Atom economy equation

One of the fundamental and most important principles of Green Chemistry is that of atom economy. This essentially is a measure of how many atoms of reactants end up in the final product and how many end up in byproducts or waste. The percentage atom economy can be calculated as 100 times the relative molecular mass (RMM) of all atoms used to make wanted product divided by the RMM of all reactants. Box 1.2. The real benefit of atom economy is that it can be calculated at the reaction planning stage from a balanced reaction equation. Taking the following theoretical reaction ... 

There are a number of past and present commercial routes to phenol using benzene as a feed stock. Outline two such processes, writing balanced equations for the reactions involved. Compare the two routes in terms of atom economy. 

Review a recent synthetic reaction you have carried out in the laboratory. Write a balanced equation for the reaction(s) and calculate the atom economy. From your experimental results calculate the Yield, E-factor and Effective Mass Yield (ignoring any water used). Identify ways in which this reaction could be made greener. 

It is understood that the ortho and meta products form part of the waste produced. In determining AE, the balanced chemical equation is written with a generalized structure for the product indicating all possible isomers and since the molecular weights of all isomers are identical equation (4.2) is used without change. In the above example, the atom economy for the production of para, meta or ortho products is the same. 

The isomerization of allylic alcohols provides an enol (or enolate) intermediate, which tautomerizes to afford the saturated carbonyl compound (Equation (8)). The isomerization of allylic alcohols to saturated carbonyl compounds is a useful synthetic process with high atom economy, which eliminates conventional two-step sequential oxidation and reduction.25,26 A catalytic one-step transformation, which is equivalent to an internal reduction/oxidation process, is a conceptually attractive strategy due to easy access to allylic alcohols.27-29 A variety of transition metal complexes have been employed for the isomerization of allylic alcohols, as shown below. 

As noted above, a knowledge of the stoichiometric equation allows one to predict the theoretical minimum amount of waste that can be expected. This led to the concept of atom economy [8] or atom utilization [9] to quickly assess the environmental acceptabihty of alternatives to a particular product before any experiment is performed. It is a theoretical number, that is, it assumes a chemical yield of 100% and exactly stoichiometric amounts and disregards substances which do not appear in the stoichiometric equation. 

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. 

Barry Trost of Stanford University published the first formal green metric in 1991 in Science. Trost s idea, atom economy, measures the percentage ratio of the total mass of the products to starting materials (Equation 13.2).26... 

Shortly after Trost introduced the idea of atom economy, Roger Sheldon of Delft University of Technology in the Netherlands reported another green metric called E-factor.30 31 E-Factor is the ratio of the mass of the total waste from a process to the mass of the product generated in that same process (Equation 13.5). 

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. 

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. 

This discrepancy therefore necessitates the introduction of the concept of atom economy. Atom economy is an assessment in which one looks at all the reactants to measure the degree of their incorporation in the product. Thus, if all the reactants are completely incorporated into the product, the synthetic pathway is said to be 100% atom economical because it will not generate waste. The atom economy is calculated with the following equation (seeTrost, 1991) ... 

Integration of green chemistry principles into pre-lab and post-lab questions is another easy and effective inclusion method. The synthesis of aspirin is a common first-year lab procedure. One of the fundamental principles of green chemistry is atom economy. A possible pre-lab question might be to have the students calculate the percent atom economy of the synthesis using the following equation ... 

This relatively simple calculation can then lead to questions about whether the atom economy calculated from the balanced equation is truly achievable, and if not, how that relates to the issues of waste. 

Among all of the homogeneous processes catalyzed by transition metals, hydro-formylation stands out in three respects. It is the oldest process still in use today, it is responsible for producing the largest amount of material resulting from a homogeneous transition metal-catalyzed reaction,9 and it can be considered a green process because it proceeds with almost 100% atom economy. The hydroformylation reaction was outlined already in equation 9.5. 

The atom economy (AE, as percentage) was calculated considering the mass-balance of a process related to its stoichiometric equation, that is, the percentage of atoms of the reagent that end up in the product ... 

By and large, selectivity was equated with efficiency. However, just a little further thought makes us realize that we are missing one key aspect of efficiency by focusing only on selectivity, that is, by ignoring an obvious but neglected aspect, which is, simply put, how much of what you put into your pot ends up in your product In 1991, this fundamental and critical issue was explicitly recognized and referred to as atom economy [3], In 1992, the Efactor was introduced, which also... 

Application of this catalyst system to propargyl alcohols provides a, 3-unsaturated aldehydes (Equation 1.17) and ketones (Equation 1.18) [18]. The ease of accessibility of the substrates by simple addition of terminal alkynes to aldehydes followed by this redox isomerization constitutes a highly chemoselective and atom economic strategy to these unsaturated carbonyl compounds. The chemoselectivity problems of the direct aldol condensation and the poor atom economy of olefination methods make this new strategy the most efficient and reliable approach to these units. 

We had established in previous catalytic reactions involving complex 24 that this precatalyst was activated by the removal of the cod (1,5-cyclooctadiene) from the ruthenium by its reaction with the alkyne substrate via a [2 + 2 + 2] cydization as illustrated in Equation 1.64 [57]. Thus, not only does this reaction constitute an activation of the Ru complex 24 by reacting off the cod, it also serves as a novel atom economic reaction in its own right. Both internal and terminal alkynes participate. The overall atom economy of this process is outstanding since cod itself is simply available by the nickel-catalyzed dimerization of butadiene. Thus, the tricyclic product is available by the simple addition to two molecules of butadiene and an alkyne with anything else only needed catalytically. 

Adding a catalytic amount of an alkyne to the reaction in Equation 1.63 indeed enhanced the yield dramatically. The quantitative yield for the activation step obtained using 3-hexyn-l-ol made this alkyne the one of choice as the activator for the allene addition. Taking advantage of this atom economic synthesis of 1,3-dienes by employing the [4 + 2] cydoaddition then allows complex cyclic entities to be available with high atom economy. 

The synthesis of adipic acid in the laboratory can be carried out by the oxidation of cyclohexene with potassium permanganate (Equation 4.6). The E-factor of this reaction is 2.61, which means that for 1kg of adipic acid 2.61kg waste (mainly Mn02 and KOH) is produced. The atom economy is 27.8%, indicating that only 27.8% of the atoms in the reactants will be incorporated into the product. 

A greener method has been developed using hydrogen peroxide as the oxidant, with catalytic amounts of sodium tungstate and a quaternary ammonium phase-transfer catalyst (Equation 4.7) [16]. Since the solvent and the by-product are water, the reaction is indeed much greener (E-factor = 0.49, atom economy 67%). 

The oxidation of primary alcohols with an excess of an oxidizing agent produces carboxylic acids (Equation 4.10). The fc -factor for the oxidation of ethanol to acetaldehyde is 1.74 and the atom economy is only 36.5%. 

I m teaching more the inorganic section and materials, nonetheless I had to revise on some mechanisms, such as polymerization mechanisms. The need to balance chemical equations for the purposes of teaching the atom economy concept forced me to relearn and strengthen my understanding of the fundamentals, particularly for reduction and oxidation-type reactions, where by-products are not often declared in the literature and in textbooks. 

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