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Author: Subject: Diethyl Ether - Illustrated Practical Guide
len1
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[*] posted on 4-1-2008 at 18:25
Diethyl Ether - Illustrated Practical Guide


This is a series of Illustrated Key Syntheses in Chemistry which I intend to post, with the purposes and guidelines outlined in the thread of the same name in the General Chemistry section.
I shall attampt to ensure that the first post in all syntheses contains all the relevant information. If something needs to be added later on, due to comments further down the thread for instance, I shall edit the first post.




Aim


It is the aim here to present an illustrated demonstration and comparison of two simple methods for generating and purifying diethyl ether suitable for the amateur. The yield of the main product and impurities are analysed using analytical techniques and FTIR. A misconception associated with the role of sulphuric acid in ether generation is illustrated, and this should allow to increase yield.

Motivation


Ether is a key compound in organic synthesis. Arguably the first anaesthetic used, nowadays its major use is as a solvent, a fuel, in extraction and purification, and for anhydrous reactions such as Grignard synethesis. Its synthesis by H2SO4 catallytic dehydration of ethanol is described in many organic practicums, however the yields and reaction rates are rather low - the combined volume of EtOH and H2SO4 produces 1/4 the volume of ether - which brings into question its suitability as a preparative method for volumes required in the laboratory. An alternative source of ether easily accessible to the amateur takes the form of fractioning of starting fluid, whose ether content ranges from 25 - 60%. There is a paucity of data on the efficiency of this method, and the purity of the product so obtained, and this report presents a quantitative evaluation, and comparison to ether obtained via the first method, for the least favourable 25% starter fluid. Some experimentation along these lines has already been presented in this forum in the Making Diethyl Ether and Ethyl Ether Distillation and Synthesis threads. The present is an extention of these, with an improved procedure, analysis, and illustrations.

Findings


The ethanol dehydration reaction is unsteady (non-smooth), time intensive, but is cheap, and can give good yields.

  1. Yield 74% based on theoretical and 40% based on ethanol consumption
  2. Ethanol based yield will tend to theoretical yield for larger runs
  3. Reaction temperature of 140C is way above b.p. of EtOH leading to bumping
  4. Instability, hard to establish correct EtOH drip rate and steady-state conditions
  5. Almost all H2O formed distills with ether - minimum 4 purification steps required
  6. 12% EtOH distills unreacted - requiring corresponding amounts of CaCl2 for purification
  7. Clear FTIR spectrum of product

Fractionation of starter fluid, is quick, efficient, product purity is comparable to the above - but it is expensive

  1. 76% yield of available ether using 25% ether starting mixture
  2. Fast, single step procedure
  3. H2O contamination evident in FTIR spectrum due to lack of purification - irrelevant for many extractions



Theory


Et-O-Et from dehydration of EtOH

  1. C2H5OH + HHSO4 -> C2H5HSO4 + H2O

    This is an acid base reaction in which sulphuric acid forms the ester ethyl bisulphate and generates water. This reaction occurs in the cold immediately when the reagents are mixed, evolving much heat. For this reason its best to start with the reagents near freezing. This step forms the main 'overhead' wastage of alcohol in this synthesis, since the alcohol remains bound and very little ether is generated. Note that H2O is generated in this reaction in a 1:1 ratio to the H2SO4 used. Thus, contrary to what is often stated, one does not require absolute alcohol, or 98% acid for the reaction to work. The main requirement is that the combined initial reagent water should not make the initial H2SO4 concentration less than about 70%, at which point the boiling point of the mixed acid approaches the reaction temperature used in step 2 - and it will start distilling over with the products.

  2. C2H5HSO4 + HOC2H5 -> C2H5OC2H5 + H2SO4

    When excess EtOH is added to the mixture in (1) and heated to 140C ether if formed and H2SO4 regenerated - it thereby acts as a catalyst. If no excess ethanol is added, the ethyl bisulphate remains stable to about 160C when it starts eliminating H2SO4 and generating ethylene C2H4. It is therefore imperitive that this temperature is never reached during the reaction. Instead, ethanol is dripped in at the rate at which it is converted to ether - two moles for every mole of ether formed, while the composition of the reagent fluid remains esentially that of (1). The H2SO4 liberated regenerates ethyl bisulphate with the extra alcohol added.

    The vapour pressure of water above 75% H2SO4 is about 0.4 atmosphere at the reaction temperature, hence it is distilled over with the ether as soon as it is formed. Its concentration in (1) does not rise substantially during the reaction - the acid acts as a catalyst not as a dehydrating agent as is often quoted. Therefore a little acid can produce quite a lot of ether - the limiting factor coming from oxidation-reduction side reactions, which remove H2SO4 from solution, and result in the contents of the reagent flask becoming tarry.

Method

All reactions were carried out at an ambient temperature of 42C


Formation of crude ether

The first stage is to carry out reaction (1). 20gms of clean sand were placed at the bottom of a 1L 3-neck flask, and 180ml of EtOH (sold as methylated spirit, about 95% EtOH) were poured in through a funnel. Next 160ml of 92% (1.81 sp) H2SO4 technical grade were measured out, and cooled, together with the EtOH, in a freezer. The H2SO4 was then poured into the flask gradually and with frequent mixing - so the mixture attained homogeneity before the next lot was added. This took about 5 mins, during which time the temperature of the mixture rose to about 60C. The flask was fitted with a high-T thermometer, which dipped right to the sand, as well as an adaptor for measuring the exiting vapour temperature and an outlet leading to a cooled-coil condenser. The vertial neck was fitted with a tube for delivering the EtOH right to the bottom of the reagent mixture, Figure 1. This is necessary as the temperature at which ether is generated is well above the bp of EtOH. If dripped onto the surface of the reaction mixture most will vapourise before reacting, introducing it below the surface affords better mixing - as evidenced by only 12% EtOH distilling unreacted in the procedure. However the generation of superheated ethanol vapour is a major source of instability, and leads to difficulty in controlling the reaction.

The receiver end is equiped with a secondary IR condenser, whose outlet dips through a delivery tube into an ice/water mixture, figure 2. The exit from the delivery tube is vented. The secondary condenser is cooled by a small submerged 2.5W motor, circulating the freezing water through its jacket. A secondary condenser is best employed to condense ether - which forms explosive mixtures with air - on hot days. Since the ambient temperature in the lab was 42C (108F) ether would be a gas, and for the same reason tap water (30C) would not be efficient at condensing ether on such a day. However a tap-water cooled condenser was used ahead of the ice-chilled stage to cool the 70C vapour from the reaction and extend the life of the ice bath.



Once the equipment had equilibrated, the mixture was heated on a heating mantle to about 140C, when some gas evolution (bubbling) commenced. At this point 200ml EtOH was added to the drop-funnel and the delivery rate adjusted so the flow rate in the delivery tube was about 3mm/sec, at which rate the entire volume is added in about 2 hrs. The delivery is accompanied by some unavoidable bumping due to the superheated ethanol, this periodically shakes the reaction vessel contents, and introduces frothing, figure 3. The bumping can not be eliminated altogether, but it can be adjusted to acceptable levels by keeping the EtOH delivery rate below the above mentioned, the rate can be gauged by bubbles in the delivery tube introduced by the bumping. The temperature of the reaction bath stays at a remarkably steady 140-145C due to the thermal equilibrium introduced by the reaction - the distilling ether and water removes heat which prevents the temperature rising. The temperature of the evolved ether/H2O vapour kept at a fairly steady 60-70C. One can see the ether distilling with the water in the exit tube, figure 4.



Reaction analysis

When all the EtOH had dripped into solution (~2hrs) the tap was closed and a temperature of 140C was maintained until the ether flow rate into the receiving flask had curtailed (about 10mins). At this point the appartus was cooled down. The remnants in the reagent flask are seen in figure 5. The black colour is due to oxidative side reactions producing carboneous mater, but there were no solid lumps, and the products of these reactions were more obvious by appearance than by their volume.

The reaction mixture, 240ml, was titrated with NaOH solution and found to be 69% H2SO4 by weight. This represents a loss of 20gms H2SO4 - presumably as SO2 in the oxidative reactions which produced the tar. The density of the reaction mixture was 1.48, compared to 1.46 for ethyl bisulphate and 1.58 for 69% H2SO4. Assuming a linear ethyl bisulphate/water density-concentration curve, we see that the remnant reaction mixture is mainly ethyl bisulphate, with the water present 21gms, being essentially that of the initial acid. In addition the mass concentration of H2SO4 in the initial ethyl bisulphate solution is 98/(98+46) = 68%. We thus come to the conclusion that the reagent mixture remained eseentially unchanged during the reaction except for the loss of 21gms of H2SO4 to oxidation/reduction processes.

The main drawback of this reaction is the need to renew the spent H2SO4/EtOH reaction bath, which forms a waste in the process. The present findings show that the reaction bath being mainly unchanged, is suitable for coninued use. The attrition, 21gms H2SO4 is a fraction of the 240gms H2SO4 still remaining. It is likely the bath can be used for four-fold the volume of EtOH used in the present experiment (indeed this is consistent with the finding of the inventor of the process - a little H2SO4 goes a long way). A further limiting factor is likely to be the build up of tar in the flask, hindering the reaction.

Purification, yield

Figure 6 shows the contents of the receiver flask, 210 ml single layer. The content were poured into a separation funnel, 100ml of 10% NaOH solution added, and shaken, figure 7. The aqueous layer was removed, and the process repeated. This left 182 ml ethereal product in the funnel, while the aqueous layer correspondingly gained 28ml, where the second washing gained only 3ml showing this purification was essentially complete. Ether is 10% soluble in water (presence of EtOH enhances this), and this washing removed mostly H2O (with SO2 and ethanol being minor impurities removed). This result is in accord with the fact that 200ml of EtOH (3.4mol) produce 30gms of water according to reactions (1, 2) (recall that the initial 180ml remained essentially unchanged).



Next 26gms fused and crushed CaCl2 were placed in a flask, cooled, the ethereal layer poured in, and let to stand 1hr in the cold. The flask was then placed in a water bath maintained at 60C, and the fraction boiling in the range 35-39C collected, figure 8. This left the flask almost entirely dry - showing most water and ethanol have been removed by the washing and the CaCl2. The latter gained 18gms in the process, which is more than the desired maximum 40% CaCl2 : EtOH ratio, hence we conclude 50gms fused CaCl2 per 200ml crude is the appropriate ratio in this setup. The adduct can be seen in figure 9.



The product was analysed on an FTIR machine (see the thread http://www.sciencemadness.org/talk/viewthread.php?tid=7993&p...) in both thick and thin film, and gave very good spectra, figure 10. The presence of traces of H2O and EtOH are evident, and this can be removed with the appropriate amount of CaCl2. The final purified product occupied 130ml (1.26mol), figure 11. The corresponding yields are as follows:

  1. Based on 200ml (3.4mol) EtOH, 74%
  2. Based on total EtOH 380ml (6.4mol) 40%


Clearly continuation of the reaction will get the yield closer to (1).






Fractionation of starting fluid

A 493ml pressurised can of starting fluid, with 25% ether, and dimethyl ether as propellant was used. Both the can and a 1L receiver flask were cooled to 0C before the contents of the can were emptied via a tube, while maintaining both containers in a freezing bath. This produced only 390ml of fluid, and it was presumed that most of the ether was lost at this stage due to its co-vapourisation with the dimethyl ether. To overcome this, the arrangement shown in figure 12 was employed. In this way 430ml were gathered - it is assumed the 493ml contents quoted on the can includes the dimethyl ether propelant.

Some boiling chips were dropped into the flask, and fractionation on an insulated hempel collumn with a hot water bath was performed, figure 13. The boiling commenced right away - but it wasnt allowed to be too rapid - a feat which can be accomplished by lowering and raising the water bath - and in about 10 mins the first drops of fluid appeared in the condenser. The fraction boiling in the range 33-39C was gathered, which took about 90mins. The volume of this fraction was 83ml, or 19% of the total liquid volume. This gives a 76% yield in the separation on the 25% total ether content quoted. Figure 14 shows a thick film spectrum for both this fraction, and that of the previous synthsis, showing that a considerable amount of water is still present in the present product, due to lack of a purification step. This can be removed with CaCl2 as before, but for many extraction processes it is acceptable.







Conclusion


Acid-catalysed ethanol dehydration is an efficient and cheap method for ether production, giving a maximum yield of about 74% based on ethanol. With the present simple arrangement it is however enherently unstable and time consuming. Fractionation of strater fluid is a much faster simpler method, it is however more expensive.

[Edited on 8-1-2008 by len1]
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[*] posted on 4-1-2008 at 20:04


hmm.. Nicely done on this topic and the chlorine topic. Keep up the good work!
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[*] posted on 23-3-2008 at 02:25


Yeah, really damn good work. I really enjoy your posts



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[*] posted on 24-3-2008 at 21:09


Regarding the distillation of starting fluid:

I find it is best to use starting fluid which only uses CO2 as a propellant, I have encountered those which used isobutane and propane and noticed the ether distilled contained these dissolved gases. This could be seen by the fact that when this cold distillate was poured onto a paper towel, it fizzed on contact (like soda in a way).

Also if the starting fluid container does not have a spray nozzel tube attachment as yours does (I have never seen starting fluid sold with one) you can easily pull off the spray nozzel from the can, and attach soft plastic tubing to the the valve; and transfer in this way. I have heard of people (although I have never tried it) turning the can upside down and puncturing the bottom, releasing the compressed CO2 (in the head space above the ether) and then simply pouring the mixture out of the can.

I like your idea about chilling the can before sparying, I will try this in the future (although even spraying alone seems to cool the can quite a lot). I also can confirm similar yields, from the distillation of 6 cans of a 35% ether starting fluid I get about 650mL of ether (I collect from room temp to 35c as the forerun seems to be ether).

EDIT: When distilling ether I have noticed that connecting a tube to the vac adapter outlet and routing it out a window, makes the entire process of distilling ether nearly odor free.

[Edited on 24-3-2008 by smuv]
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[*] posted on 24-3-2008 at 22:20


nice work
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[*] posted on 2-5-2008 at 00:33


Great read once again!!! And you own an FTIR?? :o



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[*] posted on 2-5-2008 at 03:17


I think yield would be higher in the procedure I outlined compared to what you did because here ether distilation is accompanied by the flux of an uncondensable gas - this will carry some ether out of the apparatus with it, also makes distillation rate harder to control.

I do not think its so safe due to the higher rate of ether loss to the environment - but if there are no hot surfaces in the vicinity (ie youre using a mantle) and no flames I think you should be alright.

The FTIR is mine - but as Ive said elsewhere on this forum, theres no reason why amatuers shouldnt have one these days, they can be bought for several hundred dollars on eBay. Ive outlined the refurbishment I did on my FTIR elsewhere on the forum. Doing chemistry with compared to what it was like before feels like suddenly being able to see.

Same applies to MS and NMR, but the FTIR is the most useful of these for following reactions.
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[*] posted on 2-5-2008 at 07:25


Nice work again, Len.

When the industrial process was based on this method, they ran it continuously for weeks. Ethanol was added continuously, some water was distilled out as well, keeping the acid strength up, and separated from the ether through fractionation. This indicates that the acid should be reusable to some degree.

Other catalysts that have been used include H3PO4, which would be a mix of condensed phosphoric acids at the reaction temperature, and aromatic sulfonic acids. These cause less side reaction and charing, not oxidising the alcohol and thus releasing SO2; or at least that was claimed.
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[*] posted on 2-5-2008 at 10:51


Quote:

Is this safe? I was a little paranoid, I'm using an electric single element stove on a dimmer switch


Len, he didn't say a "mantle." Using a bare element in the presence of ether would make me nervous. I would preferably use a steam bath for ether, but have also used a mantle (fiberglass covered element).
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[*] posted on 11-8-2008 at 09:10


The 'start-you bastard' product used in your illustration Len utilises dimethyl ether as the propellant. If the cans are dropped to below -50C, they can be drilled through and decanted into a round bottom. A dry ice condenser will condense the dimethyl ether fraction that comes over at around -25C. This ether is easily re-stored in a small bbq gas cylinder. It is a very useful thing, forming up to 35%solutions with water.
From there the di-ethyl ether can be distilled and so on.
Just additional information nothing else.

In case any are in dispute of this fact, because on the can it actually states the propellant as being CO2, however if you download the MSDS on the product it states the propellant to be dimethyl ether. I have actually performed the reclaimation above and can tell you that dimethyl ether condensed, making the claim on the can incorrect and the claim in the msds correct. Another fine example of australian attention to detail, lol.

[Edited on 26-8-2008 by Panache]




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[*] posted on 4-7-2009 at 02:28


Thanks for this publication, it's very detailed and comprehensive. Good work! I've made two ~200ml batches of ether using your procedure, and yields are exactly as you described. However i have 2 small comments. First is that ether prepared from C2H5OH/H2SO4 and purified as you described contains some small ammount of water, boiling points are evident - final product start to destill at ~34C that corresponds to distillation of azeotropic mixture of ether with water containing 98.74% of ether (boiling point 34.15C). Second is that ether tends to accumulate peroxides durring distillation and they surely present in final product, to get rid of them it is very recomended to store final product above a small batch of KOH, it is insoluble in ether, transforms forming hydroperoxides to insolube products and also acts as good dehydrating agent.

[Edited on 5-7-2009 by Engager]




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[*] posted on 17-10-2009 at 10:43


Hey great work however I have a question. You used methylated spirits which contain (most of the time) a mixture of ethanol, methanol, and many other alcohols with ethanol comprising about 90% of the mixture. Do these 10% of impurities cause a problem in the synthesis? For example the boiling point of ethanol is 78C while the boiling point of methanol is lower at 65C and isopropyl alcohol being higher at 82C when you distill of the primary reaction leaving behind the black liquid wouldn't the alcohol distill over with the ethanol? If so do they react with the sulfuric acid forming a separate product? I really would like to replicate your work and I have a can of Denatured Alcohol but I am wondering how these other alcohols present with effect my product.
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[*] posted on 17-10-2009 at 15:32


len works in Australia where the denaturant is usually MIBK.If you use a mixture of alcohols,you will get a mixture of ethers.If you have significant methanol you will form significant dimethyl ether,which due to its very low boiling point will probably carry off a good deal of your target.(see Panache a couple of posts above)



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[*] posted on 22-12-2009 at 20:35


I liked this "Practical guide" so much that I have duplicated,( as best I could), the entire procedure with the exception of the FTIR results. I used Everclear ~191 proof for my source of EtOH rather than the SDA 200 because of its denaturing. Also I did run 750mL EtOH through the reaction bath confirming that it can convert quite a bit before needing to be replaced. Here I have include some pics.

Ether Synth.JPG - 54kB This is the first setup.

Raw ether small.JPG - 27kB This is the raw ether 655mL

Ether wash small.JPG - 41kB Washing the product.



Ether synth small.JPG - 56kB Re distilling from the CaCL2

Ether finished.JPG - 27kB Here it is, 320mL Diethyl Ether!


I really enjoyed the experiment. Thanks to Len1 for the "Illustrated Practical guide" !


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[*] posted on 22-12-2009 at 22:53


Nice work, Rabbit - thanks for the pictures. You have a lot of nice equipment. It is of sufficient scale for production of reagents. I'm in the process of acquiring some larger (24/40) scale equipment for that purpose.

Where did you get your equipment? EBay? Do you like the Graham condenser better than a West (Liebig style) condenser?




Knowing that I can buy good quality NaOH, HCl, and H2SO4 locally gives me great peace of mind.
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[*] posted on 23-12-2009 at 01:33


Very nice, I enjoyed your post. Thank you
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[*] posted on 23-12-2009 at 14:18


Let's make ether picture gallery! My equipment is not so perfect as western, but is much cheaper and works just fine =)

My ether setup:

Reflux flask setup:

Condensing ether vapors:

Crude ether:

Pure ether redestiller setup:

Final product - pure ether:



[Edited on 23-12-2009 by Engager]




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[*] posted on 23-12-2009 at 15:35


Very good! But because of its low boiling point, only 30ÂșC I believe (it gets that warm in my country in summer), and liability to form an explosive peroxide on exposure to air and light, you will have to keep it in a refrigerator, and preferably sealed under argon (or a gas that you are sure it will not react with or adversely affect any reactions in which it is used as a solvent or reagent).

[Edited on 25-12-09 by JohnWW]
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[*] posted on 23-12-2009 at 22:36


ne hueva!
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[*] posted on 24-12-2009 at 13:51


Quote: Originally posted by Magpie  
Nice work, Rabbit - thanks for the pictures. You have a lot of nice equipment. It is of sufficient scale for production of reagents. I'm in the process of acquiring some larger (24/40) scale equipment for that purpose.

Where did you get your equipment? EBay? Do you like the Graham condenser better than a West (Liebig style) condenser?



Thanks Magpie. Yeah, I do have quite a bit of glassware. Sometimes, I buy a new piece on ebay and when I go to put it away, I find that I already have one. Ooops! I bought some of my glassware on ebay, some I buy direct from Wilmad Labglass, and the rest I get from a glass shop I use for my custom pieces.

The condenser in the pic is not a Graham, it is a jacketed "cool coil". I feel that the Graham has too much flow resistance for a first stage. The cool coil works well and the jacket around it really makes the difference. It is basically a Liebig with a coil inside of it. The Graham may be better for the second stage but I like the effectiveness,(greater surface area), of the Friedrich. I bought the jacketed cool coil from Wilmad Labglass.

I really like to seeing the hands on work all of you guys have posted.

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[*] posted on 25-12-2009 at 03:33


JohnWW: bp of ether is a little higher, at ~35C. Storing it in the refrigerator is overkill unless you live somewhere rediculously hot. Peroxides arent that much of a problem if you keep the bottle topped up and store in an amber bottle, preferably stabilised with some BHT. There are many posts on ether peroxides and preventing their formation; copper supposedly does the job nicely, but requires a large surface area (a copper scourer stuffed into the bottle should be sufficiently adeqate. Alternatively you could form a copper mirror on the inside of the bottle, using chemical deposition. This can be done by electrolysis if you store your ether in aluminium bottles).

Argon is definately OTT, especially if you have limited headspace and an inhibitor.

[Edited on 25-12-2009 by DJF90]
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[*] posted on 25-12-2009 at 18:40


Wow! I am jealous of all this equipment!

But I wondered: does 'wet' ether form a peroxide also? Well, I suppose it is 'yes,' but I meant that perhaps it is destroyed by water, and so safer to store?... But anyway, copper sounds a very nice idea if it works well... I hadn't heard of that before. I would like to try this one day, so thank you for the details since it will, I hope, be very useful!:D
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[*] posted on 25-12-2009 at 19:42


I've seen ampules of hygroscopic liquids from sigma stored over copper shot/powder. I'm not sure how well simply taking a lump of copper or shavings would work, probably too dirty?

Also, doesn't storing over KOH precipitate any intermediate before the peroxide forms?
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[*] posted on 26-12-2009 at 01:13


Seems to me a transition metal would catalyze the reaction. Or is that more of an iron thing?

The usual solution is easy enough: the last bottle of ether I used claimed ethanol as a stabilizer. Add back a few drops of the swill you started with and all's well.

Tim




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[*] posted on 26-12-2009 at 05:21


I'm not sure why hygroscopic liquids were stored over copper aonomus; the function of the copper with ether is to inhibit the formation of the peroxide.

Tim: I think the role of the copper is to actually catalyse the decomposition of any peroxide that may form. Definately a good thing. I had a paper on it somewhere but cannot find it. I'm familiar with ethanol being used to stabilise chloroform but its use in ether is new to me. Thanks for sharing!
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