Drunkguy
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"Sealed Tube"
On some reactions I have been reading it claims the reactants are mixed in a "sealed tube" and then heated.
Has anybody got experience with this?
An example is the organic syntheses preparation of what I call 4-cyclohexadione.
http://www.orgsynth.com/orgsyn/orgsyn/prepContent.asp?prep=c...
I'm not able to see any reason why the above compound cannot be prepared by hydrogenation of 1,4-benzoquinone, although it is not obvious how easily
this reduction can be accomplished inasmuch as the olefin FG's are conjugated with the keto FG's. Hydroquinone would be even harder to reduce because
it is aromatic.
Also with regard to the previous paragraph, is not the Birch reduction a synthetically useful way to get at interesting cyclohexane compounds?
My primary question relates to the thread title although I am keen to get any thoughtful advise and insight from skilled chemists with more experience
than I.
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YT2095
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I`ve only ever done a sealed tube rxn as a Getter, although the idea of using for other applications makes sense too, I`ve just never had cause to try
it, perhaps for making different Alotropes would be handy 
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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Nicodem
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Hydrogenation of p-bezoquinone yields only hydroquinone at normal conditions. Though with some catalysts it is possible to obtain
cyclohexanone from phenol hydrogenation (an industrial process), I think it is too far fetched to assume it would be possible to do something similar
with hydroquinone. But check the literature - otherwise you never know for sure.
The sealed tube technique was often used in the older times as a replacement for autoclaves, especially when using reagents very aggressive to the
autoclave coating (though today you have teflon coated autoclaves). Therefore today, practically no organic chemist uses it anymore - like I said,
using the autoclave is easier than glassblowing. Though sealing a tube requires no big skills.
The referred hydrolysis/decarboxylation is done in overheated water, thus requiring a closed vessel, but it can probably be done more or less
efficiently with basic hydrolysis, followed by heating of the resulting bis(beta-ketoacid) to >60°C for the decaboxylation step. But the authors
were more like: Why doing two steps if you can do one by using an closed reaction vessel?
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
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syntelman
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I am unsure if you by "sealed tube" really mean a sealed tube/ampoule? The Org. Syn. preparation is performed in a sealed vessel in order to elevate
the pressure.
Selectively reducing the double bonds in 1,4-benzoquinone may work with a suitable catalyst, but probably requires some careful planning. Oxidation of
1,4-cyclohexanediol is a more common way of preparing the afformentioned compound.
The Birch reduction is commonly used to prepare cyclohexaDIENES and is as such unrelated to the preparation of cyclohexanes.
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Nicodem
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Indeed, considering the batch size, I certainly concluded wrongly that they we talk about a sealed ampule. Checking the link I could find no mention
of "sealed tube". They used a 1.5 L autoclave instead.
| Quote: | Originally posted by syntelman
The Birch reduction is commonly used to prepare cyclohexaDIENES and is as such unrelated to the preparation of cyclohexanes. |
Yes, but performing a Birch reduction on p-dimethoxybenzene, followed by the mild acidic hydrolysis of the formed
1,4-dimethoxycyclohexa-1,4-diene would give the desired end product (though quite irrationaly more demanding when compared to the Org. synth. method).
At least I think this is what Drunkguy had in mind.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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YT2095
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just out of curiosity, and a little OT, but if I`m understanding this correctly, would cyclohexa 1,3,5 Triene, actually be Benzene?
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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syntelman
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Nicodem: Yes, you are right! Didn't think of that.
YT2095: It depends on how you see it. Cyclohexa-1,3,5-triene is a correct name for the Kekule representation of benzene, but as the electrons are
delocalized, benzene isn't actually cyclohexa-1,3,5-triene. 
[Edited on 20-12-2007 by syntelman]
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Drunkguy
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Thanks guys. This chemical is commerically available at not particularly inflated cost but the synthesis looks quite instructive rather than just
being loose with the wallet and letting somebody else make the effort while I sit infront of the TV.
Infact, on closer examination of that paper, it does say in the notes section that there are alternative ways to do the last step. After I first read
about the decarboxylation method several months ago, defeatism got the better of me and almost like my brain hitting a brick wall I decided not to try
and think about it.
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solo
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Have you checked this thread.......solo
https://sciencemadness.org/talk/viewthread.php?tid=8900
Shot with FinePix2650 at 2007-07-28
It's better to die on your feet, than live on your knees....Emiliano Zapata.
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Drunkguy
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I'm not that experienced with chemistry that I would be able to follow the discussion in the above linked thread.
As stated already in the recent thread on hydrogenation, my preliminary aim is to purchase a lecture cylinder of hydrogen and to do the method I used
in university that uses a balloon of hydrogen and the reduction/s are done under standard conditions.
Suffice to say, the technique I will be using is only enough to reduce styrene and is not strong enough to reduce a nitro group directly. However, it
is good building blocks and I have to use that as a "stepping stone" before I can raise my game to the likes of evil lurker.
I have a masters in chemistry although I graduated 3.5 years ago. My aim for 2008 is to finally get a commercial address and my first year plan is to
make enough money to cover my expenses.
[Edited on 23-12-2007 by Drunkguy]
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