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Author: Subject: MTBE good substitute for Et2O?
Jor
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[*] posted on 22-4-2008 at 06:30
MTBE good substitute for Et2O?


I was thinking about buying some ether, for some organic reactions, but also forcing salts out of solution. However, i dont have a fume hood , and I would hate to mess with diethyl ether's high votality and flammability. Besides the cheapest lab-grade or better ether I can find is 22 EUR per liter from Carl Roth. Not to talk about peroxides...

Now, I saw an alternative. Methyl tert-butyl ether. 12 EUR per liter. How would this substitute diethyl ether? Its less volatile and its even more apolar as far as I know. Also less flammable and much less intention to form peroxides. This sounds ideal. before I buy this, are there any disadvantages considering MTBE?

Thanks, Joris
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not_important
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[*] posted on 22-4-2008 at 07:20


MTBE doesn't work well for Grignard and similar reactions, it doesn't coordinate as well with magnesium as diethyl ether, often you have to initiate the reaction in a more active ether and then slowly add MTBE and more reagent.

I believe that it is significantly easier to cleave MTBE under acidic conditions that diethyl ether, the t-Bu popping off fairly easily, so some reactions may not work as expected in MTBE.
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Jor
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[*] posted on 22-4-2008 at 07:22


Im not plannig to do a grignard synthesis anywhere soon.
MBTE is less stable in acidic conditions. Good to know. Any other major differences? Because if this is all, it will be ordered today.
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[*] posted on 22-4-2008 at 08:12


I have at least one organic chem lab textbook that specifically recommends MTBE as a replacement for Et2O, citing the lower volatility and lower peroxide hazard as reasons it is considerably safer.

The book does mention that MTBE is not good for Grignards, you need the usual ethers for those, but otherwise MTBE is a fine and recommended replacement.
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Jor
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[*] posted on 22-4-2008 at 09:16


Ok, will buy it then.

One last concern. I know MTBE is less likely to quikly form peroxides. But even then, I do everything small scale. So 1Liter of this ether is going to last me for very long. There are no stabilisers in the MTBE (Carl Roth, for synthesis)

My question was, should I stabilise this myself, or should I just dispose of it after x time (if yes , whats x?).
How could it be stabilised? Somewhere I thought I have read ethanol can be used to stabilise diethyl ether. Not sure. Could this be apllied for MTBE as well?
And how about diphenylamine? I heard this could be used as a stabiliser for something. Forgot for what. I have 100g of this.

Google doesnt yield great results. All im getting is sites about fuel composition and drinking water tast...

Thanks
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Klute
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[*] posted on 22-4-2008 at 09:35


I think phenols like hydroquinone, p-methoxyphenol, etc can be used as stabilizers for ethers.
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[*] posted on 22-4-2008 at 09:48


Let's see, I've heard of the iodine test to check peroxide levels, and I've seen ethanol and BHT (butylated hydroxytoluene, i.e. 4-methyl-2,6-di-tert-butyl phenol) on labels. I would assume many antioxidants will suffice, such as Klute suggests, as well as food additives such as vitamins A or C, etc.

Tim




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[*] posted on 22-4-2008 at 09:54


I stabilize my ethers (Et2O, THF) with BHT which I bought off the internet. It seems to work OK. I test my ethers periodically with iodine for peroxides and the results come up negative.

Lyondell, a manufacturer of industrial quantities of THF uses BHT and that is where I got the idea to use it.

[Edited on 22-4-2008 by Magpie]

[Edited on 22-4-2008 by Magpie]
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[*] posted on 22-4-2008 at 10:13


Ethers bought from chemical suppliers do not have to be stabilized, they already are. And MTBE does not form peroxides at all, that's the good thing about it! It is delivered unstabilized and may remain that way.

MTBE does have some disadvantages that disqualify it as a good substitute for Et2O.
The first one is its high solubility in water. Water also has a high solubility in MTBE. Check out the literature values.
The second one is its really bad behavior towards acids. It is cleaved so easily that it can't be used to extract aqueous solutions if their pH value is much lower than 7. If it is shaken with an aqueous acid, it is cleaved to methanol and isobutene, and the latter forms some oligomers, which are resinous products that contaminate any extraction you do.

And of course its unsuitability as a grignard solvent, as already mentioned!

[Edited on 22-4-2008 by garage chemist]




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[*] posted on 22-4-2008 at 10:15


Of the named chemicals by Tim and Klute, I have ethanol (duh) and hydroquinone. I do not feel like buying a stabiliser.
How much stabiliser should I add? 1 mL ethanol per liter MTBE?
Or how much hydroquinone? 1 gram per liter?
And would diphenylamine work? Im sorry for the beginner questions, but I'm quite scared of peroxides, so want to stabilise it, but dont want to ruin my MTBE. So which of these would you recommend, and what quantity?
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[*] posted on 22-4-2008 at 10:22


"And MTBE does not form peroxides at all, that's the good thing about it! It is delivered unstabilized and may remain that way."

If this is, indeed true then you need not worry.




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[*] posted on 22-4-2008 at 10:29


Jor, our posts have been written at nearly exactly the same time and yours appeared below mine although at the time I write mine yours had not been written. Have you read what I had to say?



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[*] posted on 22-4-2008 at 11:21


Yes I have read.
You say MTBE solubility in water is quite high. I wonder why you said that, because Et2O dissolves approx 6 grams per 100mL H2O, while MTBE dissolves 4,8 gram per 100mL H2O, at least according to JTBaker.
A problem might be the fact that it cant withstand acid. About what pH are we talking, where it will cleave significantly?

I now also have an option of buying Diethyl ether (just found it 5 mins ago.). 13,20 per liter. This is not stabilised as far as I know, it not in the product info.
I am considering buying this, but I want to know first how much stabiliser I shoud add.
Isnt a few ppm anough? At least I thought it was enough when using BHT. I dont have BHT.
Options could be (?) :
ethanol, hydroquinone, diphenylamine (can this be used or not? i thought garage chemist told me this was an useful stabiliser, but I dont remember for what exactly). Wheat quantities should be added to a liter? milligrams or even grams?

And magpie, I assume you mean you test with KI?
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[*] posted on 22-4-2008 at 11:53


Even if the label does not say it is stabilized, this does not mean that it is not stabilized. I have purchased a Tendo 1-liter ether, which is (more or less) OTC. The bottle does not mention anything about the contents, it is just labeled "Tendo's ether". But because it is sold OTC and many non-chemist consumers will buy this product, it MUST be stabilized, otherwise there would be numerous accidents with people not knowing anything about ethers and peroxide formation. The only thing the general consumer needs to know about the ether is that it is highly flammable.



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[*] posted on 22-4-2008 at 11:55


Yes, Jor, KI. Lyondell uses 200ppm BHT in their THF. You can read more at:

http://sciencemadness.org/talk/viewthread.php?tid=2437&p...
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[*] posted on 22-4-2008 at 13:33


Diphenylamine is a very efficient stabilizer. 20ppm is enough with it. This is one of the best stabilizers you can use.

About the solubility in water, I'll have to check. I was using information from Ullmanns, and I think it listed the solubility higher than that of Et2O.

I also doubt that the cheap ether is unstabilized! If unstabilized, it will tell so explicitly on the label and in the catalogue!




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[*] posted on 23-4-2008 at 00:00


You can only buy unstabilized diethyl ether if you specify it (for use in HPLC and similar), otherwise all diethyl ether on the market is stabilized (usually with at least 1 ppm BHT).
MTBE does not come stabilized as far as I know, since there is no reason for it.
Chloroform is the most problematic in regard of stabilizator's presence since it requires an annoying method for removing the ethanol most commonly used as decomposition inhibitor (and some reactions require ethanol free chloroform). Other solvents generally contain stabilizators that don't interfere with most reaction.
The water solubility of MTBE is apparently 4.2 g per 100 ml water at 25°C (though there is confusing data about this, see: http://www.efoa.org/mtbe/pdf/appendix1.pdf; for comparison, the Wikipedia entry for Et2O claims its solubility 6.9 g per 100 ml water).




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[*] posted on 23-4-2008 at 12:52


I agree with garage chemist, Diphenylamine is a very good stabilizer. To all my ethers I added 5-10 ppm (or less), thats enough for many years. It has the advantage not to react with sodium metal or KOH like phenolic stabilizers do that (uneffective phenolates are formed). So you can dry diethyl ether, THF or another ether with these drying agents and the ethers remain stabilized.

[Edited on 23-4-2008 by grind]
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[*] posted on 24-4-2008 at 12:09


Additional info:

"Stabilizers

Examples of stabilizers for inhibiting peroxide
formation are hydroquinone, 3,5-di-tert-butyl-
4-hydroxytoluene (BHT) and butylated
hydroxyanisole (BHA). Usually, proportions
on the order of 250 mg/kg suffice to ensure
stability during normal circumstances.
However, although stabilizers slow down
peroxide formation in THF, they do not
prevent it completely. And once a peroxide
has been formed, the initiation of radical
reactions may proceed.
These stabilizers have high boiling points,
and thus remain in the bottoms residue
following any distillation. Consequently, the
distillate must be restabilized if required.
(Note that these stabilizers have an
unpleasant odor that may persist after the
tetrahydrofuran has evaporated.)"

From the very interesting and complete THF Brochure
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[*] posted on 6-9-2015 at 09:04


Regarding use for Grignards, I have run these using THF, about 2 moles per g. atom Mg, in toluene. This mixture was easier to dry than neat THF. I expect adding quite a small amount of THF to tBME would make it usable for these, and some other organometallic preps.
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[*] posted on 6-9-2015 at 13:12


chemretd, to prepare grignard in TBME you need to follow a regular procedure for benzene/toluene/other solvents that don't solvate grignard reagents - first use a solvating ether (diethyl, THF), then exchange it with anything else.
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[*] posted on 6-9-2015 at 21:26


Instead of stabilizer some ether was sold in copper cans.
I don't know if it is still sold this way but copper acts as a catalyst to destroy peroxides.
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[*] posted on 8-9-2015 at 16:59


Many process chemistry units use MTBE as a replacement for ether in extractions and some reactions due to its lower flash point, higher BP, and lower peroxide formation. It works well in most cases, except for Grignards as noted, but otherwise is pretty good. Likewise, many development groups use toluene or xylene instead of benzene, and heptanes instead of hexanes. The higher BP would not be an issue for most home chemists, but can be a pain for rotovaps, as it is a little llower to come off in some cases, unless you have a good vacuum. Ether, THF and MTBE all have some water solubility, but it is manageable.
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