Atom Economy

Topics: Chemistry, Chemical reaction, Stoichiometry Pages: 12 (3079 words) Published: July 11, 2013
Green Chemistry Institute Atom Economy Page 1 American Chemical Society ---------------------------------------------------------------------------------------------------------------------

CLEANING UP WITH ATOM ECONOMY
By Kathryn E. Parent, k_parent@acs.org

Introduction
Cleaning up the environment and, more importantly, preventing pollution are important issues in today’s world. The theme for the 2002 National Chemistry Week is “Chemistry Keeps Us Clean.” While the chemical industry is traditionally viewed more as a cause than a solution to pollution, chemistry does offer unique solutions in the area of waste prevention. One of the most fundamental of these solutions is the application of the green chemistry principle of atom economy to chemical reactions. Atom economy moves the practice of minimizing waste to the molecular level. Traditionally, chemists have focused on maximizing yield, minimizing the number of steps or synthesizing a completely unique chemical. Green chemistry and atom economy introduce a new goal into reaction chemistry: designing reactions so that the atoms present in the starting materials end up in the product rather than in the wastestream. This concept provides a framework for evaluating different chemistries, and an ideal to strive for in new reaction chemistry (1,2,3).

Green Chemistry Principle: Atom Economy
Atom economy means maximizing the incorporation of material from the starting materials or reagents into the final product. It is essentially pollution prevention at the molecular level. For example, a chemist practicing atom economy would choose to synthesize a needed product by putting together basic building blocks, rather than by breaking down a much larger starting material and discarding most of it as waste. Atom economy is an important development beyond the traditionally taught concept of percent yield. Barry Trost, from Stanford University, published the concept of atom economy in Science in 1991 (4). In 1998 he received the Presidential Green Chemistry Challenge Award (5) for his work. At the award ceremony, Paul Anderson (1997 ACS President) commented, “By introducing the concept of ‘atom economy,’ Dr. Trost has begun to change the way in which chemists measure the efficiency of the reactions they design.” Atom economy answers the basic question, “How much of what you put into your pot ends up in your product?” (6). To meet the challenge of atom

Green Chemistry Institute Atom Economy Page 2 American Chemical Society --------------------------------------------------------------------------------------------------------------------economy, Trost has developed a number of palladium and ruthenium catalysts. These catalysts enable chemical synthesis to proceed by simple addition reactions (7).

Associated Chemistry Topics
law of conservation of matter chemical reactions stoichiometry percent yield

Vocabulary
Atom Economy – 1) The mass of desired product divided by the total mass of all reagents, times 100

Percent Atom Economy

=

Mass of Desired Product Total Mass of all Reagents

x 100

2) The mass of desired product divided by the total mass of all products and byproducts produced, times 100 3) A measure of the efficiency of a reaction (8) Green Chemistry – 1) Designing chemical products and processes to reduce or eliminate the use or generation of hazardous materials 2) Using chemistry for pollution prevention 3) Benign by design, sustainable chemistry Molecular Weight – mass of one mole of a compound (units of grams per mole) Percent Yield – actual yield divided by theoretical yield times 100 Theoretical Yield – the maximum amount of product that can be produced from the quantities of reactants used; the amount of a given product formed when the limiting reactant is completely consumed Saponification – the decomposition of triglycerides with aqueous sodium hydroxide Stoichiometry – application of the laws of definite proportions and conservation of...

References: (1) Anastas, P. T,; Warner, J. C. Green Chemistry: Theory and Practice, Oxford University Press: Oxford, UK, 1998. (2) Cann, M. C.; Connelly, M. E. Real World Cases in Green Chemistry, American Chemical Society: Washington, DC, 2000. See also the University of Scranton’s Greening Across the Curriculum Web Site, http://academic.scranton.edu/faculty/CANNM1/organicmodule.html (3) Ryan, M. A.; Tinnesand, M., Eds. Introduction to Green Chemistry, Washington, DC: American Chemical Society, 2002. (4) Trost, B. M. Science 1991, 254, 1471-1477. (5) The Presidential Green Chemistry Challenge is an award program sponsored jointly by the Environmental Protection Agency (Office of Pollution Prevention and Toxics) and the American Chemical Society—Green Chemistry Institute. Introduced in 1995, it is the only program to provide national recognition for green chemistry. The program offers five awards to academic researchers, industry, and government laboratories for innovations in the following categories: 1) academic, 2) small business, 3) alternative reaction conditions, 4) alternative synthesis, and 5) design of safer chemicals. For information about the Presidential Green Chemistry Challenge, refer to the Web Site: http://www.epa.gov/greenchemistry/presgcc.html (6) Trost, B. M. In The Presidential Green Chemistry Challenge Awards Program: Summary of the 1998 Award Entries and Recipients; EPA744-R-98-001, U.S. Environmental Protection Agency, Office of Pollution Prevention and Toxics: Washington, DC, 1998; p 2. (7) Trost, B. M. Acc. Chem. Res. 2002, 35, 695-705. (8) For a powerpoint presentation of atom efficiency, with excellent examples, see the Green Chemistry Network Web Site, http://www.chemsoc.org/pdf/gcn/atomeff.ppt (9) Witzel, J. Eric. J. Chem. Educ. 2002, 79, 352A-352B. (10) Trost, B. M. Acc. Chem. Res. 2002, 35, 695-705.
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