Synthesis atom economy

Thus, the goal of green chemistry is to consider all of the atoms used in a synthesis. Atom economy, more so than percent yield, is the best way to do this. 

The need to implement green chemistry principles (e.g., safer solvents, less hazardous chemical synthesis, atom economy, and catalysis) is a driving force toward the avoidance of the use of toxic organic solvents. A solvent-free or solid-state reaction obviously reduces pollution and reduces handling costs due to simplification of experimental procedure and workup technique and savings on labor. However, interest in the environmental control of chemical processes has increased remarkably in the last three decades as a response to public concern about the use of hazardous chemicals. Therefore, to improve the effectiveness of this method in preventing chemical waste, it is important to investigate its optimal conditions. 

A synthetically powerful method, an approach based on cycloaddition chemistry, allows one to assemble the pyridine ring in one step. Not only is this method efficient, atom economy, but also its convergency allows for the preparation for highly substituted systems in which one can, in principle, control all five positions on the pyridine ring. A versatile example of this methodology is the Boger reaction. It has been applied to the synthesis of a very diverse set of targets. 

From the standpoints of both cost and atom economy, water is the ideal nucleophile for synthesis of enantioenriched C2-symmetric 1,2-diols from meso-epoxides. 

Other than energy considerations, on which there is little comparative data, the most important green role for photochemistry is in improving atom economy. Although only a preliminary research result, an excellent example of this is the avoidance of the need for stoichiometric amounts of Lewis acid catalysts in the synthesis of some acylated aromatic compounds. Benzoquinone can be reacted with an aldehyde under a sunlamp to yield an acylhydroquinone in up to 88% yield. The alternative procedure would involve reaction of an acyl chloride with hydroquinone and a... 

Condensations Highly atom economical since small molecules of water or alcohol are liberated Atom economy increases as the molecular weights of the combining fragments increases For cyclization reactions such as the Dieckmann condensation and the synthesis of cyclic ethers from straight chain diols the atom economy increases with increasing ring size... 

Table 4.29 summarizes the metrics for 4 plans to the antibiotic thienamycin and Figure 4.62 shows the corresponding synthesis map with starting materials used. The two Melillo and Reider variants by Merck co-workers are the better performers however each plan has certain attributes that are not found in the other. The slightly shorter Reider plan has a higher overall reaction yield though it has a similar atom economy and overall kernel RME to the Melillo plan. Further optimization would be required to result in all optimum metrics occurring in the same plan. 

Uj+i ordinate of (j + l)th reactant input in synthesis plan AE atom economy fi asymmetry (skewness) parameter... 

Eissen, M., Mazur, R., Quebbemann, H.G., Pennemann, K.H. (2004) Atom Economy and Yield of Synthesis Sequences. Plelvetica Chimica Acta, 87, 524-535. 

Trost, B.M. (1995) Atom Economy. A Challenge for Organic Synthesis - Homogeneous Catalysis Leads the Way. Angewandte Chemie International Edition, 34, 259-281. 

Due to its marked atom economy, the intramolecular hydroamination of alkenes represents an attractive process for the catalytic synthesis of nitrogen-containing organic compounds. Moreover, the nitrogen heterocycles obtained by hydroamination/cyclisation processes are frequently found in numerous pharmacologically active products. The pioneering work in this area was reported by Marks et al. who have used lanthanocenes to perform hydroamination/cyclisation reactions in 1992. These reactions can be performed in an intermolecular fashion and transition metals are by far the more efficient catalysts for promotion of these transformations via activation of the... 

Amination of aromatic nitro compounds is a very important process in both industry and laboratory. A simple synthesis of 4-aminodiphenyl amine (4-ADPA) has been achieved by utilizing a nucleophilic aromatic substitution. 4-ADPA is a key intermediate in the rubber chemical family of antioxidants. By means of a nucleophibc attack of the anilide anion on a nitrobenzene, a o-complex is formed first, which is then converted into 4-nitrosodiphenylamine and 4-nitrodiphenylamine by intra- and intermolecular oxidation. Catalytic hydrogenation finally affords 4-ADPA. Azobenzene, which is formed as a by-product, can be hydrogenated to aniline and thus recycled into the process. Switching this new atom-economy route allows for a dramatic reduction of chemical waste (Scheme 9.9).73 The United States Environmental Protection Agency gave the Green Chemistry Award for this process in 1998.74... 

Industry, in fact, has a major interest in these diesters as building blocks for nylon 6,6 and nylon 7,7 in the production of polyesters and polyamides. However, their present synthesis raises an environmental concern. For instance, the oxidation of cyclohexanone by nitric acid (for the preparation of adipic acid), accounts for more than 10% of the total yearly release of N2O, which is among the main gases responsible for the greenhouse effect. The reaction of Scheme 4.14 represents an eco-friendly alternative synthesis of a,(i)-diesters which uses green reagents and, relevantly, has a 100% atom economy. The overall process is mechanistically described as a retro-Claisen condensation. 

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