RME

The reactivity of the halogens decreases m the order F2 > CI2 > Br2 > I2 Fluo rme is an extremely aggressive oxidizing agent and its reaction with alkanes is strongly exothermic and difficult to control Direct fluonnation of alkanes requires special equip ment and techniques is not a reaction of general applicability and will not be discussed further... 

Eig. 34. Diagram of the Rheometric Melt Elongational Rheometer (RME) for elongational viscosity measurements on polymer melts. 

Carbon-nitrogen multiple bonds in fluorinated imines and nitriles react with halogen fluoride reagents Imines provide 7V-chloroamine.s on reaction with chlo rme fluoride [62, 121, 122, 123] (equations 23 and 24) or with cesium fluoride and chlorine [124] and A -bromoammes on reaction with cesium fluoride and bromine (equation 24)... 

There are two steps required to detennine whetlier risks or haaird indices for two or more pathways should be combined for a single exposed individual or group of individuals. The first is to identify reasonable exposure pathway combinations. The second is to examine whcUier it is likely that the same individiuils would consistently face the "reasonable ma.ximum exposure (RME) by more than one pathway. 

In some situations, it may be appropriate to combine one pathway s RME risks with other pathway s risk estimates diat liave been derived from more typical exposure parameter values. In this way, resulting estimates of combined pathway risks may better relate to RME conditions. 

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

If a balanced chemical reaction involves more than one reagent, one of them will be the reference limiting reagent which will define the scale of the entire reaction. The numerator in the stoichiometric factor term takes into account the sum of the masses of all excess reagents used as appropriate. For any balanced chemical reaction in which all byproducts are identified, equation (4.1) maybe used to determine RME under a variety of scenarios. 

Expressions for RME for any chemical reaction under various scenarios. 

The quantities RME and (Sheldon environmental impact factor or -factor based on mass) ° are related by a simple expression given by equation (4.4) which allows easy calculation of either parameter once one of them is known. It is often simpler to determine Em first and then to use equation (4.4) to calculate RME. The derivation of equation (4.4) is linked to that of equation (4.1) and is also given in Appendix B. 

One can see that the forms of equations (4.4) and (4.5) are identical. It is clear that RME (AE) and Em (Emw) describe material efficiency from different points of view, the former with respect to the target product and the latter with respect to the waste products. Figure 4.1 shows the interconnections between the key material green metrics presented above. 

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... 

The five parameters in equation (4.1) (RME, AE, e, 1/8F and MRP) can be displayed graphically in the form of a radial pentagon as shown in Figure 4.3 depicting a materials usage footprint so that it can be recognized at once which of the four factors on the... 

Figure 4.4 shows the resultant radial pentagon for the Grignard reaction corresponding to the numerical results given in Figure 4.2. From this visual representation it is clear that the low overall RME is due to a modest AE of 60%, the use of 61% excess reagents, and a...

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

Figure 4.4 Radial pentagon representing RME values for the synthesis of diphenylmethanol using the Grignard methodology under various scenarios. See Scheme 4.1 for balanced chemical reaction.

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... 

We now examine some special reaction types which yield more than one useful product to illustrate how the general expression for RME maybe used. 

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