Industrial fine chemicals catalysis

Heterogeneous Catalysis in the Fine Chemical and Pharmaceutical Industries... 

Catalysts are extensively used and have played a huge role in making bulk chemical manufacturing technology more competitive and environmentally fnendly. Undoubtedly catalysis will continue to provide the answer to many economic and environmental challenges currently faced by industry. As indicated above catalysts are now needed by the fine chemical and pharmaceutical industries, and they need to be robust, selective, recoverable and reusable. 

With reference to two products of your choice discuss the role catalysts have played in the development of a more economic and environmentally friendly bulk chemical industry. Why has catalysis had less impact on the development of fine and pharmaceutical products ... 

For example, living matter relies on enzymes, which are the most specific catalysts one can think of. Also, the chemical industry cannot exist without catalysis, which is an indispensable tool in the production of bulk chemicals, fine chemicals and fuels. 

Industrial applications inclnde the production of petrochemicals, fine chemicals and pharmacenticals (particnlarly throngh asymmetric catalysis), hydrometallurgy, and waste-treatment processes. Many life processes are based on metallo-enzyme systems that catalyse redox and acid-base reactions. 

Catalysis opens reaction pathways that are not accessible to uncatalysed reactions. It should be self-evident that thermodynamics predict whether a reaction can occur. So, catalysis influences reaction rates (and as a consequence selectivities), but the thermodynamic equilibrium still is the boundary. Catalysis plays a key role in chemical conversions, although it is fair to state that it is not applied to the same degree in all sectors of the chemical industry. While in bulk chemicals production catalytic processes constitute over 80 % of the industrially applied processes, in fine chemicals and specialty chemicals production catalysis plays a relatively modest role. In the pharmaceutical industry its role is even smaller. It is the opinion of the authors that catalysis has a large potential in these areas and that its role will increase drastically in the coming years. However, catalysis is a multidisciplinary subject that has a lot of aspects unfamiliar to synthetic chemists. Therefore, it was decided to treat catalysis in a separate chapter. 

Homogeneous catalysis has an important role to play in enantioselective reactions. To improve product safety, the pharmaceutical industry is producing an increasing number of products in enantiomerically pure form. Other important (future) markets include agrochemicals, polymers and fine chemicals. Although the number of practised processes is quite small the potential is high. 

Table 3.12 surveys current industrial applications of enantioselective homogeneous catalysis in fine chemicals production. Most chiral catalyst in Table 3.12 have chiral phosphine ligands (see Fig. 3.54). The DIP AMP ligand, which is used in the production of L-Dopa, one of the first chiral syntheses, possesses phosphorus chirality, (see also Section 4.5.8.1) A number of commercial processes use the BINAP ligand, which has axial chirality. The PNNP ligand, on the other hand, has its chirality centred on the a-phenethyl groups two atoms removed from the phosphorus atoms, which bind to the rhodium ion. Nevertheless, good enantio.selectivity is obtained with this catalyst in the synthesis of L-phenylalanine. 

Examples of industrially applied enantioselective homogeneous catalysis in fine chemicals (Parshall and Ittel, 1992 Cornils and Herrmann, 1996)... 

Figure 3.56 in Section 3.8 illustrates the mechanism of phase-transfer catalysis. Tables 4.4 and 4.5 give examples of industrial importance in agrochemicals, pharmaceuticals, fine chemicals, oleochemicals, etc. 

High throughput screening is one of the hot topics in heterogeneous catalysis. Advanced experimental techniques have been developed to screen and develop solid catalysts for gas-phase systems. However, for catalytic three-phase systems, rapid screening has got much less attention [1-6]. Three-phase catalysis is applied in numerous industrial processes, from synthesis of fine chemicals to refining of crade oil. 

Conjugated dienes are among the most significant building blocks both in laboratories and in the chemical industry [1], Especially, 1,3-butadiene and isoprene are key feedstocks for the manufacture of polymers and fine chemicals. Since the discovery of the Ziegler-Natta catalyst for the polymerizations of ethylene and propylene, the powerful features of transition metal catalysis has been widely recognized, and studies in this field have been pursued very actively [2-7]. 

The cost of the catalysts represents a major hurdle on the road to the industrial application of homogeneous catalysis, and in particular for the production of fine chemicals [1, 2], This is particularly true for chiral catalysts that are based on expensive metals, such as rhodium, iridium, ruthenium and palladium, and on chiral ligands that are prepared by lengthy total syntheses, which often makes them more expensive than the metals. In spite of this, the number of large-scale applications for these catalysts is growing. Clearly, these can only be economic if the substrate catalyst ratio (SCR) can be very high, often between 103 and 105. 

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