Reaction mass efficiency

Reaction mass efficiency (RME) is a metric that was first introduced by Curzons et al. [4] as a means of including the concept of atom economy (AE), while adding yield and the reactant stoichiometry. RME is defined as the percentage of the mass of the reactants that remain in the product. There are two ways to calculate RME. 

Because reaction mass efficiency includes the stoichiometry of a reaction and the yield, it is thought to be a more accurate reflection of the true efficiency of a given chemical reaction. But why would this be the case Experienced chemists know that many reactions require significant molar excesses to drive the reaction to completion. They also are well aware of the fact that poor chemical selectivity in all its forms leads to yields that are considerably less than 100%, especially as molecules become more complex (greater functionality), as is the case when making chiral molecules. 

This means that if we would like to account more accurately for the impacts of a chemical synthesis, we need to be more careful about what we include in our metrics. As is readily apparent to any synthetic organic chemist, reagents and solvents promote reactivity and/or at the very least provide a means for heat and mass transfer that ensures good kinetics and chemical selectivity. Although the E-factor may be a good measure for focusing attention on waste, it ignores the product and what we buy in to make our product, that is, the raw materials. Because it looks at the 

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The general expression for reaction mass efficiency (RME), derived in Appendix B, for any individual chemical reaction is given by... 

A Microsoft Excel (Version 5.0 or higher) spreadsheet template form has been developed which allows the calculation of the complete reaction mass efficiency (RME) according to equation (4.1) and raw material cost (RMC) for any chemical transformation. Lines are numbered and line instructions are embedded in the same manner as a personal income tax form. Green metrics are evaluated to determine the greermess of the experiment in a rigorous quantitative way and to determine the bottom line cost of carrying out the experiment. Formula entries are inserted in appropriate cells to facilitate computation. Any... 

Figure 4.3 Radial pentagon representation of reaction mass efficiency (RME) showing dependence on four independent parameters given in equation (4.1).

Scheme 4.2 shows various organic reaction types and Figure 4.5 shows their corresponding radial pentagons based on actual experimental data. When these diagrams are compared side by side it is possible to visualize at a glance which types of reactions are better atom economical and reaction mass efficient performers than others. In particular, it is possible to pick out which of the four factors in equation (4.1) is responsible for a low or high RME... 

In terms of kernel reaction mass efficiency, the golden threshold for a single step reaction... 

Figure 4.6 (a) Graph showing full domains of atom economy, reaction yield and region where reaction mass efficiency exceeds a threshold value of a for a reaction whose minimum atom economy is zero, (b) Probability that such a reaction can achieve a threshold RME of at least a. i a = 0.61 8, p(a) = 0.08 (8%) as indicated by dotted lines. 

Maximize overall kernel reaction mass efficiency (RME). 

Yield and other mass-related metrics such as atom economy, reaction mass efficiency and mass intensity have been examined by Constable et al with regard to their significance concerning greenness and costs. The importance of using a (product) concentration term, which can be mass intensity or mass index, is additionally emphasized by Laird et al This is in compliance with Winterton, who in his twelve more green chemistry principles demands the establishment of full mass balances. 

Some specific metrics for mass have been found to be useful and are described elsewhere. In addition to reaction mass efficiency described elsewhere and in Chapter 4, a useful metrics is Mass Intensity, defined as ... 

For an example of reaction mass efficiency being used to compare four different processes please see Section 10.4.1. 

Several other metrics include effective mass yield, atom economy, mass intensity, mass productivity, and reaction mass efficiency, which are defined by Equations 3.2-3.6. 

Reaction mass efficiency (RME) extends the idea of atom economy by taking into account a reaction s yield and the use of excess reagents.34 For the reaction A + B + C—>D + E with a desired product D, the formula for percent RME is shown in Equation 13.6. 

Reaction mass efficiency combines key elements of chemistry and process and represents a simple, objective, easily derived and understood metric for use by chemists, process chemists, or chemical engineers. 

Reaction Mass Efficiency (RME) Mass of isolated product (kg) — X 100 Total mass of reactants used in reaction (kg) %... 

There are various other related metrics (i) atom efficiency, (ii) effective mass yield, (iii) carbon efficiency and (iv) reaction mass efficiency ... 

Reaction mass efficiency (RME) the percentage of the mass of the reactants that remains in the product. It takes into account the atom economy, yield and reactant stoichiometry. 

Quantitative evaluation of chemical processes in terms of environmental impact and eco-friendliness has gradually become a topic of great interest since the original introduction of the atom economy (AE) by Trost [1], and the E-factor by Sheldon [2]. Since then, other indexes have been proposed for the green metrics of chemical processes, such as effective mass yield (EMY) [3], reaction mass efficiency (RME) [4] and mass intensity (MI) [5], along with unification efforts [6, 7] and comparisons among these indexes [8]. 

Table 2.1 contains averaged data for 28 different chemistries commonly used in industry. The stoichiometry, yield, atom economy, reaction mass efficiency, mass intensity, and mass productivity are shown for each type of chemistry. 

Reaction yield, a metric universally used by synthetic chemists to evaluate their success, does not include poor reaction mass efficiencies. The correspondingly significant waste of resource (mass or energy) may be an obvious consequence to some, but many do not think about the wasted resource and the expense that this represents from both a direct materials cost and a more comprehensive life cycle costing perspective. 

Because reaction mass efficiency includes all the mass used for a given reaction (whether or not it includes or excludes water), and includes yield, stoichiometry, and atom economy, we believe that this metric is the most helpful metric for chemists to focus their attention on how far from green a given reaction or reaction scheme may be. 

Reaction mass efficiency (%) Mass intensity excluding water (kg kg1) Mass productivity excluding water (%)... 

However, the true greenness of this reaction remained far from being ideal, as the necessity to prepare initially the arylboronic acids (or their derivatives) as nucleophilic starting material and to recycle (or to eliminate) the associated waste thereafter violate several of the TPGC. Hence this not only contradicts the concept of atom economy [35], but also increased Sheldon s environmental impact factor E (E = kgwaste/kgproduct) [36]. As a consequence, this resulted in a decrease in the value of the reaction mass efficiency (RME) forthe Suzuki-Miyaura reaction. The value RME = 1 characterizes an absolutely green reaction, but all reactions with RME >0.618,... 

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