Route Selection

Even though many possibilities exist for the enantioselective preparation of enriched (S)-metolachlor, it was dear from the beginning that because of the relatively low price and the large volume ( 10000t/y) of the racemic product, only a catalytic route would be feasible. The following four synthetic routes were studied in some detail. 

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As the program moved forward to Phase III clinical studies an evaluation of the pros and cons of each approach was carried out to assist with route selection for long-term implementation (Table 9.10). 

Edwards and Lawrence (1993) have presented a list of sixteen chemical and physical properties and process parameters which are available at the process route selection stage (Table 5). Seven of these sixteen parameters were included to their index method (PUS). The selected parameters concentrate very much on the chemical process route and chemistry. They have also tested their selection by an expert judgement, which gave support to their work (Edwards et al., 1996). 

Figure 5. Geometries and energies relative to reactants of all the stationary points related to the associative route. Selected bond distances are given in A and energies in kJ mol 1.

This chapter surveys different process options to convert terpenes, plant oils, carbohydrates and lignocellulosic materials into valuable chemicals and polymers. Three different strategies of conversion processes integrated in a biorefinery scheme are proposed from biomass to bioproducts via degraded molecules , from platform molecules to bioproducts , and from biomass to bioproducts via new synthesis routes . Selected examples representative of the three options are given. Attention is focused on conversions based on one-pot reactions involving one or several catalytic steps that could be used to replace conventional synthetic routes developed for hydrocarbons. 

In addition to the presence of these elements in ores, they are also available from recycled feeds, such as catalyst wastes, and as an intermediate bulk palladium platinum product from some refineries. The processes that have been devised to separate these elements rely on two general routes selective extraction with different reagents or coextraction of the elements followed by selective stripping. To understand these alternatives, it is necessary to consider the basic solution chemistry of these elements. The two common oxidation states and stereochemistries are square planar palladium(II) and octahedral platinum(IV). Of these, palladium(II) has the faster substitution kinetics, with platinum(IV) virtually inert. However even for palladium, substitution is much slower than for the base metals so long as contact times are required to achieve extraction equilibrium. 

TKe % value shown ts ttie improve/nemt (neduocion r enviranmemtal rmpacts) cofnoared to the worst route selected. 

This route selectively produces one halide and one alcohol. 

Another important parameter that has to be deeply considered is the pH. It is well known the role of pH on silica chemistry it affects dissolution and polymerization rate, gel or precipitate formation and the textural properties of the final silica (11). Also for surfactant micelle or cluster templated syntheses of silica-aluminas, the effect of pH on porosity remains relevant and it is strongly influenced by the kind of material and by the synthesis route selected for its preparation. 

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