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Atom Economy in Drug Synthesis is a Playground of Functional Groups

Kartik R. Patel, Dr. Dhrubo Jyoti Sen and Viraj P. Jatakiya

Like most other people, chemists are concerned with environmental pollution. This concern has given rise to a field called green chemistry, which involves the design of chemical products and processes that minimize environmental problems. One of the principles, called atom economy, involves—among other things— designing reactions in such a way that the quantity of reactants that end up in the desired final product is the maximum possible. We can define the percent atom economy (% AE) of a reaction by the formula. Atom economy also must consider substances such as solvents, separation agents and drying agents that are used in the process but are not directly part of the chemical reaction. Using a green chemistry approach, chemists attempt to either reduce the amount of or eliminate completely as many of these substances as possible. Those that cannot be eliminated are reused or recycled when possible. Atom economy (atom efficiency) describes the conversion efficiency of a chemical process in terms of all atoms involved (desired products produced). In an ideal chemical process, the amount of starting materials or reactants equals the amount of all products generated and no atom is wasted. Recent developments like high raw material (such as petrochemicals) costs and increased sensitivity to environmental concerns have made atom economical approaches more popular. Atom economy is an important concept of green chemistry philosophy and one of the most widely used ways to measure the "greenness" of a process or synthesis. Atom economy can be written as: % atom economy = (Molecular weight of desired product ÷ Molecular weight of all reactants) × 100 Atom economy can be poor even when chemical yield is near 100%. Atom economy can also be adjusted if a pendant group is recoverable. However, if this can be avoided it is more desirable, as recovery processes will never be 100%. Atom economy can be improved upon by careful selection of starting materials and a catalyst system. Atom economy is just one way to evaluate a chemical process. Other criteria can include energy consumption, pollutants released and price. Poor atom economy is common in fine chemicals or pharmaceuticals synthesis and especially in research, where the aim to readily and reliably produce a wide range of complex compounds leads to the use of versatile and dependable, but poorly atom-economical reactions. It is fundamental in chemical reactions of the form A+B→C+D that two products are necessarily generated though product C may have been the desired one. That being the case, D is considered a byproduct. As it is a significant goal of green chemistry to maximize the efficiency of the reactants and minimize the production of waste, D must either be found to have use, be eliminated or be as insignificant and innocuous as possible. With the new equation of the form A+B→C, the first step in making chemical manufacturing more efficient is the use of reactions that resemble simple addition reactions with the only other additions being catalytic materials. Functional groups of all the starting substances have been converted into another group by synthetic step by green chemistry reaction followed by atom economy