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.
JJay - 26-12-2016 at 04:28
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.zed - 26-12-2016 at 19:22
Might be a special case. Seems to me, Ketones are not generally easily reduced to alcohols.byko3y - 27-12-2016 at 07:26
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.zed - 27-12-2016 at 15:24
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]CuReUS - 28-12-2016 at 04:53
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.
. Some steroidic ketones can be reduced to alcohol by sodium methoxide in low yields.