. A. Sheldon, Enzymatic coupling using a mixture of side chain donors affords a greener process for ampicillin, Green Chem. 2001, 3, 316-319. 

The future of C02 technology appears to be bright. We have seen a number of new developments for chemical and materials processing to the point of emerging industrial and commercial applications. As the number of laboratories in academia, government, and industry that are investigating the utilization of C02 continues to increase, we expect more applications that lead to greener processes. 

The contribution of fluorine chemistry to the field of clean chemical technology is reviewed. The roles of fluorochemicals in the environment and the ways in which they may be involved in inherently greener processes are discussed. 

An environmentally greener process for the synthesis of HFCs can be envisioned through an intermediate inorganic metal fluoride that is capable of fluor-inating a C-H bond of a desirable hydrocarbon and could be regenerated to the appropriate oxidized metal fluoride with oxygen and HF. The general synthetic approach is shown in equations (6a) and (6b) and the net reaction is shown in equation (6c). 

Solvents are, perhaps, the greatest concern when developing greener processes. Solvents are necessary since they provide a medium for... 

Fig. 6.3. Green engineering example conventional versus greener process using reactive Distillation technologies for the production of high-purity metal acetate (Adapted from Malone and Russ4 and modified.)...

Renewable raw materials can contribute to the sustainability of chemical products in two ways (i) by developing greener, biomass-derived products which replace existing oil-based products, e.g. a biodegradable plastic, and (ii) greener processes for the manufacture of existing chemicals from biomass instead of from fossil feedstocks. These conversion processes should, of course, be catalytic in order to maximize atom efficiencies and minimize waste (E factors) but they could be chemo- or biocatalytic, e.g. fermentation [3-5]. Even the chemocatalysts themselves can be derived from biomass, e.g. expanded com starches modified with surface S03H or amine moieties can be used as recyclable solid acid or base catalysts, respectively [6]. 

In the USA the Presidential Green Chemistry Challenge Awards [7] were introduced to stimulate the application of the principles of green chemistry and many chemical and pharmaceutical companies have received awards for the development of greener processes and products, e.g. Pfizer for developing a greener process for sildenafil manufacture (see Chapter 7). 

---