Design of a synthesis

In order to continue the design of a synthesis, 2 is now analysed further by the disconnection strategy for aliphatic bonds. WODCA detects two strategic bonds which are rated 100 and 67, respectively. The disconnection of the bond with the highest rating forms two precursor compounds, 3 and 4 (Figure 10,3-52),... 

The disconnection approach may be used for both linear and convergent syntheses (see section 10.2). However, in both cases the design of a synthesis using the approach must take into account the following ... 

The design of a synthesis for a complex molecule follows the same approach that was first introduced in Section 10.15, and amplified in Sections 11.14, 17.14, 18.11, and 20.11, that is, working backward from the target compound or retrosynthetic analysis. Recall that this process involves envisioning a reaction that can be used to prepare the target compound from a simpler compound. This simpler compound then becomes the target for the next step, and this process is continued until a commercially available compound is reached. 

The design of a synthesis is based on a careful analysis of the structure sought. This process, termed retrosynthetic analysis by Corey, who is responsible for its formalization, can be performed manually or in a computer-aided fashion (1). It involves consideration of all potential bond breakings—thus, retiosynthesis—of the target. Each is evaluated in terms of the probability of success, based on known reactions, of the reverse, synthetic transformation. In its more sophisticated forms, the computer program will provide an estimate of the probability of success of the proposed transformation, as well as relevant literature citations. 

Individual polyethers exhibit varying specificities for cations. Some polyethers have found appHcation as components in ion-selective electrodes for use in clinical medicine or in laboratory studies involving transport studies or measurement of transmembrane electrical potential (4). The methyl ester of monensin [28636-21 -7] i2ls been incorporated into a membrane sHde assembly used for the assay of semm sodium (see Biosensors) (5). Studies directed toward the design of a lithium selective electrode resulted in the synthesis of a derivative of monensin lactone that is highly specific for lithium (6). 

Optimal design of ammonia synthesis by differential equation solution and a numerical gradient search... 

Figure 8. Designs of ammonia synthesis oonverters (a) Prinoipie of the autothermai ammonia synthesis reaotor (b) Radiai fiow oonverter with oapaoities of 1,800 tpd (o) Horizontai three-bed oonverter and detaii of the oataiyst oartridge. Source Wales, M. S., Chemioai Prooess Equipment, Seieotion and Design, Butterworth Series in Chemical Engineering, 1988.)...

Although very efficient, the broad application of the direct preparation is restricted due to the limited number of pure starting enantiomers. The design of a multistep process that includes asymmetric synthesis is cumbersome and the development costs may be quite high. This approach is likely best suited for the multi-ton scale production of commodity enantiomers such as the drugs ibuprofen, naproxen, atenolol, and albuterol. However, even the best asymmetric syntheses do not lead to products in an enantiomerically pure state (100 % enantiomeric excess). Typically, the product is enriched to a certain degree with one enantiomer. Therefore, an additional purification step may be needed to achieve the required enantiopurity. 

Design of a linker for both ligands and synthesis of this compound. 

Particular care is taken in the design of a model to define it in such a way that it can be converted to a procedure characterized by short computation times. This is deemed essential for the evaluation of the large number of molecules which can be generated during a synthesis study or in reaction prediction. Since studies on molecules with up to 70 atoms are quite often performed with EROS, rapid evaluations of many large molecules has to be realistic. 

A combination of organometallic procedures has been used in the design of a simple, efficient synthesis of 2-alkylindoles from o-bromoanilines.76 The arylamines are converted in reactions with 73-allylnickel dimers77 into 2-allylarylamines (36, Scheme 48) which can be cyclized in a separate step... 

The most difficult problem to solve in the design of a Fischer-Tropsch reactor is its very high exothermicity combined with a high sensitivity of product selectivity to temperature. On an industrial scale, multitubular and bubble column reactors have been widely accepted for this highly exothermic reaction.6 In case of a fixed bed reactor, it is desirable that the catalyst particles are in the millimeter size range to avoid excessive pressure drops. During Fischer-Tropsch synthesis the catalyst pores are filled with liquid FT products (mainly waxes) that may result in a fundamental decrease of the reaction rate caused by pore diffusion processes. Post et al. showed that for catalyst particle diameters in excess of only about 1 mm, the catalyst activity is seriously limited by intraparticle diffusion in both iron and cobalt catalysts.1... 

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