Disclaimer and Assumptions Made in E-Factor Calculations

The E-factors tabulated in Table 23.3 are by no means intended as authoritative figures to judge which of these guanidine catalysts were prepared with less waste. The reasons are as follows  

1) There is alvt ys a potential for the synthesis route to be improved and routes provided in the literature are not necessarily optimised. Some routes could significantly be improved if optimised to be more relevant to green chemistiy. Therefore, it is perhaps inappropriate to compare the E-factor of routes for different catalysts. 

2) It is important to note that most of the reported guanidine catalysts have unique reactivity, therefore the choice of catalyst may be largely determined by the capability afforded by a particular guanidine. 

3) It is difficult to choose the appropriate starting material for calculation of cumulative E-factor such that a fair comparison could be made amongst various guanidines and we do not claim that our choice of starting material is the most appropriate. 

4) We assume that the solvent used is not recovered this is unlikely to be true in an industrial setting where solvent recovery is usually 50-80%. However, it should be noted that solvents and reagents used in work-up procedures (extraction, column chromatography and drying) which constitute a significant amount of the total are not included in our calculations of the E-factor. 

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