Properties: no harmful vapor, fully recyclable and non-flammable. Disadvantages: may react with lignin to form adsorbable organic halides (AOX)? Example: chlorine compounds (Cl2, ClO2) in bleaching of pulp. AOX generated during the chlorination stage. What is your opinion?
This question would require a long detailed answer. However suffice it to say that in my opinion ionic liquids are not necessarily or intrinsically green. However they represent one of the tools to be considered when designing a green process. An ionic liquid becomes green if its synthesis, use, application, recovery, and disposal all contribute to achieve a greener and safer process.
This question would require a long detailed answer. However suffice it to say that in my opinion ionic liquids are not necessarily or intrinsically green. However they represent one of the tools to be considered when designing a green process. An ionic liquid becomes green if its synthesis, use, application, recovery, and disposal all contribute to achieve a greener and safer process.
I believe, Alvise has answered your question lucidly. Most of the ILs I know do "act" as green compound once they are obtained in the pure form!
It depends on the efficiency of reusability, if you lost a small amount each time hence you must balance the impact into the whole process even if its lab scale.
Yes it can be considered green chemistry if it can be immobilized onto a solid support to become a heterogeneous catalyst. Many papers have now been published in this area.
yes it is, but depends on the ionic liquid too. The best way is to immobilized onto a solid support. Many papers concerning their immobilization as well as their toxicity have been already published.
Realistically, any solvent canot be green if you use an organic solvent to make it. That is reality. If one makes them without using solvents, and they consist of cationic and anionic components with which living systems are familiar with (i.e. non-toxic) you can make a case for them as CATALYSTS.
However, in very specialized cases when nothing else works as well, they may find useful applications as tools to study new chemistry.
IL Ionic liquids, usually based on 1,3-dialkyl imidazolium or pyridonium cations, which have weakly coordinated counter-ion, currently receive much attention, because of their thermal stability, a negligible vapour pressure, being inflammable and their catalytic effect on many types of reactions.
Although industry has already started to incorporate IL-based applications like the BASIL or the Dimerosol process, the wider use of ILs has to be evaluated as many reports pointed the hazardous toxicity and the very poor biodegradability of most ILs.
ILs with high purity are also required since impurities, even in trace amounts, affect their physical properties.
Additionally, their synthesis is far to be environmentally friendly since it generally requires a large amount of salts and solvents in order to completely exchange anions.
Ionic liquid in galvanic industry avoids the development of hydrogen and have no vapours. Let's say the ideal solvents for electroplating. Unfortunately they are still expensive for a wide use.
I have used IL for cellulose dissolution and reaction, and I´m not very pleased with it. If we do not strictly control the quality of cellulose and other reagents, a small part of the IL is lost or contamined with chromofores, that may reduce the yield of future reactions, when it is reused.
ILS can be considered as green if you used for replacement the hazard and volatile organic solvents and also for avoiding byproducts.
Ionic liquids are the solvents of 21st century.
Ionic liquids application in analytical chemistry, especially in separating analytes, is merited because ILs have some unique properties, such as negligible vapor pressure, good thermal stability, tunable viscosity and miscibility with water and organic solvents, as well as good extractability for various organic compounds and metal ions. In my opinion When they are applied instead of harmful and hazardous solvents such as CCl4 etc. they can be classified as green solvents.
Green index is a relative parameter.. The use of IL is a greener application compared conventional organic process as it has inherited green properties as mentioned above.
A lot has been said already which I am not going to repeat. In my opinion ILs can prove to be "greener" than conventional organic solvents for very specialized and fine tuned processes (like the industrial processes mentioned above) - but not necessarily "green" altogether.
For that they have to be able to be re-used for an extended period of time without the need for elaborate purification. This could even offset a potential environmental impact during the preparation of the IL. (Bio)degradability remains an issue but there is a whole subclass of imidazolium based ILs with ester sidechains which are supposedly easily biodegradable - just don't pair them with fluorine-heavy anions. Due to the very specific properties of every single IL I don't think though that they will be broadly used and don't appear to be a general substitute for organic solvents (yet?).
The potential to immobilize them on a solid support has been mentioned earlier. Another possibility is to use functionalized ILs as "liquid support" for reagents (e.g. Handy et al. J. Org. Chem. 2005, 70, 2874) or catalysts (e.g. Clavier et al. J. Organomet. Chem. 2005, 690, 3585) themselves or even as tags for a substrate from which it can be removed at the end of a multistep synthesis (e.g. de Kort et al. Tetrahedron Lett. 2004, 45, 2171).
ILs are not green considering the number of synthesis steps to make them. If they could be green then they would have to ve reused se eral hundreds times or more..!! Probably heptane is greener than most ILs....
Thanks for Your opinion and discussion.
Yes, it is true the many papers have been published in this theme. It is true that the green index is relative parameter and ILs is classified as green solvent, the solvent of 21st century. On the other side they have pointed the hazardous toxicity and their biodegrability is very poor. Synthesis of these compounds is far to be environmentally friendly.
My question is based on information generate the AOX during bleaching of pulp. “Chemistry of ClO2 bleaching is complex since due to the reduction there are several intermediates present during the process: chlorate, chloridedioxide, chlorite hypochlorous acid, chlorine, chloride.”
AOX are formed as a result of reaction between lignin, hexauronic acid from wood components and chlorine and its derivates use for bleaching.
Chlorine based bleaching process effluents produces dioxine, polychlorinated biphenyl and carbon tetrachloride and specially AOX.
These dioxins are quite resistant to degradation and have an elevated potential for bioaccumulation.
If AOX production had been true, or possible for ILs, then result is that ILs are not green solvent and terms of green chemistry is mistaken or even deceptive.
The use ILs to could feature an ecosystem risk.
I do not know of publications that discuss about the formation of AOX with ionic liquids
If one-step operation is considered , sure that It is green , however, whether it is green or not depends on the total procedure in synthesis and application of a ionic liquids. IF the total procedure is less engergy and clearer than the old one, ionic liquids is greener, otherwise, black
Ionic liquid hepl minimize use of chemicals by reducing the procedures and reuse of ionic liquid based reagents and solvents.
I have passed your question to Mr Russ Phifer who is an environmental consultant & his answer was as follows "the use of ionic liquids can certainly be considered green chemistry in some respects. When used as a solvent, an ionic liquid would not contribute to greenhouse gases. Also, as wastes, they are easier to dispose safely than many liquids. However, they are generally considered to be toxic to marine life, so if they are discharged with wastewater to the river, that would not be “green”. I hope this answers your question."
Russ
Russ Phifer
WC Environmental, LLC
So i hope this answer your question
good luck
hathama razooki hasan
I totally agree with the opinion of Hathama Hasan and Mr. Russ Phifer.
I think there is nothing essential that added to my recent answer (ILS can be considered as green if you used for replacement the hazard and volatile organic solvents and also for avoiding byproducts)
Michal, it is a very complex question. It depends what you want to use it for and what kind of IL. My experties goes to cellulose and there it seems that it is good substitution of convetional solutions. If the production of AOX is correct while using IL than you are right.
Neviem ci si ma pamatas, som absolvent z plastov a robil som s MIsom Jassom. Raz si mi aj posielal nejake materialy o celuloze. Teraz by som ti ja poslal mozno pre teba zaujime citanie. maj sa
Ionic liquids are toxic. Synthesis of nanoparticles or catalytic reactions carried out in ionic liquids are often called green because ionic liquid replaces large amount of surfactant, solvent and multi steps of the synthesis.
The 12 Principles of Green Chemistry13
It is better to prevent waste than to treat or clean up waste after it is formed.
Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.
Whenever praticable, synthetic methodologies should be designed to use and generate substances that possess little or no toxicity to human health and the environment.
Chemical products should be designed to preserve efficacy of function while reducing toxicity.
The use of auxiliary substances (e.g. solvents, separation agents, etc.) should be made unnecessary whenever possible and innocuous when used.
Energy requirements should be recognized for their environmental and economic impact and should be minimized. Synthetic methods should be conducted at ambient temperature and pressure.
A raw material feedstock should be renewable rather than depleting whenever technically and economically practical.
Unnecessary derivatization (blocking group, protection/deprotection, temporary modification of physical/chemical processes) should be avoided whenever possible.
Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.
Chemical products should be designed so that at the end of their function they do no persist in the environment and break down into innocuous degradation products.
Analytical methodologies need to be further developed to allow for real-time in-process monitoring and control prior to the formation of hazardous substances.
Substances and the form of a substance used in a chemical process should be chosen so as to minimize the potential for chemical accidents, including releases, explosions, and fires.
The 12 Principles of Green Chemistry
It is better to prevent waste than to treat or clean up waste after it is formed.
Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.
Whenever praticable, synthetic methodologies should be designed to use and generate substances that possess little or no toxicity to human health and the environment.
Chemical products should be designed to preserve efficacy of function while reducing toxicity.
The use of auxiliary substances (e.g. solvents, separation agents, etc.) should be made unnecessary whenever possible and innocuous when used.
Energy requirements should be recognized for their environmental and economic impact and should be minimized. Synthetic methods should be conducted at ambient temperature and pressure.
A raw material feedstock should be renewable rather than depleting whenever technically and economically practical.
Unnecessary derivatization (blocking group, protection/deprotection, temporary modification of physical/chemical processes) should be avoided whenever possible.
Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.
Chemical products should be designed so that at the end of their function they do no persist in the environment and break down into innocuous degradation products.
Analytical methodologies need to be further developed to allow for real-time in-process monitoring and control prior to the formation of hazardous substances.
Substances and the form of a substance used in a chemical process should be chosen so as to minimize the potential for chemical accidents, including releases, explosions, and fires.
People are often use the term ‘Green’ whether using ILs. However it is all about relative that how it correlates with the principles of Green chemistry
I think, before answer to your question , is to definited the word "green". If "green" is associated to ecology so, do you think that chemistry can be "green"" ?
Green Chemistry is defined as the ‘‘design of chemical
products and processes to reduce or eliminate the use and
generation of hazardous substances.’’ (P. T. Anastas and J. C. Warner, in Green Chemistry: Theory and Practice, Oxford University Press, New York, 1998; I. Horvath
and P. T. Anastas, Chem. Rev., 2007, 107, 2167.)
Dear Levillain, Kindly read the above post by Sebastien Djenontin, and you will get to know that chemistry can be green.
As ILs posses wide structural possibilities, you can not generalize all ILs as green. Their properties vary throughout the both extremes; from highly toxic to benign, from resistant to biodegradable, from non-flammable to combustible, etc.
But as stated above by Marco Noe quoting Seddon, they can be designed to be environmentally acceptable, e.g based on choline (essential nutrient) cation..
Regarding this issue it is interesting to read: “Searching for green solvents” Philip G. Jessop. Green Chem., 2011,13, 1391-1398. In any case, I think that ILs are far to be green ideal solvent by themselves. It is true that in principle ILs can be design to be green. On the other hand, the unique properties and performance of the ILs can lead to process that are greener than the conventional ones using traditional solvents. So they point is not if they are green rather if they can contribute to reduce the impact of our process.
Dear Michal and other participants of this discussion:
I've done a full PhD-research on this very topic, and my opinion is that ILs are indeed green solvents, if one carefully select them.
One of the best examples is application of a very CHEAP IL ZnO2.4H2O for Biomass valorisation. Ref.: http://www.google.com/patents/US20120178921
Warmest regards,
Igor
I think the comment of Alvise Perosa contained the essentials of this matter. I support his opinion - could not have commented better myself. RS
Use of ionic liquids is not a completely green process. Because there are some ionic liquids which are specially imidazolium based are toxic in nature because they liberate hazardous HF. But use of ionic liquids in the organic synthesis is preferable because of its reusability which prevent the waste to the environment and make the process environmentally benign.
I guess everybody before me has pretty much answered you, Michal. So, to sum up, "green" should be used for a process, not a particular compound, because "every substance can be considered poisonous, depending on the dose". Some of the ILs have already been shown to have a high water toxicity (especially the bistriflates), but as long as you prevent them from getting where they shouldn't be, they may be considered as "greener". E.g. in extractive distillation, where ILs are used for breaking azeotropes, you save up on the entrainer (which, if it is an IL, may be used in smaller quantities than e.g. the conventionaly used DMF) and you save up on operational costs, because you later don't have to distill the product from the entrainer. I hope this helped you in getting an idea.
Really the matter is that, "green" and "sustainable" are two over used words like "nano" and "bio" may be it is coming the time for a responsible use of terms.
Despite the advantages of ionic liquids still there are some limitations:
1. Expensive in comparison with classical organic solvents.
2. Very few commercially available.
3. Viscous
4. Poorly biodegradable and potentially toxic.
If green chemistry is correlated to the so called Environmentally friendly concept, I do not see ILs as a solvent for green chemistry. Some scientist trying to promote their research based on green chemistry concept but in reality it has no thing to do with green chemistry, or they might be correct if we could classify green chemistry into different topics. Green chemistry is a long process to achieve, but to start with the concept "green chemistry like" is a good start.
Of course there are limitations, the technology is only 15 years old and when compared to industrial processes known and constantly optimized for over 100 years I think it is quite normal that there will be problems here and there.
Don't get me wrong, ILs are not as green as many have hoped, or as green as advertised, but I have to agree completely with Magdalena- there are no green chemicals ( unless you classify DMF, NMP, MeOH, CCl4 etc as green, although unlike ILs they are cheap, commercially available and low viscous), there might be only green processes or even if not green completely, then at least greener than others.
Things like Ethylammonium nitrate (1st IL discovered almost 100 years ago) can be actually quite cheap and are biodegradable and not really toxic .
Just to complete this latest Boyan's post - the place to be now for ILs is precisely toxicology. Precious little data on their ecotoxicity and environmental fate, including biodegradability. But once we find patterns in structure that lead to their low or high toxicity and/or biodegradability, we'll be nearer to "green" applications.
There is nothing called green , Red , yellow chemistry .. there is only one chemistry that is chemical chemistry !!
chemistry itself will not and never bee green :)
Mr. Marakatti said it better than I -- chemistry is chemistry, it is the chemists and engineers who decide what reactions and components should be used. And don't ask about the toxicity of ILs -- so little known.
May be not in all circumstances, it all depends on the system and the liquid type.
"There are green chemistry measures [atom economy, atom efficiency, carbon efficiecny, environment factor etc.] on the basis of which we can assess the greenness of the method."
Yes Mr. Kumar, but still most of these criteria are just more qualitative criteria,,,
P.S. Do you know how to calculate "atom economy"?
About a quantitative evaluation of how green a process is LIFE CYCLE ASSESSMENT (LCA) can be mentioned.
Hi, Monica, it is true, that LCA analysis is very important. Because a life cycle assessment (LCA) is essential before any legitimate claims of used term "greenness". Application to processes, which are key parts of the life cycle, is important in the context of process design and development.
The case is when you are to use ionic solvent, in the end of the activity will there be any hazardous byproduct?. This I think may not be in all cases. In human and environmental unfriendly situations we have to avoid. More over, we may not really have 100% green solvents. That is why we have to research to improve on ourselves. More often we got to use some of these solvents even as green chemists because we do not have alternatives. Please find this material which might help.
The very question "Is the use of ionic liquids really green chemistry?" is rather undefined to have a single clear answer... yes, no, may be... Everything, depends on the specific case and, not only on the ionic liquid used as some would think, but everything around it. Even in what concerns the energy source used to produce it and than to perform the separation... The same process can be "green" in a given place and become not "green" in another one. The main difficulty of any LCA analysis stems from the fact that nothing could be claimed before it, and even reaching some conclusions (which at a first glance may appear reasonable), there is a high degree of uncertainty intrinsic to the LCA itself... Well, it is better than nothing, but still never rely to much on it...
Any process that reduces waste or re-uses solvent, is green. So it is not whether IL or any other substance is green. It is whether the process is more economical in terms of raw materials, energy and waste
I would agree with Larry´s comment if by "any process", he means the whole chain - extraction of the required raw materials - synthesis of the IL (or any other target compound) - use of this compound - end of life of this compound (re-use, recycle or disposal). Otherwise, it is useless to develop a process, which is "green" in the part of applying, say an IL (which is often the case of using an IL as clearly a better and less problematic solvent), but transfer the problem to the stage of its synthesis, which could be far from being "green" or its disposal ("end-of-life" stage, if this IL is toxic).
It is true, and recycling and/or regeneration have to be very efficient (>99%), by reason of price, and it is problem application in industry
It is most probably one of the promoted "fake" Green chemistry alternatives. Price, carbón trace and how you get rid of it are factors to be taken into account in order to entitle a process as ecological.
Yes halogenated ionic liquids are not more green now..................... U can find halogen free ionic liquids............... N try to avoid aromaticity also.............then they will be green.......... Otherwise the ionic liquids are green in many ways................
The ionic crystals if are used in photovoltaics can be green chemistry or physics. However,if also their preparation is green chemistry then we can speak of green, but again nothing is absolutely green! Everything is relative as Einstein told us.
Theo I disagree with your phrase of that "nothing is absolutely green!", Because, the pure water (H2O) is absolutely green as an example.
green chemistry doesn't mean to be pure green Rabah Khalil........... its mean is a step towards green
I know Rashi Gusain if you use water, acetic acid and alcohol for preparing ester as an example, the product is quite green because it will be used for food industry.
Agree wid u bt u r thinking for only one way................ For many other applications which are not green u cn make them green by the use of halogen free ionic liquids if u can use there it........... I were saying only that
Catalysis is one of the principle among the twelve principle of "Green chemistry" In my opinion using ionic liquids as catalysts has contributed significantly in the field of, catalysis chemistry = Green chemistry. " The best thing about the IL that I personally like is there role in reaction mechanism " spatially how both cation and anion help each other in catalyzing reaction i.e "Ambiphilic catalysis"
It is true the term green is controversial. Wood is pure green product and relieves volatively organic compounds (VOCs). Concentration of VOCs in these different environments can be considered pollution.
Ionic liquid dissolve lignocellulose, only solvent, not react with lignin or cellulose
I essentially agree with Dr. Perosa. Furthermore, in my view, only chemistry based on biodegradable compounds should be considered as fully green. Unfortunately, history tells us a number of cases where commercial compounds initially considered as safe, stable and innocuous, have been finally proved to be harmful for the environment. Well known examples are CFCs or DDT. In this way, we should be especially cautious with halogenated ILs.
Yes Mr. Juan Casado, the more problem is with halogenated ils........... but if we try to prepare some ils which are free from it then we can move a step towards green ..........
The major problem with many ionic liquids is not their toxicity but the very difficult synthesis. The synthesis from natural resources (i.e. minerals, crude oil) takes 20-35 synthetic steps, depending on the ionic liquid, compared to common organic solvents which take only 0 (e.g. hexane) to 8 steps (e..g DMF). The environmental impact of those 20-35 steps is likely to be greater than the environmental impact of the solvent itself. This problem would be solved if the IL could be 100% recycled over and over, but that's not the case. Recycling of solvents is never 100% and the recycling process itself causes environmental impact.
In answer to the comment about water being a perfectly green solvent, it's not. Once water has been used, it is contaminated. The subsequent clean-up of the water can sometimes be quite environmentally damaging. Therefore water may not be as green, for some applications, as organic solvents.
But in some cases ionic liquid does not react to form such obnoxious substance. More so in one of the 12-principle of green Chemistry, is to develop equipment capable of detecting and removing any harmful materials. Having seen a liquid that got these wonderful properties as a green reagents, is high time we started using facilities that can detect and remove any obnoxious materials from such systems.
Ionic liquids usage is Green Chemistry
In some cases not, but in some cases they do react to form pollutants, either in their production or in their usage. Perhaps ILs are greener solvents than usual organic solvents, but they are not really green solvents.
It hard to generalize like that. This big problem with halogenated ILs for example, Choline chloride is a chalogenated IL, and seems to be quite safe. I would have a much bigger problem with choline FAP for example, because of its toxicity and persistence.
The problem of ionic liquids is not their toxicity but the very difficult synthesis and their cost. I believe it is not save to environment?
Dear Sir
I proposed you read following articles:
DOI:10.1002/clen.200600015
DOI:10.1039/B419172B
subject of above articles is about of toxicity of ionic liquids.
At present R&D investigations have been pusued to explore the application of ionic liquids in several areas of nuclear fuel cycle because of some of their specific properties such as liquid at room temperature, molten at temperature < 373 K, negligible vapour pressure, better solvent for dissolution of a variety of organic and inoganic compounds, high thermal conductivity. But we cannot classify them under green chemistry category. The synthesis of Ionic liquids involved several steps which need a lot of attentions. Those chemical steps pollute the atmosphere. Hence how can we tell IL as environmental friendly.
May I please ask what is so ungreen or toxic about let's say Ethylammonium nitrate, the first ionic liquid or things lick Choline lactate? The world of ionic liquids stretches far beyond BMIM BF6.....
Ionic liques based on Pyridin can not be called green, but there are other solutions. And true Etyhylammonium nitrate is much better, but also such as Eutetic solvents
http://onlinelibrary.wiley.com/doi/10.1002/ejlt.201390012/full
I think I've read that ionic liquids are consider as emergent contaminants. Is it right?
As someone with a a chemical engineering background I can also add that one problem with ILs is their poor transport properties compared to water, e.g. viscosity. This means, for example, that more energy is required to pump the same amount of liquid. So they may possibly require greater use of energy to achieve the same goal. For transition metals processing they can also have a surprisingly limited capability to dissolve metal salts compared to water, so you need more solvent. I'm not sure if it is one of the 12 principles, but less solvent is always better from a safety, cost and process intensification perspective.
As Alvise pointed out, greenness totally depends on the alternatives available. In some applications ILs are the least bad option, in others they are clearly inferior to ordinary solvents.
I say least bad option because I think the idea of 'green chemistry' is marketing nonsense. Chemistry can be a lot less harmful to the environment, but the moment you get almost any chemical in a highly pure form, in large enough quantities, it becomes a potential environmental disaster. Just try throwing a big pile of NaCl or sugar in a small enough lake and you'll see that even the most common, natural substances are not as harmless.
Personally, I agree with Boyan that ILs based on non-fluorinated complex anions are quite interesting, particularly those derived from readily decomposable cations, such as choline.
Please don't get me wrong, this doesn't mean that all ILs are edible, or that some are not persistent or toxic, but generalizing gets us nowhere. For all people, who are afraid of the toxicity of ILs, I would recommend to take a peek at the R ans S labels for everyday things like Aspirine (T) or Cetylpyridinium chloride (T+), which is used in almost every mouth wash or cough drops.
Swallow 500g of salt at once and see what happens. The amount is what makes a compound toxic, just as David mentioned.
Some ILs are gree but not all. It depend on the application, recyclibility, toxicity an other parameters
I give u some of the articles related to ur search....
Pure Appl. Chem., Vol. 72, No. 7, pp. 1391–1398, 2000., Research Journal of Chemical Sciences, Vol. 2(8), 80-85, August (2012)., Chemical Engineering
57/1–2 (2013) 53–54., doi: 10.3311/PPch.2170., Mini-Reviews in Organic Chemistry, 2012, 9, 000-000., subject of above articles is about toxicityan applications of ionic liquids.
Dear Sir
I proposed you read following articles:
10.1080/17518253.2011.572294
10.1080/17518253.2011.572295
Ionic liquids satisfy certain conditions of Green solvents. For example, the high boiling points prevent emanating of vapors. Further due to high boiling point and often miscibility with water make recovery of ionic liquids easy. Basing on these two factors, ionic liquids can be grouped under Green solvents.
I fully agree with Alvise!
Let me add that there is in general no "intrinsically" green method, process, or product. The often advertised use of water as the "ultimate green" solvent, for example, also has some potential drawbacks and limitations (e.g. high energy requirement for removal, aqeous waste streams with low concentration of organics). Or take renewables: Biobased materials may consume more energy or be of higher toxicity than petrochemical products. etc. etc.
The 12 principles of Green Chemistry do not provide answers, they define a systematic framework from which researchers can define scientific and technical challenges to generate fundamental knowledge and innovative know-how aiming at more sustainable chemical processes.
If one considers ILs simply as drop-in replacement to be used in a fully analogous manner and with the same quantity as conventional organic solvents, they are unlikely to provide a "Greener" solution. However, a large number of examples and applications show that their properties allow the design of novel molecular control mechanisms, innovative reaction engineering concepts, and technological solutions (quite a few in fact outside synthetic chemistry). For some of them significant and measureable improvements towards the goals of sustainability have been clearly demonstrated:
Thus, Green Chemistry provides a motivation to do research on ILs, but not all research on ILs is by default Green Chemistry.
Recently, Chris Hardacre had a talk on ILs at our Institute and his conclusion is "not always" :-) http://www.icpf.cas.cz/en/recordings-e-h-la-lectures.
From their synthesis ILs are not green but their characteristic properties, makes them more environmentally friendly and therefore considered benign. Recyclability does not impact "green" , rather it creates the ability for a material to be contained within a designed environment without its loss to areas where its toxicity is felt.
Dear Mr. Green, as long as you have used one barrel of IL, which has not evaporated in the atmosphere instead of 3 barrels of let's say methanol, say 10% of which have evaporated during your process, you are quite greener with the IL than you are with the methanol. And you treat the IL exactly the same way you would treat your normal solvent, i.e. you recycle it.
Andy Abbot had a very nice talk a few weeks back at the COST EXIL meeting in Dresden. From the let's say 300 organic solvents that are used in synthesis, only about 10 or so are used on a really large industrial scale. It is utopic to think, that ILs might replace those.
I agree with Boyan lliev and others too, speaking for IL's are the green solvents. Really, they well discussed from their point of view. Of course, the IL's are in agreement with the principles of green chemistry, but it doesn't obey the cost effective, one of the highlight principle of green chemistry . Joaquín García-Álvarez well discussed the requirements for its synthesis. And their recovery and disposal are not easy in a greener manner as telling, For eg. water the green solvent, cheaper, no hazardous, easily separated, disposal doesn't matter. When we are sure with water- the green solvent , how can we agree IL's under green solvents??????
If you go by the color of the ionic liquids, then they are not green. If one go by the composition or the constituents of the ionic liquids then except carbohydrate or amino acid based ionic liquids, all are synthesized from potentially hazardous chemicals. But after formation of the ionic liquids , their minute vapour pressure, recyclability, biodegradability helps the researchers to use them as green solvents.
Not all Ionic Liquids are Green,yet you have many types of green ionic liquids.This is depending on your choice ,your requirements and tasks.The careful selection of ionic liquid compositions certainly will in many cases leads to Green Ionic Liquids.
The statements are a quotation for specific purpose and is hardly to be considered as general question.
A better answer to your concern is to specify your task if any, and you will receive a more precise explanation.
Ionic liquids are green solvent due to its some property as low vapor pressure, thermal stability, non flammable. But in some way its have drawback as disposal problem, high viscosity (separation of product or catalyst). In this way, it is not following the principal of green chemistry. That's why it'll not consider as a green solvent.
Taking all these comments together I think the conclusion must be that there are no such things as green solvents. Only a particular process can be green. The choice of solvent can make a process relatively greener, but even that is a complicated analysis full of subjective factors and likely to depend on scale. Given that Ken Seddon estimates that we can devise millions of ionic liquids, which will all have different properties, it is meaningless to try to find a simple answer to this question I think.
An ionic liquid is not green but it becomes so if its synthesized in a safe manner.
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