Syntheses, chemical steps defined

It is instructive to compare the atom economies of the two pathways. Atom economy is a measure of the efficiency of a chemical process, defined in percentage terms as x (formula wt. of atoms utilized)/(formula wt. of all reactants). For the old six-step ibuprofen synthesis the atom economy was only 40% (with MeC02H, EtOH, NaCl, Et0C02H, 2H2O and NH3 as waste). This is dramatically improved to 77% for the new three-step route with only MeC02H as a by-product from the first step. Recovery and use of this increases the atom economy to 99%. Additionally, the catalytic amounts of HF and Pd complex used in the BHC process are recovered and reused, whereas stoichiometric quantities of AICI3 hydrate were produced as waste by the old route. 

The solution came, in part, by the application of biotransformations. These can be defined as biological processes that modify organic compounds via simple chemical reactions (oxidations, reductions) by means of enzymes contained in microbial, plant, or even animal cells. The aim is usually a one-step reaction to a recoverable product in a sequence of steps in which the majority of conversions are chemical steps (i.e., synthesis). In fermentation processes the whole sequence of reactions is carried out by microorganisms, be it a carbohydrate breakdown to alcohol (or other solvents), the production of antibiotics, or even enzymes. 

Each step in dendrimer synthesis occurs independent of the other steps therefore, a dendrimer can take on the characteristics defined by the chemical properties of the monomers used to construct it. Dendrimers thus can have almost limitless properties depending on the methods and materials used for their synthesis. Characteristics can include hydrophilic or hydrophobic regions, the presence of functional groups or reactive groups, metal chelating properties, core/shell dissimilarity, electrical conductivity, hemispherical divergence, biospecific affinity, photoactivity, or the dendrimers can be selectively cleavable at particular points within their structure. 

In this work, a detailed kinetic model for the Fischer-Tropsch synthesis (FTS) has been developed. Based on the analysis of the literature data concerning the FT reaction mechanism and on the results we obtained from chemical enrichment experiments, we have first defined a detailed FT mechanism for a cobalt-based catalyst, explaining the synthesis of each product through the evolution of adsorbed reaction intermediates. Moreover, appropriate rate laws have been attributed to each reaction step and the resulting kinetic scheme fitted to a comprehensive set of FT data describing the effect of process conditions on catalyst activity and selectivity in the range of process conditions typical of industrial operations. 

Organic electrochemistry fulfills favorably the requirements defined for a good synthesis (see Sect. 3.2). The Umpolung of reactivity by FT saves steps because it allows a one-step coupling of two donors or two acceptors. In comparable chemical conversions, two or more steps are necessary for that purpose. The selectivity... 

By well defined we mean that all the steps of the catalyst synthesis have been followed stepwise (physisorption and chemisorption of the starting organometallic, chemical transformation on the surface, etc.) by an adequate variety of chemical and physical tools at the disposal of chemists such as the mass balance of any reaction occurring during adsorption, in situ IR, NMR, EXAFS, UV-visible, chemical analysis, and so on. 

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