In the previous lesson, differences in structure and weighting of HSE criteria in published solvent selection guides were discussed. Initial work carried out by the CHEM21 project included building a methodology to compare the 5 guides available (AZ, GCI-PR, GSK, Pfizer, Sanofi). This methodology, explained in the video, consists of a comparison of the rankings (color codes) of the 51 more represented solvents in these guides. For guides which did not offer a clear ranking (AZ, GSK, GCI-PR), the number of criteria was reduced to three: one for Safety, one for Health, one for Environment. For each guide, three solvent groups of similar size were built around the arithmetical mean, with a classical color code (green, yellow, red). It was thus easy to compare the color code of each solvent in the different guides (Table 1).
|t -BuOH||20||15||15||Preferred||Subst. advisable||TBC|
|Benzyl alcohol||–||11||20||–||Subst. advisable||TBC|
|Ethylene glycol||–||13||21||Usable||Subst. advisable||TBC|
|Ethers||Diethyl ether||27||21||3||Undesirable||Banned||Highly Hazardous|
|Diisopropyl ether||–||–||4||Undesirable||Subst. advisable||Hazardous|
Table 1 is extracted from D. Prat, J. Hayler and A. Wells, A survey of solvent selection guides, Green Chem., 2014, 16, 4546-4551. It is copyright to the Royal Society of Chemistry (RSC) and is reproduced here with their express permission. If you wish to reproduce it elsewhere you must obtain similar permission from the RSC.
This color code comparison gave a clear agreement (large majority) for 34 of the 51 solvents (two thirds of solvents overall). Further discussion permitted the identification of the most hazardous solvents. One third of solvents could not be ranked (named “to be confirmed” in Table 1), thus reflecting the different weighting of criteria in the solvent guides  . The overall list is given in Table 2.
|Recommended||Water, EtOH, i -PrOH, n -BuOH, EtOAc, i -PrOAc, n -BuOAc, anisole, sulfolane.|
|Recommended or problematic?||MeOH, t -BuOH, benzyl alcohol, ethylene glycol, acetone, MEK, MIBK, cyclohexanone, MeOAc, AcOH, Ac 2 O.|
|Problematic||Me-THF, heptane, Me-cyclohexane, toluene, xylenes, chlorobenzene, acetonitrile, DMPU, DMSO.|
|Problematic or hazardous?||MTBE, THF, cyclohexane, DCM, formic acid, pyridine.|
|Hazardous||Diisopropyl ether, 1,4-dioxane, DME, pentane, hexane, DMF, DMAc, NMP, methoxy-ethanol, TEA.|
|Highly hazardous||Diethyl ether, benzene, chloroform, CCl 4 , DCE, nitromethane.|