Greener solvents

The shift toward greener solvents can also be observed based on the solvent waste breakdown. Table 3.1 displays the EPA s TRI data from 1995 and 2006. Included in Table 3.1 are the top 20 chemical wastes generated in 1995 and 2006 and the corresponding ranks for both years from the pharmaceutical industry. There is a noticeable decrease in the use of hazardous solvents such as methanol and toluene. It is interesting to note that in both 1995 and 2006, the top 20 released chemicals accounted for more than 90% of the overall TRI releases. 

This could be due to several factors such as process operability and Environmental Health and Safety (EHS) concerns as GSK shifts toward greener solvents. It was noted that between 2000 and 2005 the average per stage mass usage of dichloromethane per kilogram of intermediate produced had only decreased from 16.4 to 15.3 kg/ kg intermediate. It has been reported that as dichloromethane currently accounts... 

The Roundtable has undertaken two rounds of benchmarking the routes of manufacture used by its members to prepare APIs. This exercise shows areas where improvements can be made and provides metrics for tracking improvement in the future. In 2009 a Roundtable sub-group started a project to influence solvent manufacturers to produce greener solvents. 

Hot water is attracting attention as an extraction solvent in the recovery of compounds from plant material as the search for milder and greener" solvents intensifies. The use of hot water as an extraction solvent for milk thistle at temperatures above 100°C was explored. The maximum extraction yield of each of the silymarin compounds and taxifolin did not increase with temperature, most likely because significant compound degradation occurred. However, the time required for the yields of the compounds to reach their maxima was reduced from 200 to 55 min when the extraction temperature was increased from 100 to 140°C. Severe degradation of unprotected (plant matrix not present) silymarin compounds was observed and first-order degradation kinetics were obtained at 140°C. 

One important aspect that should be considered in future industrial processes to produce polyphenylene ethers is the use of greener solvents. In that context, some studies have been carried out to try to generate PPO in water [46]. Thus, Nishide and coworkers have developed a procedure where an aqueous solution of copper(II) complex (10mol%), that is, CUCI2/DTPA (DTPA = diethylenetriamine-A/ ,A/ ,A/ , A/ ",A/ "-pentaacetic acid), is mixed with an aqueous solution of DMP/NaOH 1/1, containing sodium w-dodecyl sulfate. 

The next step in selecting greener solvents is to critically evaluate the present solvent use. Many methods for solvent pollution prevention have been developed. 

In the short term, the possibility exists in some situations to exchange a greener solvent for a more hazardous one (direct swap ). Success in finding green solvents as drop-in replacements in existing processes is extremely variable. Inevitably, some adjustments need to be made, and some alternations in the chemistry are necessary. Listed below in Table XI are some examples of possible solvent alternatives. In this area a chemist s knowledge of solvents and chemistry are invaluable in utilizing alternative solvents. 

Black, H. (1996) Supercritical carbon dioxide the greener solvent. Environ. Sci. TechnoL, 30 124A-7A. 

Unique reactivity and selectivity of guanidine catalysts in some reactions renders them important tools of organic chemists. In order to make this powerful tool more relevant to green chemistry, improvement on existing synthesis routes with a focus on greener solvents and less waste generation, and development of useful enantioselective reactions with sustainable catalysis in mind are two possible areas for future development. 

Which of the following features of a solvent make it a greener solvent ... 

Zbinden MDA, Sturm BSM, Nord RD, Carey WJ, Moore D, Shinogle H, et al. Pulsed electric field (PEF) as an intensification pretreatment for greener solvent lipid extraction from microalgae. Biotechnol Bioeng 2013 110 1065. 

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