Improvement in Waste Reduction

The more efficient G2 plan has more reaction steps and stages, uses more input materials, and has a lower overall atom economy. It also utilizes a higher molecular weight fraction of sacrificial reagents. These apparent counterintuitive results are rationalized when one examines the high reaction yield efficiencies of each step compared with the G1 plan. The main bottlenecks in the G1 plan are a 20% reaction yield for an intramolecular Friedel-Crafts alkylation in step 7, 

By contrast the lowest yield reaction in the G2 plan is a Wittig coupling occurring in 65% yield. 

This mismatch in metrics parameters is a clear sign, despite the great improvement in waste reduction, that true optimization has still not yet been achieved since all parameters are not optimally gravitating in the same plan. 

FIGURE 11.16 Time profile of E-total for various syntheses of (+)-sertaline hydrochloride. 

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