Atom Economy

4 Key excerpts on "Atom Economy"

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  eBook - ePub

  Green Chemistry and Applications

  • Aide Sáenz-Galindo, Adali Facio, Raul Rodriguez-Herrera, Aide Sáenz-Galindo, Adali Facio, Raul Rodriguez-Herrera, Aide Sáenz-Galindo, Adali Oliva Castañeda Facio, Raul Rodriguez-Herrera(Authors)
  • 2020(Publication Date)
  • CRC Press

    (Publisher)

  Chapter 2Atom Economy

  Kunnambeth M. Thulasi1 , Sindhu Thalappan Manikkoth,1 , Manjacheri Kuppadakkath Ranjusha1 , Padinjare Veetil Salija1 Vattakkoval Nisha1 , Shajesh Palantavida2 and Baiju Kizhakkekilikoodayil Vijayan1 *

  1 Department of Chemistry/Nanoscience, Kannur University, Swami Anandha Theertha Campus, Payyannur, Edat P.O., Kerala-670 327, India.

  2 Centre for Nano and Materials Science, Jain University, Jakkasandra, Ramanagaram, Karnataka, India.

  * For Correspondence: [email protected] ; [email protected]

  INTRODUCTION

  The concept of Atom Economy was developed by Barry M. Trost in 1991. Organic synthesis requires multiple reagents, facilitating agents and solvents to obtain the desired product. At the end of the reaction everything except for the desired product and reagents that can be recycled, like solvents and catalysts, will end up as wastes, mostly hazardous wastes. Conceptually, if the desired product contains all the atoms making up the reagents there will be no waste generated. The concept of Atom Economy can be used to identify synthetic methodologies that will retain the maximum number of atoms from the reactants in the final product and thereby reduce wastage. The Atom Economy concept allows quantification of the efficiency of a reaction with respect to the number of atoms transferred from the reactants to the final desired product (Trost, 1995; Trost, 2002). The concept of Atom Economy can be applied to every synthesis and be used to define new pollution prevention benchmarks (Cann and Dickneider, 2004; Song et al., 2004). Atom Economy calculation, broadly presents a measure of the greenness of a chemical reaction. The commonly used indicator for efficiency of a reaction in organic synthesis is the percentage yield, which neglects mass flow (Cann and Dickneider, 2004). A synthetic chemist records the yield of a particular reaction as percentage yield. The percentage yield can be calculated as

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  eBook - ePub

  Biocatalysis for Green Chemistry and Chemical Process Development

  • Junhua (Alex) Tao, Romas Joseph Kazlauskas, Junhua (Alex) Tao, Romas Joseph Kazlauskas(Authors)
  • 2011(Publication Date)
  • Wiley

    (Publisher)

  Raw materials include the source of the energy used in the process, as this leads to waste in the form of carbon dioxide emissions. Green chemistry eliminates waste at source, that is, it is primary pollution prevention rather than waste remediation (end-of-pipe solutions), as described by the first principle of green chemistry: prevention is better than cure. In the last 15 years, the concept of green chemistry has been widely embraced in both industrial and academic circles. One could say that sustainability is our ultimate common goal and green chemistry is a means to achieving it.

  Having defined what Green Chemistry is, we need to be able to compare processes (and products) on the basis of their greenness. We note, however, that there is no absolute greenness; one process is greener than another and, as with beauty, greenness is in the eye of the beholder. Nonetheless, as Lord Kelvin remarked, “to measure is to know,” and appropriate green metrics are a prerequisite for progress toward a meaningful comparison of the greenness of processes.

  4.3 The Metrics of Green Chemistry: Atom Economy and The Environmental Factor

  It is now widely accepted that two useful measures of the potential environmental impact of chemical processes are the E factor [[10–15]], defined as the mass ratio of the waste to the desired product and the Atom Economy [[16, 17]], calculated by dividing the molecular weight of the desired product by the sum of the molecular weights of all the substances produced in the stoichiometric equation.

  A knowledge of the stoichiometric equation enables prediction of, without performing any experiments, the theoretical amount of waste that can be expected. Our experience with the phloroglucinol process (see above) led us to use what we called atom utilization to quickly assess the environmental acceptability of alternative processes to a particular chemical [18]. It was a logical elaboration of the concepts of syn gas utilization [19] and oxygen availability in different oxidants [20]. However, Atom Economy (AE ), introduced by Trost in 1991 [16], has become the widely accepted terminology although atom efficiency (also abbreviated as AE) is also used. In Figure 4.2

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  eBook - ePub

  Contemporary Chemical Approaches for Green and Sustainable Drugs

  • Marianna Torok(Author)
  • 2022(Publication Date)
  • Elsevier

    (Publisher)

  Scheme 9.5 ), which are important compounds in laboratory and industrial settings. The Atom Economy of these reactions is generally low, as there is a stoichiometric amount of coproduct formation.

  The example in Scheme 9.5 shows how the coproduct of the reaction, 1, is also one of the reactants. This allows for the formation of 6 from 2 and 4 while not forming any unusable coproducts. This dramatically increases the atom economy because 1 is effectively acting as a catalyst and is no longer counted toward the Atom Economy.

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  Designing reactions in this manner eliminates the production of unnecessary or unwanted products, thus leading to overall greater Atom Economy and greener processes.

  Scheme 9.5  Direct cycle between coproduct and reactant.

  25

  Table 9.1 shows various synthetic examples and their calculated atom economies. There is a wide range of atom economies present, from 10.51% to 95.56%. Based on the above, a reaction that has an Atom Economy of 95.65% is a greener reaction than the one with an Atom Economy of 10.51%, and although that is mostly correct, there may be exceptions. There is not always a direct connection between the greenness of a reaction and the Atom Economy, thus Atom Economy is only one factor that should be considered in the holistic evaluation of a reaction.

  12

  3.1.2. The E-factor

  The E-factor (environmental factor) was developed by Sheldon as one of the most practical descriptors of the efficiency of a process.

  29

  It is defined as the mass ratio of waste to the target product.

  E-factor is an indicator of the actual amount of waste produced in the process. Waste in this case is defined as everything remaining after the reaction is complete, except for the desired product. Based on that, it takes the chemical yield (and selectivity) into account and includes many aspects during the reaction such as reagents, solvent loss etc. Water is always excluded from the calculation of E-factor

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  eBook - ePub

  Chemistry for Sustainable Technologies

  A Foundation

  • Neil Winterton(Author)
  • 2015(Publication Date)
  • Royal Society of Chemistry

    (Publisher)

  iv and focused attention on atom efficiency in chemical technology, particularly in the pharmaceuticals and fine chemicals sector which, as Sheldon’s E-factor (Section 6.3) estimates suggest, are relatively waste producing.

  For the general reaction eqn (7.15) in which the desired product is C, the atom efficiency is given by eqn (7.16) , i.e. the ratio (usually expressed as a percentage) of the molecular weight (MWt) of the desired product to the sum of molecular weight of the stoichiometric reactants.

  (7.15)

  (7.16)

  If no D is formed, then atom efficiency is 100%.

  More generally, for a sequence of reactions (eqn 7.17 –7.19 ):

  (7.17)

  (7.18)

  (7.19)

  (7.20)

  or overall for the reaction sequence (eqn 7.20 ) leading from A+B to the desired product, J, atom efficiency is given by eqn (7.21) :

  (7.21)

  It is evident that atom efficiencies for multi-step processes, each using additional reactants, are likely to be lower than for single-step processes.

  The importance of the AE concept becomes evident when we compare traditional stoichiometric reactions (e.g. the classical laboratory reduction using sodium borohydride) with the equivalent catalytic reaction operated widely and on a huge scale in the chemical industry. The reduction of acetophenone to 1-phenylethanol may be represented in eqn (7.22) by the simplified overall stoichiometry. (As an exercise, think why this is a simplified

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