papaya
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acetone hydrogenation
Hi, while the topic may appear worthless I must say that to me it's easier(and cheaper) to obtain technical grade acetone rather than isopropanol, so
I like the idea of hydrogenation. I did UTFSE and didn't find this discussed before(sorry if it was), so : what way one must do it effectively? I did
2 small tests (few ml's scale) : trying to reduce acetone with Al+ dilute HCL; and the same with Al+ dilute NaOH. As an indicative of alcohol
formation both were tested for capability of isopropyl nitrite formation (with NaNO2 addition in acidified medium, the thing was NOT distilled
beforehand) - I could observe positive only in the case when NaOH+Al was used (though was tested only once - it may also work with acid). So the
quiestions: the acid or the base ? if acid - Al or other metals like Fe, Zn ? If the base - why won't work with acid? etc, etc..
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papaya
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I mean - do I need some special metal (Ni) added for catalysis or generally - what is the mechanism of such kind of reductions (hence the optimal
conditions), anybody ?
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Dariusrussell
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I second this topic as it seems interesting. You do need a catalyst, though I have no clue what an appropriate one would be (Platinum, Palladium,
Nickel?). It also looks like it needs to be done in an inert environment.
http://www.youtube.com/watch?v=Ngv-IFRGRXQ This might help you
http://www.youtube.com/watch?v=Ercr5SCIEnU
If anyone more experienced wants to chirp in please do so
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papaya
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Seems I have to try once more with Al/HCL, but for comparison do it with and without NiCl2 addition to see if there's any difference. Does this
belong to alkene hydrogenation (trough enol form) or hydrogen is added to C=O directly ? Now I even doubt that molecular hydrogen evolved has nothing
to do here.
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Nicodem
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The tittle says "acetone hydrogenation" yet you discuss reductions by metal dissolving reductions. It makes me wander, if you know what you are doing.
The hydrogenation of acetone was referenced in one thread.
The metal dissolving reductions of ketones to alcohols are well known and you can find plenty of examples in the literature, particularly in the
pre-borohydride literature. I'm not sure, as I never really reviewed the literature, but in the old times zinc or iron in acetic acid or
aqueous/alcoholic amalgamized aluminium were used. I can't see how aluminium with HCl could work - that would just produce a bunch of hydrogen rather
than do the reduction. On the other hand, zinc with HCl might work with acetone, provided the acid is added appropriately slowly. For zinc, it would
still be more reasonable to simply use acetic acid or NaOH(aq). Anyway, check the literature.
…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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papaya
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Quote: Originally posted by Nicodem  | The tittle says "acetone hydrogenation" yet you discuss reductions by metal dissolving reductions. It makes me wander, if you know what you are doing.
The hydrogenation of acetone was referenced in one thread.
The metal dissolving reductions of ketones to alcohols are well known and you can find plenty of examples in the literature, particularly in the
pre-borohydride literature. I'm not sure, as I never really reviewed the literature, but in the old times zinc or iron in acetic acid or
aqueous/alcoholic amalgamized aluminium were used. I can't see how aluminium with HCl could work - that would just produce a bunch of hydrogen rather
than do the reduction. On the other hand, zinc with HCl might work with acetone, provided the acid is added appropriately slowly. For zinc, it would
still be more reasonable to simply use acetic acid or NaOH(aq). Anyway, check the literature. |
That's the problem I didn't see the difference, I thought the hydrogen evolving does the thing, but I see that is incorrect(still have no idea of
mechanism). Then if the metal is reducing the ketone directly (and hydrogens come from water somehow) then the activity of the dissolving metal used
must be important , or? Also what if I add a little NiCL2 that the nickel is going to be reduced to the metal (powder) on the Al surface - will this
improve the process somehow by "turning on" also the "classical" meaning of hydrogenation with evolved H2 from Al and acid ? (sorry for irritatingly
ignorant questions, I read that thread).
[Edited on 28-9-2013 by papaya]
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sonogashira
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You could use aluminium isopropoxide. 
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papaya
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Not a joke!
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papaya
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Interesting what I was doing is - Clemmensen reduction
http://www.organic-chemistry.org/namedreactions/clemmensen-r...
This may explain why I didn't detect isopropanol with HCL/Al - (did only once - need to recheck) it must be I generated propane instead of alcohol!
(that time I lit the gas from curiosity- it burned with silent yellow flame unlike hydrogen as a note).
However I DID detect quite good amount of alcohol(by nitrite formation) with NaOH+Al method and cannot find the analog of this reduction in literature
(the name) - as for now I found this
http://nopr.niscair.res.in/bitstream/123456789/6173/1/IJCB%2045B(1)%20332-334.pdf
May it be that in basic medium it's not anymore a Clemmensen reduction but something else?
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Nicodem
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No, you were not doing a Clemmensen reduction, which requires specific conditions, not just stirring some metal with HCl(aq). For the Clemmensen
reduction to occur, either amalgamized zinc with concentrated HCl or zinc with ethereal HCl need to be used. Aluminium does not work.
| Quote: | | However I DID detect quite good amount of alcohol(by nitrite formation) with NaOH+Al method and cannot find the analog of this reduction in literature
(the name) - as for now I found this http://nopr.niscair.res.in/bitstream/123456789/6173/1/IJCB%2045B(1)%20332-334.pdf |
That's another reaction altogether. The pinacol coupling occurs when Mg, alkali metals, or some other metals, or SmI2 reduce the ketones in
a non-protic media (or at least a media deficient of proton donors). The first intermediate, the anion radical, is the same as in the dissolving metal
reduction of ketones to alcohols, but it couples before it gets reduced further.
| Quote: | | May it be that in basic medium it's not anymore a Clemmensen reduction but something else? |
Maybe you are a bit confused on how the reactions are named. The name is not necessarily connected to a reagent, reaction media and product type. It
has to do with the reaction mechanism. The name of the reaction is a reflection of the theory, not technique.
The name of the reactions you are looking for, is the dissolving metal reductions of ketones to alcohols and I posted a review just a couple of days ago. Look there for references describing the experimental.
…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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