tag:blogger.com,1999:blog-4387100009341358284.post7536021852693417698..comments2024-03-12T09:55:15.923+01:00Comments on Curly Arrow: Anhydrous Solvents Part 2: The THF Still - Do's and Don'tsDaniel Sejerhttp://www.blogger.com/profile/12498255536497699232noreply@blogger.comBlogger20125tag:blogger.com,1999:blog-4387100009341358284.post-83883596208005595472009-09-17T05:11:24.754+02:002009-09-17T05:11:24.754+02:00we have spare always dried rbf for THF still. Just...we have spare always dried rbf for THF still. Just in case we need to quench still (Na) then we replace it with spare new one.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-4387100009341358284.post-26921033654725701062008-09-26T20:57:00.000+02:002008-09-26T20:57:00.000+02:00I have heard that the potassium is much superior t...I have heard that the potassium is much superior to sodium, both in terms of efficancy and handling. Since it melts at the boiling point of THF it always provides a clean active surface. No need for cutting or pressing, just add a lump of metal. Moreover, after cooling it form a single lump that can be fished out prior to clean up of the still, no need for dangerous quenching. Fish it out and addAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-4387100009341358284.post-20217851265126823492008-09-25T19:51:00.000+02:002008-09-25T19:51:00.000+02:00I agree that a communal THF still is potentially d...I agree that a communal THF still is potentially dangerous if set up wrong and no one decommissions it regularly.<BR/>I always use Na dispersion in oil now with good pre-dried THF.<BR/>Fisher HPLC grade THF is pretty dry to start with. A 2/3 full 2 L still with approx 5 g Na/oil starts off green/blue and is that lovely purple colour after a couple of hours refluxing and ready to use. The best mikehttps://www.blogger.com/profile/08569978587044366289noreply@blogger.comtag:blogger.com,1999:blog-4387100009341358284.post-50104389276077924012008-09-24T20:59:00.000+02:002008-09-24T20:59:00.000+02:00we have a SPS here but the THF from it is dodgy. ...we have a SPS here but the THF from it is dodgy. THF will also polymerise on the column and break the solvent system, so, in my experience (requiring properly dry, not organic dry, solvents, as I'm an organometallic chemist) still-dried THF is still necessary.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-4387100009341358284.post-36343378270339577302008-09-18T09:32:00.000+02:002008-09-18T09:32:00.000+02:00Cool, rich kids would be more accurate. Many depar...Cool, rich kids would be more accurate. Many departments simply don't have the money for a Solvent Purification Systsem (SPS). Personally, I would love to have a SPS and ultimately everyone will be using these systems. If the safety people at Universities around the world would go to the Heads of Departments, Vice Chancellors etc. and compare the cost of SPS to rebuilding a burnt out Chemistry Daniel Sejerhttps://www.blogger.com/profile/12498255536497699232noreply@blogger.comtag:blogger.com,1999:blog-4387100009341358284.post-14435539202187118602008-09-17T23:46:00.000+02:002008-09-17T23:46:00.000+02:00I don't know what all the fuss is about...we cool ...I don't know what all the fuss is about...we cool kids use Grubbs-type solvent systems. I think it's way safer, although I suppose you might argue about whether it's the same quality solvent. At my school, we replaced all our alkali metal-based stills with the columns. We still use stills for amine bases and such, but it's typically calcium hydride.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-4387100009341358284.post-47507059268894589662008-09-15T11:25:00.000+02:002008-09-15T11:25:00.000+02:00I think the idea with Na dispersion is great and I...I think the idea with Na dispersion is great and I will probably switch ot it from now on.<BR/>But if you don't have Na dispersion, one guy taught me to add a few pieces of "soft" glass (from Pasteur pipettes) and a stirrer to the still. It scratches sodium and almost does not scratch the flask. So, if I set up the still today and need to get blue ether,THF or benzene tomorrow in the morning, I Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-4387100009341358284.post-54594460160708013852008-09-15T08:08:00.000+02:002008-09-15T08:08:00.000+02:00here's a nasty mistake i saw. some kook was visit...here's a nasty mistake i saw. some kook was visiting our lab and decided to use a clamp to close off the hose that connected his N2 line after he was done distilling. i don't know what he was thinking (maybe he wanted to get solvent out of it later???) but the next time he went to distill toulene, he forgot that the line was clamped and funny thing about a closed systems like that is will Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-4387100009341358284.post-46052152453299938122008-09-09T12:28:00.000+02:002008-09-09T12:28:00.000+02:00I would buy a good grad of NaNH2 from Acros, conde...I would buy a good grad of NaNH2 from Acros, condense some NH3 from a tank to it and there you go.<BR/><BR/>If you do it ftom Na and liq NH3 and Fe(III) catalyst you dont need any dispersion, Na chunks dssolve in NH3(l) quite fast. I am sure if you search sodium amide in Org Syn you will get a reliable, detailed write up. Dont modify it.milkshakehttps://www.blogger.com/profile/08188961610554710616noreply@blogger.comtag:blogger.com,1999:blog-4387100009341358284.post-33090558753746262782008-09-09T03:10:00.000+02:002008-09-09T03:10:00.000+02:00This Na dispersion in paraffin is interesting. Ca...This Na dispersion in paraffin is interesting. Can you use it to make sodamide? Or is commercial grade sodamide perfectly acceptable? I want to take 2-pentynoic acid to 3-pentynoic acid through the dianion. Apparently, when it reprotonates, it's almost exclusively as the 3-regioisomer. Supposedly you do it with 2 equivs NaNH2 in ammonia, but I must say I'm dreading this reaction.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-4387100009341358284.post-79063319001096108082008-09-07T21:08:00.000+02:002008-09-07T21:08:00.000+02:00That sodium wire doesn't last as long makes no sen...That sodium wire doesn't last as long makes no sense. Of course it does. It has to react to stop working. This is why sodium wire is great. It gets consumed so that when you regenerate the still you are less likely to have a fire. With wire you tend to use a lot less than by other methods which is why it appears to last for a shorter time. Just add a bit more after a few months. How a sodium Daniel Sejerhttps://www.blogger.com/profile/12498255536497699232noreply@blogger.comtag:blogger.com,1999:blog-4387100009341358284.post-81341521751908390552008-09-07T04:57:00.000+02:002008-09-07T04:57:00.000+02:00Last year we changed our 5 Litre THF still 2 times...Last year we changed our 5 Litre THF still 2 times so each one lasts ~ 6 months if properly maintained.<BR/><BR/>Most important is pre-drying THF we use to fill it up with. <BR/><BR/>We use sodium ribbon, our wire press always gets clogged up. Plus in my experince the wire does not last as longAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-4387100009341358284.post-70448796879402256272008-09-02T07:43:00.000+02:002008-09-02T07:43:00.000+02:00we have been using Na dispersion in paraffin wax -...we have been using Na dispersion in paraffin wax - it is commercially available (from Fluka, or it can be made very easily), it cuts with a knife like a chocolate without fire hazzard and due to huge surface area the benzophenone ketyl color develops promptly, with one hour. The wax does not distill over and the added benefit is that if someone forgets to re-fill the stil there is leftover wax tomilkshakehttps://www.blogger.com/profile/08188961610554710616noreply@blogger.comtag:blogger.com,1999:blog-4387100009341358284.post-13007445298590676842008-09-01T21:42:00.000+02:002008-09-01T21:42:00.000+02:00Rifleman, I can't really take credit for the still...Rifleman, I can't really take credit for the still. I only started working here in July. In fact I would have constructed it differently but it works and it is closely monitored so there is no problems. Only three people are allowed to turn the still on and off to prevent problems. Not that I know for sure but I assume that the pearshaped flask is just to keep things fairly dry in there and to Daniel Sejerhttps://www.blogger.com/profile/12498255536497699232noreply@blogger.comtag:blogger.com,1999:blog-4387100009341358284.post-69632413069852697552008-09-01T21:31:00.000+02:002008-09-01T21:31:00.000+02:00I just noticed your picture close up. Nice idea ab...I just noticed your picture close up. Nice idea about your receiver - it's now impossible to heat to dryness! We used a modified pressure-equalizing addition funnel, which afforded no such protection.<BR/><BR/>How do you fill the pear-shaped flask? It seems that the solvent will flood the stopcock, and without a way to relieve the pressure, the flow will quickly stop. Also, how do you dry the andreewhttps://www.blogger.com/profile/11618261795512988288noreply@blogger.comtag:blogger.com,1999:blog-4387100009341358284.post-6011622091278191852008-09-01T20:59:00.000+02:002008-09-01T20:59:00.000+02:00Rifleman, thanks for taking the time for your exte...Rifleman, thanks for taking the time for your extensive contribution. There are many variables. The most critical is the users. Are they responsible or not? Some places there will be countless users on several floors and not leaving it unattended becomes impossible. In fact not forgetting about it completely can become difficult if you haven't been using it yourself for a long time.<BR/>- I have Daniel Sejerhttps://www.blogger.com/profile/12498255536497699232noreply@blogger.comtag:blogger.com,1999:blog-4387100009341358284.post-28620955760036354332008-09-01T20:45:00.000+02:002008-09-01T20:45:00.000+02:00One alternative I've seen, to sodium wire, is to c...One alternative I've seen, to sodium wire, is to cut chunks of sodium, put it in a clean plastic bag, and mash it into thin flakes with a mallet. If desired, cut them into ribbons using a pair of scissors, and you're done. In comparison, this method is much faster than turning the crank on the sodium press.andreewhttps://www.blogger.com/profile/11618261795512988288noreply@blogger.comtag:blogger.com,1999:blog-4387100009341358284.post-42279365209846809882008-09-01T20:36:00.000+02:002008-09-01T20:36:00.000+02:00Bunsen Honeydew, if you don't have a sodium press ...Bunsen Honeydew, if you don't have a sodium press then I believe that you will have to cut sodium pieces of with a knife. One place I worked they had a metal rolling pin that they would use to make really thin sodium sheets. Nothing really beats the sodium wire I'm afraid. D!Daniel Sejerhttps://www.blogger.com/profile/12498255536497699232noreply@blogger.comtag:blogger.com,1999:blog-4387100009341358284.post-82806012869509081152008-09-01T18:10:00.000+02:002008-09-01T18:10:00.000+02:00Hmm... my lab's old THF still was set up similarly...Hmm... my lab's old THF still was set up similarly, but we had somewhat different procedures. It's been running for years without any mishap, and I feel strongly there are other ways of doing it safely.<BR/><BR/>We NEVER left the THF still unattended. That is the most important safety control, IMHO. Whenever it was used, the operator was always checking on it every now and again. <BR/><BR/>andreewhttps://www.blogger.com/profile/11618261795512988288noreply@blogger.comtag:blogger.com,1999:blog-4387100009341358284.post-79017336615831332092008-09-01T16:49:00.000+02:002008-09-01T16:49:00.000+02:00Great topic for a post. The one thing I have not b...Great topic for a post. The one thing I have not been able to find is a sodium press. Any suggestions?Anonymousnoreply@blogger.com