fastbre4k
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Ketone to Alcohol with Mg
I have read a document that says:
9.1g Benzophenone solved in 200ccm Methylalcohol (anhyd.).
Under reflux 4.55g Magnesium tape is addet, 0.2mm thick, fresh polished and cut into 1cm pieces.
The Lively reaction was calmed with a water bath.
The metal dissolved within 2 hours and a clear solution was formed.
The Methanol was stripped and under stirring ice water was added.
With Acetic acid (80%) the Ph was adjusted to a weak low Ph.
The last pieces of Mg(OH)2 dissolved with a bit of heating And a colorless oil appears in the solution what solidifies on cooling.
That was dried under vacuum and recrystallized from Ligroin to yield 8.2g of snow white needles - yield 89% mp. 67,5°C
The Diphenylmethanol gave a red color on reaction with Sulfuric acid.
I guess Methanol can replaced by Ethanol - that would be a clean and easy procedure for making alcohols from ketones.
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JJay
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This looks pretty similar to MPV reduction with aluminum but apparently doesn't require any mercury. I suspect methanol works better than ethanol, but
from a quick search, it looks like people have performed similar reductions in ethanol as well.
I wonder if it works on aromatic or unsaturated aldehydes.
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zed
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Might be a special case. Seems to me, Ketones are not generally easily reduced to alcohols.
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byko3y
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I would be glad to read some good review on this kind of reactions. But AFAIK, there's none  . Some steroidic ketones can be reduced to alcohol by sodium methoxide in low yields.
BTW, magnesium+NH4OAc is capable of reducing some phenone-derrived oximes. I'm ready to accept the benzophenone->benzhydrol conversion, but the
1,3-diphenylacetone and acetophenone example are not that easy in reduction, I wonder if it's truly MPV reduction, which works on a wide range of
ketonic substrates.
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zed
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Well, seems to me, Ethanol can work in the MPV, and Isopropanol is better, but this doesn't look like the MPV.
In this case, it looks like we have a dissolving metal reduction. In many cases, the MPV requires no metal present, or a merely catalytic amount.
[Edited on 27-12-2016 by zed]
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CuReUS
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see this thread - http://www.sciencemadness.org/talk/viewthread.php?tid=66545 ,the pdf also gives reference for the reduction of ketones using Mg/MeOH
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byko3y
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Well, the article at https://dx.doi.org/10.1021/ja01409a042 confirms that benzophenone is indeed reduced be magnesium metal and not magnesium amalgam. Also you can
find a reduction of ring-deactivated benzyl alcohol by Mg/MeOH. Magnesium is known to form benzophenone lketyl radical. Also Mg-NH4OAc reduces
benzylic oximes, but not aliphatic ones.
Summarizing the observations: magnesium is capable of reacting with benzylic group. Still I don't understand how the 1,3-diphenylacetone is reduced.
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