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Author: Subject: Alternative Solvents and New Solvents - General Discussion
BromicAcid
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[*] posted on 7-1-2008 at 16:59
Alternative Solvents and New Solvents - General Discussion


The focus of this thread has been retconned :P but that won’t make a difference if you are newcomer so read on.

This thread is to focus on solvents that we hardly hear about. Sure, we are all familiar with pyridine, benzene, dichloromethane, toluene, ethanol, etc. But what about benzotrifluoride? You could look it up and see the structure, but where to go from there? It’s a chemical that is being used most recently as a solvent, specifically as a replacement for dichloromethane in reactions. The point is that it is not one of our ‘traditional’ solvents. It’s a relative newcomer to the field, the first major paper on it’s use being published J. Org. Chem in 1997.

What I am hoping this topic does is expose some of us to what new solvents are being used in academia and in industry. What solvents are being used and pushed as replacements for our traditional solvents, and what are some of their properties? This is not meant to be something comprehensive, more of an open invitation to get some dialogue going between our members.

This sort of information is important in allowing us to transfer from newer work being done with these new solvents to our traditional solvents we use and also to do the opposite. The interesting thing being that although in the areas of organometallic catalysis and ligand chemistry the molecules are becoming increasingly complex and difficult to prepare, in many of these solvents they are already existing molecules only recently thought of as solvents and some of them have relatively simple structures, the types of things an aptly equipped at home chemist might be able to tackle.

So, feel free to name off some solvents being pushed as replacements for solvents of old. Solvents that are ‘new’ all together and just interesting news on the solvent front (if you’ll pardon the pun).

I’ll kick things off:

  • Cyclopentyl Methyl Ether C<sub>5</sub>H<sub>11</sub>OCH<sub>3</sub>

I was reading about this today in the newest issue of Aldrichimica Acta (Vol 40, No 4). Supposedly it can be used as a replacement for many of the ethers, MTBE, THF, Dioxane and others. It is resistant for forming peroxides, is stable to acids and bases, it does form an azeotrope with water, works well for organometallic reactions. The ACS has an article on this compound however it is for members only and the link only brings you to an outline with slightly more information. It can be prepared from reacting cyclopropanol with a methylating agent or by reacting cyclopropene with methanol under pressure.

  • 2-Methyltetrahydrofuran C<sub>4</sub>H<sub>7</sub>OCH<sub>3</sub>

What really makes this one earn its name as a green solvent is that it is renewable, it is made from corn cobs and farm refuse. Additionally it has a higher boiling point (allowing for stronger reflux) and lower melting point so it can be used at lower temps than THF. This compound as well as the one above are covered in a bulletin that Aldrich released concerning green solvents, a copy can be found on their site here.

  • Dimethyl and Diethyl Carbonate

The two of these compounds are fairly similar. The organic carbonates have a reasonably low toxicity compared to some of the other common solvents. Additionally Dimethyl carbonate has been receiving quite a bit of interest as an alternative to dimethyl sulfate, and methyl iodide as a methylating agent.

  • Benzotrifluoride C<sub>6</sub>H<sub>5</sub>CF<sub>3</sub>

Information on the developing solvent characteristics of this compound was obtained from:

J. Org. Chem.; (Communication); 1997; 62(3)

Basically the authors determined that it behaved similarly to dichloromethane and took it upon themselves to run a number of reactions in the solvent that were traditionally run in DCM with either easier reaction or equivalent reaction. The solvent has a higher boiling point which lends to higher refluxes and additionally there were some other notes on toxicity.


[Edited on 1/8/2008 by BromicAcid]




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UnintentionalChaos
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[*] posted on 7-1-2008 at 18:24


Catalytic Hydrogenation of http://en.wikipedia.org/wiki/Furfural yields 2-methyltetrahydrofuran....that also looks like it has the potential to be used as a "green" plastic

D-limonene is also available from citrus peel oil on a massive scale and finds it's way into many cleaning products...It can also be converted into poly-limonenecarbonate, which has similar properties to polystyrene




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microcosmicus
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[*] posted on 7-1-2008 at 20:21


I don't know if it would count as green, but what about DMSO?
Certainly, it's proponents make a big to-do about it being
natural. At any rate, it arises as a byproduct of the process
of making paper --- not the greenest activity, but at least
one does not have to make extra damage to the environment
to synthesize it.

By the way, since you raised this post, Bromic Acid, I would
like to than you for posting the stuff about electrolysis in
DMSO on your homepage. Inspired by your efforts, I ordered
a bottle of the stuff which just arrived. As time permits, I
plan to fiddle around with seeing what I can and can't
deposit in that medium.

As for the issue of good or bad for the environment, I suppose
"the dose makes the poison" applies here as well.
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chemrox
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[*] posted on 7-1-2008 at 23:26


http://www.chemsoc.org/ExemplarChem/entries/2004/bristol_vic...

http://www.rsc.org/ej/gc/2005/b418069k.pdf

are a couple of good places to read about them




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[*] posted on 7-1-2008 at 23:40


I understood that DMSO indeed is not very toxic, and some people use it to treat skin rashes. It is said, however, that DMSO is a great transport mechanism for other toxic compounds. E.g. aqueous solutions of metal salts only penetrate the skin and can enter the body very slowly, while DMSO solutions of the same salts quickly pass through the skin and the salt easily reaches lower-lying parts of the body.

To my opinion, every solvent, which is a byproduct of another commonly used and important process, may be considered green. You get the solvent at no additional environmental cost.

I do not think that non-toxic solvents must be called 'green'. If making a non-toxic chemical requires a lot of energy and natural resources, then its use may seem 'green', but the total environmental impact still is high.

In this entire discussion we must clearly distinguish between two kinds of 'green':
1) Green from the point of view of total environmental impact from production to waste
2) Green from the point of view of the person, who uses the material.




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JohnWW
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[*] posted on 8-1-2008 at 00:34


Quote:
Originally posted by chemrox
http://www.rsc.org/ej/gc/2005/b418069k.pdf

Someone with a subscription to the RSC's Journals, please download this item, and post it here. I could not download it - access denied.
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[*] posted on 8-1-2008 at 03:29
there you go :)


i re-posted it in: References » Wanted References and Needed Translations (3)

[Edited on 8-1-2008 by stoichiometric_steve]
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[*] posted on 8-1-2008 at 03:44


Quote:
Originally posted by woelen
.........

Exactly.
Whatever you would say - H2O is the "greenest" solvent.
This thread is about everything and about nothing. Lists, synthesis, properities ... ? Encyclopedias, articles, books.....




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[*] posted on 8-1-2008 at 04:15


2-methylTHF is also known as sylvan and is nothing new. I would expect the peroxide forming properties of this compound to be similar to those of THF, e.g., worse than those of Et2O.

MTBE has only earned a place in the Hall of Shame because the EPA and DOE upgefucked and approved it for use as a gasoline additive. It was never an environmental problem previously, mostly because it had few uses.

Dioxan (1,4-dioxan) IS a problem because it is a carcinogen.

When Aldrich is "pushing" products like this, look to the bottom line. "Green" solvents at what premium? Don't be a sucker for a current fad like this. The only reason to pay a premium for a solvent is if that solvent has real advantages that justify the expense. Otherwise let the chemical industry make and sell these supposedly environmentally benign solvents CHEAPER than the usual solvents, and promote their use that way, then I might believe them.

Too often in the history of industrial chemistry the rationale for many many products is that it is a waste product from other processes. The industry wants to turn its garbage into $$$ amd we get saddled with the downstream products, many of which in the fullness of time have turned out to be harmful. Best to avoid playing that game at all.




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[*] posted on 8-1-2008 at 05:26


Butyl acetate is said to be less harmfull than most solvents. Ethanol is probably as harmelss as solvent can ever be (excluding water of course). Diethyl ether can not be very harmfull as it has even been used for human consumption. Saturated hydrocarbons are rather harmless. Propylene carbonate is said to be of very low toxicity and seems to have some interesting uses too.

There are quite few of rather harmless solvents among most common. It would be interesteng to know why exactly are some exotic solvents called as "green" and how well these claims are founded. I would like very much to do my experiments with harmless and "green" chemicals but like Sauron, i am sceptical.


[Edited on 8-1-2008 by chromium]




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[*] posted on 8-1-2008 at 07:19


There's no h in butyl acetate.



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microcosmicus
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[*] posted on 8-1-2008 at 09:17


Quote:

Diethyl ether can not be very harmful as it has even been used for human consumption.


The only such use of which I am aware was as an anaesthetic in the
nineteenth centrury. However, I would hardly take the practice of those
times as a guide, otherwise I would be tasting chromium salts and
engaging in similarly questionable practises. The following website

http://www.anaesthetized.com/images/ether.html

lists the following effects

Unwanted effects of exposure to ether can include a cough, sore throat, painful red eyes, a headache, drowsiness, laboured breathing and nausea. Vomiting is quite common.

so, while it may not be downright toxic like H2S of HCN, I don't care
to be ingesting it either. I suspect it is not much different from other
common organic solvents in this respect.

Again, I think it is important to think quantitatively and put things in
perspective --- just how much chemical is being used in the lab as
opposed to other places? Personally, I am not too worried about
the the potential for environmental damage from metal salts and
solvents in my experiments especially since I do them on a micro-scale
(hence the pen name). Rather, I focus my efforts on being green on
things like what solvents I use to clean floors and windows or what
agents I use to unclog drains .

I assume it is similar on a larger scale in industry. While I can see the
impact of a company using a greener solvent in the large-scale
production of plastic or drugs, I doubt that going green in the lab
is going to anywhere nearly as significant an effect.

[Edited on 8-1-2008 by microcosmicus]
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not_important
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[*] posted on 8-1-2008 at 09:25


Quote:
...Diethyl ether can not be very harmfull as it has even been used for human consumption.


That's a bit faulty logic. Consider chloroform, onced in used in toothpaste
http://www.oehha.ca.gov/air/chronic_rels/pdf/67663.pdf

Older examples of toxic materials used in foods include the Victorian era colouring of candy and fancy baked goods using arsenic based pigments.
Quote:
Saturated hydrocarbons are rather harmless. ...


Not quite true, for example hexane:

http://www.jns.dergisi.org/text.php3?id=174

http://www.atsdr.cdc.gov/toxprofiles/tp113-c2.pdf

this is chronic exposure, at levels approaching and exceeding a part per thousand; hopefully one is careful enough to avoid such levels of exposure for extended periods in the lab. This may be an example of varying sensitivities in the population, from genetic differences in metabolism of alkanes and metabolic products. There's also evidence that acetone and other simple ketones may increase the toxic effects, but then acetone is common in the lab.
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[*] posted on 8-1-2008 at 10:45


My logic is very simple - if there are lot of people who were exposed to that chemical much more than i am - and it still did not ruin their life then there is no good reason to think that it ruins my life.

Logic of modern toxicity studies does not seem that reliable for assessing actual risks. There is usually no way to tell if those 1% or 3% or 10% who got serious health problems were not simply more sensitive than most of us are or they even might be those who have just bad hygiene or who got these problems with help of some other substances, diseases, heredity etc.

That said, when doing my chemistry i am always very carefull. I do most of work in microscale and fumes are always vented out but i think that quite remarkable part of modern toxicity and cancerogenicty fears are just result of misuse of statistics or of confusing general health and hapiness with lack of symptoms.This is just my point of view no need to agree with it.

Returning to human consumption of diethyl ether - in former soviet union it was sometimes used instead of vodka in small quantities. There is lot of folk tales about drinking ether and eating some hot food afterwards. I am sure this was more harmfull than drinking vodka or moonshine but it was not by far as destructive as regular use of inhalants or hard drugs.

[Edited on 8-1-2008 by chromium]




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microcosmicus
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[*] posted on 8-1-2008 at 11:11


Now that you mention it, I also do remember coming across stories of
people using vodka during the prohibition of the roaring twenties.
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[*] posted on 8-1-2008 at 12:06


Quote:
Originally posted by kmno4
Quote:
Originally posted by woelen
.........

Exactly.
Whatever you would say - H2O is the "greenest" solvent.


Cyclodextrins can be used as very nice "green" phase transfer catalysts. They can enable a fairly wide variety of chemistry to occur in aqueous matrices.

For example, a benzene ring will fit into the hydrophobic cavity of b-CD and Nap will fit into y-CD.

Cheers,

O3




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[*] posted on 8-1-2008 at 15:57


Yes, from what I've read, people used to drink ether based drinks during prohibition and even before and after.

Honestly, I just don't consider hexane very toxic. I mean, no more so than gasoline which consists of a significant amount of hexane.

I mean, yeah, you should take the average precautions that you would with any hydrocarbon solvent. To me, it's just a common sense issue. Just keep your exposure as low as you can. Sounds simple enough to me. Now carcinogens, mutagens, teratogens etc... are different, of course.




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[*] posted on 8-1-2008 at 16:25


"Green" materials and processes are particularly advantageous to amateur chemists, in my opinion, for a number of reasons. Green processes usually employ reaction conditions which are easier to reach without specialized apparatus. They're also tailored to waste minimization, which also translates to removal of unneeded reagents and sometimes easier workup too (see examples from J. Chem. Ed.).

Low-toxicity solvents and reagents may be more expensive, but they can reduce shipping hazards, thus shipping price. When it comes to use also, low-toxicity is good, because many amateurs work without truly professional fume hoods or waste disposal services. Less hazardous chemicals are also less likely to be withheld from sale to the public by suppliers.




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[*] posted on 8-1-2008 at 17:15


I was told once that hexane is significantly more toxic than pentane, and for this reason I bought pentane at the time instead of hexane. The problem here with that, is that ambient (outside) temperatures often enough exceed the BP of pentane (36.1 C), so the volatility is a problem.
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BromicAcid
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[*] posted on 8-1-2008 at 17:23


Originally this topic covered Green Solvents. But what I was really getting at was solvents that are being proposed as alternatives to traditional solvents. The usual trend though for this is that these alternative solvents are comparable or better in terms of their characteristics, and are usually safer, Greener. Hence my initial mindset on Green solvents.

Additionally this was not meant to be an all-inclusive topic (as in everything will be covered in great detail) but instead an open invitation to contribute whatever anyone felt so long as it was useful or relevant.

I wanted to see examples of solvents that are being explored and pushed that maybe we haven’t all seen before. I mean, when was the last time you flipped through your issue of CE news and saw an add depicting an old man in a rocking chair with the caption, “Do you remember when a solvent was a solvent? At Carbon Tet we remember, and we still make our carbon tetrachloride the old fashioned way, by photochlorination of methane, using all natural pure as rain sunlight. That’s right, our brand of carbon tetrachloride is all natural, the way nature intended, so when you’re looking for a solvent, a Cadillac of solvents, think Carbon Tet, your children will thank you.” Actually that was somewhat pointless, sorry, but I can’t bring myself to delete it.

Regardless, what are some of these new solvents? What are they used for and what are they replacing and what are their properties. And if things are simple enough how can we go about making them? Surprisingly most of these solvents seem to be fairly simple compounds especially compared to what you might see in a cutting-edge ligand or organometallic catalyst.

Additionally this kind of topic can be used in reverse, suppose you see an article in the newest issue of and organic chemistry journal that relies on Benzotrifluoride and you go, “What the hell?” this thread would hopefully then have the post that says Benzotrifluoride is being used in place of dichloromethane due to its higher boiling point which allows for a stronger reflux.

Anyway, the focus was not to be just Green solvents though there is a lot of research being done in the area, but also solvents that are being toted as alternatives to traditional solvents. Relative newcomers into the field that really haven’t had their limits tested in academia and just interesting solvents in general. Again, it’s broad but there is more to work with here, more freedom and we can leave the stigma of wondering what’s worse for us or what’s worse for the planet and just focus on the chemistry at hand people.




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chemrox
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[*] posted on 8-1-2008 at 21:01


Quote:
Originally posted by BromicAcid
The focus of this thread has been retconned


Translation please!




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[*] posted on 8-1-2008 at 21:14
saturated HC's tox assertions-> PTC quests


Quote:
Originally posted by not_important
[this is chronic exposure, at levels approaching and exceeding a part per thousand;


@Not_important .. there are few things that aren't toxic with chronic exposure above trivial levels .. I miss the old phisohex product .. anyway, today when confronted with a new agent I look for information dating from about 1950 and the decade after .. my childhood chemistry set had an experminet including an H2S generator but one of you is sure to say this explains some things...

But to return to the topic, I like acetonitrile whenever it can be used.. lots of solubility ..washes away readily (where is away, anyway?) and has been mentioned, ionic liquids where applicable. I have a PTC question for another thread. What makes an appropriate PTC? Why choose a tetraalkylhaloammonium salt over a PEG for example?

Cheers,
CRX

[Edited on 8-1-2008 by chemrox]




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[*] posted on 8-1-2008 at 21:15


Retcon From Wiki-

Quote:
Retroactive continuity or retcon is the deliberate changing of previously established facts in a work of serial fiction. The change itself is referred to as a "retcon", and the act of writing and publishing a retcon is called "retconning".


http://en.wikipedia.org/wiki/Retcon




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[*] posted on 8-1-2008 at 23:36


Quote:
Originally posted by Sauron
The only reason to pay a premium for a solvent is if that solvent has real advantages
that justify the expense.


@ BromicAcid
For amateur chemistry anything not OTC is just wishful. Specialty solvents only have
real world application in industrial scale process chemistry, and are in such instances
specifically engineered for that application and purpose. Sure, flourocarbons have
useful properties, but at a dollar a gram are beyond the budget of a hobbyist, or one
may try to synthesize these by the halex reaction. Chemistry performed in a reaction
vessel using non obvious solvation such as liquid CO2 would be more cost effective.
In practice the only reason to resort to a solvent is for the exclusion of water and
obviating hydrolysis, or for rendering polymers and resinous materials. A single solvent
on it's own has limited and specific utility, the blending of solvents to achieve desired
properties is a science in itself and in practice very much an art.
_______________

Increasingly rare because it's an ozone depleting chlorocarbon - trichloroethane is, was
very user friendly and nontoxic even less so than dichloromethane. Get it before it's gone !
http://www.retcoalloy.com/?page=shop/browse&category_id=...
.

[Edited on 9-1-2008 by franklyn]
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[*] posted on 9-1-2008 at 02:05


Ethyl ether (Et2O) was a popular tipple among medical students in the 19th and well into the 20th centuries and may still be in some places.

Usually referred to as going on an ether jag.

Probably not done in concert with cigarette smoking, at least not more than once.

This existed or exists in parallel to the diversion of high proof ethanol by students for making Purple Passion punch, etc.

That can be problematic because of the potential confusion between potale USP ethanol, and denatured ethanol, or even absolute ethanol, which contains traces of the benzene and acetone used to break the azeotrope (in many cases.) The consequences of consuming such nonpotables grades of ethanol can be, well, unfortunate.




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