The best solvent is "no solvent" :-)...! Well, this is not possible in many cases, but it´s good keeping the idea in mind! As to the point which ones are really green or not, the answer is not universal because a solvent may be green from its operational point of view (e.g. many ionic liquids), but not green form the point of view of its synthesis and/or disposal. In my opinion, the most important to be considered is the issue of solvent recovery and re-use. If one can assure quantitative solvent recovery (no solvent loss) and long-term re-use, than problems associated with being more or less greener become less important.
Sir, I think there is no real green solvent like water but may be ethanol is next green solvent since it is extracted from plants
you can check the GSK Solvent Selection Guide:
http://www.chem.utoronto.ca/green/_shared/pdfs/GSK%20Solvent%20Selction%20Guide.pdf
The best solvent is "no solvent" :-)...! Well, this is not possible in many cases, but it´s good keeping the idea in mind! As to the point which ones are really green or not, the answer is not universal because a solvent may be green from its operational point of view (e.g. many ionic liquids), but not green form the point of view of its synthesis and/or disposal. In my opinion, the most important to be considered is the issue of solvent recovery and re-use. If one can assure quantitative solvent recovery (no solvent loss) and long-term re-use, than problems associated with being more or less greener become less important.
2-Methyl-THF is highlighted the past years as kind of a green solvent because it can be made out of suger..
There is a very nice book which might be useful, maybe your library has it:?
Handbook of Green Chemistry - Green Solvents
Edited by Anastas, Paul T.
Published by Wiley
ISBN 978-3-527-31574-1 - Wiley-VCH, Weinheim
This depends very much on the context. Sometimes water is not a green solution - see http://onlinelibrary.wiley.com/doi/10.1002/anie.200604952/abstract ! If yields are reduced by changing the solvent then waste is increased.
The best approach is to identify the solvent characteristics that promote your reaction, or for other applications maximise productivity, then choose a suitably green solvent from those with the required properties. This may be water in some cases, but this is hard to predict without experiment because of hydrophobic interactions and similar phenomena (http://onlinelibrary.wiley.com/doi/10.1002/anie.200462883/abstract).
Lets say that if hydrocarbon solvents have the ideal properties for your application, then I would not claim water is a green solvent, and instead try a terpene for example. Guides such as that of GSK and other pharma institutions will help identify the greenest solvent of a particular class of solvent.
https://www.researchgate.net/publication/231181398_Expanding_GSK%27s_Solvent_Selection_Guide__Embedding_sustainability_into_solvent_selection_starting_at_Medicinal_Chemistry
Article Expanding GSK's Solvent Selection Guide – Embedding sustaina...
Thank you all.
Svetlozar, this topic about ILs has been discussed in another question and the conclusion was clear: ILs are not really green. Some of the reasons given there are synthetic, disposal and toxicity issues.
Robert, 2-Methyl THF has also flammability, synthetic and health issues.
Prabakara, perhaps ethanol is the best choice so far, although with some safety issues due to flammability...
Juan, thank you and sorry for my ignorance... Regrettably, I do not have enough time to accompany all research gate questions... If the part in my answer concerning ILs has been already discussed, so please ignore it...
James, I agree on the methodology you propose, but one should not blame water as being a non-green solvent just because the overall process or reactions considered are not green.
On the other hand, terpenes are a vast family of natural hydrocarbons, but many of them are flammable VOCs of considerable toxicity.
Besides water, I nearly realized from practice in the last three decades that the following are RELATIVELY SAFE "Greenish!" solvents to work with: ethanol & its mixtures with water, acetone & its mixtures with water,ethyl acetate, THF [ I judged that because I saw a technician - responsible for the GPC instrument- using it generously & inhaling it, of course, for 5 years without any harm inflicted on him], and acetic acid ( when it acts as a solvent). I know that green chemistry puts other conditions on green materials but I like to emphasize the safety aspect to humanbeings & environment .
Deep eutectic solvents are a new generation of solvents and catalysts (DES e.g. can dissolve polysacharides). It could be made with natural compounds. Valerolactone is also classified as a green solvent
Say supercritical CO2 is another green solvent. Quite versatile in extraction of lipids from biomass. And it is being used as alternative solvent for catalytic oxidation, hydrogenation carbonylation because of the stability of CO2 and its relative ability to solubilize O2, CO and H2.
Distilled water is quite toxic that's why "green" is not necessarily associated with "non toxic" with regard to solvents. I find the ACS Green Chemistry Initiative Pharmaceutical Roundtable Solvent Selection Guide quite useful. My personal list of green solvents contains:
Water
Water/surfactant mixture forming micelle-nanoreactors
Supercritical carbon dioxide (sc-CO2)
Ionic liquids
Polyethylene glycols (PEGs)
Dimethyl carbonate, Diethyl carbonate, Propylene carbonate
Glycerol (= glycerin)
Trimethylglycerol
Fatty acid esters
Ethyl (2S)-(-)-L-lactate and lactic acid
2-Methyltetrahydrofuran
(R)-(+)-D-limonene
Dear Juan,
Please contact your colleagues from IUCT, Alvarez de Castro,63, E-08100 Mollet del Valles and have a look at
Carles Estévez, sustainable Solutions - Green Solvents for Chemistry, In: R. Höfer, ed., Sustainable Solutions for Modern Economies, RSC Publ., Cambridge (2009) pp.407-424.
Best regards
Rainer Höfer
------------------------
Dr. Rainer Höfer
Editorial Ecosiris
Klever Str. 31
D- 40477 Düsseldorf
Tel.: +49 (0) 211 4920479
Fax: +49 (0) 211 4920477
Mobile: +49 (0) 172 2418861
E-Mail: [email protected]
www.ecosiris.eu
Thank you all.
Nizar, I agree on the "greenish" character of ethanol, ethyl acetate, acetic acid and even acetone (in spite of its high volatility and flammability), but THF could produce health problems at long term, performs quite badly in safety and is much too reactive...
Magdalena, Many DES have problems due to toxicity against human or environment and solid state of them at room temperature.
All, Please try to cite specific solvents instead of families of compounds, which have necesarily a variety of properties.
Raffaello, You can drink distilled water without any problems (in spite of myths based on the rupture of issolated cell membrane in pure water). Nobody would try to do the same with the rest of the solvents you list...with the exception of some esthers of fatty acids (edible oils).
This is a tricky one, but there are several solvent guides available - GSK have published theirs along with quite a bit of analysis/discussion, as have other pharma companies, with broad agreement. Look for the GSK solvent guide. However, as mentioned above it depends what you do with it, as this will limit the options available as well as influence what you do with it afterwards. Indeed there are people who would argue that water isnt green due to the issues of how you decontaminate it afterwards (you certainly wouldnt drink an aqueous waste stream, even though you would drink water!). It also has a much higher heat capacity than the average organic solvent and much higher latent heat capacity, meaning higher energy costs in heating / distilling. If these are relevant in your process then this might be an issue.
there are so many issues around solvents which have to be taken into account (some generic - toxicity, flammability etc, some specific to the process you want to carry out - solubility / reactivity etc) that it is hard to be exact without having a process in mind and evaluating the whole process. Obviously the generic properties would be the first line of choice and would eliminate many early on, but its the overall impact of the process (and recovery / disposal than will ultimately decide.
Although I have some reservations calling the dialkylated imidazolium salts "green solvents", they do offer alternatives to the "non-green" solvents for common organic reactions. Almost any organic reaction that we are familiar with can be run in these solvents and (in theory) in most cases the product can be extracted away from the solvent, allowing the solvent to be re-used in another reaction. In practice, the reaction mixture is poured into water and the product crashes out -- thus negating the "green" benefit.
If Dr. Zeinab means Poly(ethylene glycol) then I shall add polymers to the list: Poly(vinyl acetate) since it is used in chewing gums. Cellulose also is within this category as well as casein. Of course, the polymers are solids & are only fit to form solid solutions.In such case, the major component is considered as a solvent.
Obviously I wouldnt drink neither waste water, without previous purification, nor most of here listed as "Green" solvents even if they are pure!
Thank you, Zeinab.
Polyvinyl acetate is not liquid under standard conditions, is it?
PEG=Poly(ethylene glycol) is a viscous liquid at room temperature.
Dr. Juan, I agree with your comments. Maybe solvents mentioned above can only be a good alternative to solvent water.
The greenest solvent is the solvent that makes your process or product have the least environmental impact. If the solvent is to be used in a consumer product and emitted by the consumer into the environment, then water is probably a green choice. If the solvent is to be used in a manufacturing process then water is not likely to be a green solvent, because the clean-up of the solvent at the end of the process will cause a lot of environmental damage.
Ethylene glycol is a toxic liquid capable of produce poisoning.
We should not confuse green solvent and green process. A process or product can be not green even if it uses a green solvent such as water. Obviously the rest of components involved are also determinant of the overall environmental impact.
Ionic liquids have been discussed in a different thread with a clear result: they can not be considered as green solvents, even if they are greener than some of the classical organic solvents.
Ionic liquids are considered as green solvents because they are recovered and reused several times.
I would like to recommend the review paper by Jessop "Searching for green solvents", Green Chem., 2011, 13, 1391.
Rajendran, just to correct you please see the discussion on ILs and green solvents in ResearchGate.
Thank you, Fredrik. Quote from your reference:
"Zhang et al.23 compared acetone,
benzene,water and [bmim]BF4 in terms of environmental impact
by 11 factors, and included the impact of both the solvent
itself and its synthesis. They found that the ionic liquid was
the worst in every category except ozone-layer depletion."
Dimethyl carbonate is another option:
http://pubs.rsc.org/en/content/articlepdf/2012/gc/c2gc35337g
deep eutactic solvents.
see this paper
https://www.researchgate.net/publication/308164132_PHYTOCHEMICAL_AND_PHARMACOGNOSTIC_STUDY_OF_CATHARNTHUS_ROSEUS_USING_DEEP_EUTECTIC_SOLVENTS
Article Phytochemical and pharmacognostic study of Catharnthus roseu...
Ethylene glycol and its ethers derivatives are good green solvents other than water.
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