Atom efficiency/economy

However, one category of selectivity is largely ignored by organic chemists the atom selectivity , or what is variously called atom economy (Trost, 1991, 1995), atom efficiency, or atom utilization solvents (Sheldon, 1992, 1992a, 1993, 1994, 1996, 1997, 1997a). The complete disregard of this parameter is the root cause of the waste problem in fine chemicals manufacture. 

Some aspects of synthetic chemistry have changed in response to environmental needs. For example, in the pharmaceutical industry the classical methods produce, on the average, about nine times as much disposable waste as desired product. This has led to the demand for procedures that have atom efficiency, in which all the atoms of the reacting compounds appear in the product. Thus (as discussed earlier) the demand for atom economy offers additional opportunities for creative invention of transformations. 

Atom-atom mapping, 10 333 Atom economy, 12 803-804 Atom efficiency, 12 810-811 Atomic absorption (AA), 25 370 Atomic absorption spectroscopy, 15 348 of archaeological materials, 5 742 determining trace mercury using, 16 44 5... 

The atom utilization [13-18], atom efficiency or atom economy concept, first introduced by Trost [21, 22], is an extremely useful tool for rapid evaluation of the amounts of waste that will be generated by alternative processes. It is calculated by dividing the molecular weight of the product by the sum total of the molecular weights of all substances formed in the stoichiometric equation for the reaction involved. For example, the atom efficiencies of stoichiometric (Cr03) vs. catalytic (02) oxidation of a secondary alcohol to the corresponding ketone are compared in Fig. 1.1. 

What is green chemistry (5) What is atom economy (6) How can atom efficiency be applied (7)... 

Nowadays, a chemical process for the production of a desired product has to be evaluated considering its conversion, chemical yield and selectivity, but also its atom efficiency, according to the atom economy principle established by Trost in 1991. ... 

Atom efficiency the percentage yield (molar flow of the desired product divided by the molar flow of the limiting reactant, taking into account the stoichiometry of the reaction) multiplied by the atom economy. It could be used to replace yield and A E. Eor example, AE could be 100% and yield 5%, making this a not very green reaction. 

The formation of C-C bonds is of key importance in organic synthesis. An important catalytic process for generating C-C bonds is provided by carbonylation. Most carbonylation reactions have a good atom economy, because most reagent atoms are transferred to the product. Therefore, there are some applications of carbonylation processes in fine chemistry, too. For example, the analgesic ibuprofen is produced by Hoechst-Celanese by carbonylation of a substituted alcohol with 100% atom efficiency according to Eq. (8-20) [7] ... 

Cyanohydrins are usually prepared from carbonyl compounds and a cyanide source. Initially performed with volatile and very toxic hydrogen cyanide, the reaction is now carried out with safer cyanide agents, such as acetone cyanohydrin, acyl cyanides, cyanoformates or the most used trimethylsilyl cyanide. In terms of atom economy, this reaction is 100% atom efficient and is widely used despite the toxicity of the reagents. The asymmetric reaction can now be efficiently catalysed by a variety of chiral Lewis acids, and a recent review presents in detail the work realised in this field, with a large description of titanium-based catal)dic systems. 

The atom economy is an important concept of the green chemistry philosophy proposed by Trost (3). This concept is that reactions should be designed to be atom efficient for economic and environmental reasons. Therefore, as many of the atoms in the reactants as possible should be included in the products. For evaluation of the concept of atom economy, it is necessary to consider atom efficiency. The atom efficiency of a reaction is defined as the ratio of the molecular weight of the desired product to the sum of the molecular weights of all of the materials produced in the process. For example, in the reaction that converts... 

Green chemistry has introduced several new terms and new research frontiers, including "eco-efficiency," "sustainable chemistry," "atom efficiency or economy," "process intensification and integration," "inherent safety," "product life-cycle analysis," "ionic liquids," "alternate feedstock," and "renewable energy sources."... 

As much as it is a key in achieving economic objectives, catalysis is also a powerful tool in realizing the goals of green chemistry. Innovation in the field of catalysis is driven by both profit motives and efforts to make more eco-efficient processes. Most often profits are markedly improved with the development of green processes. An important concept of green chemistry that can be addressed by the use of catalysis is atom-efficiency, also known as atom-economy. 

Atom economy for the n-butane route is 57.6% and 44.4% for the benzene route. Thus, n-butane is preferred over benzene as a raw material for production of maleic anhydride. Choosing an atom efficient raw material is the first step in designing an environment-friendly chemical process. 

Synthesis II An alternative route with greater atom economy starts with 4-isobutylacetophenone. (below) Although synthesis II is more atom-efficient than synthesis I, it uses a cyano group, neither atom of which appears in the final product. 

Atom economy (atom efficiency) defines the conversion efficacy of a chemical operation in terms of all atoms concerned (desired products produced). Atom economy can be written as Atom economy = [(molecular mass of all desired products)/(molecular mass of all reactants)] X100... 

Overall, the imidazolidinone process achieves 6.8 % atom efficiency, consistent with the extensive use of blocking groups. This feature is not present in the oxazolidinone route, which has an atom economy of 48.5%, an indicator of a much higher synthetic efficiency. 

There are two ways to estimate the environmental impact of a given manufacturing process. The methods are interrelated but in one case the atom efficiency (AE) or the atom economy of the process is calculated. In the other method, we calculate a parameter called the E factor. In a given process if the molecular weight of the desired product is P and the total molecular weight of all the products is P, then AE and the theoretical E factor (E) are given by Equation 1.6.1.1. 

An important aspect of green chemistry involves atom economy. If we consider the oxidation of PhCH(OH)CHj to PhC(=0)CH3 using chromium trioxide, the atom efficiency, the proportion of the product that is actually something we want, is 42 % (Equations 25.4 and 25.5). If the oxidation could be done using molecular oxygen as the oxidant and a catalyst, then this rises to 86 % (Equations 25.6 and 25.7). In both cases, this is only a theoretical figure to get a more practical... 

This is a very low atom efficiency, reflecting the large mass of undesired product that is formed, and the strong desire for carbon capture as an opportunity to minimize air pollution. In addition, the atom economy concept does not take into account the use of energy, auxiliaries, or catalysts and the toxicity of the waste, and in this case, the reaction is impacted by the high temperature required. 

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. 

---