Hexavalent - 4-6-2012 at 04:58
Can anyone suggest a method to reduce MEK to 2-butanol (sec-butanol) that avoids the use of agents like NaHB4 or LiAlH4 (although the borohydride
would probably be best here)?? Is it possible to do it with a more common compound, e.g. an iron (II) salt or oxalic acid?
[Edited on 4-6-2012 by Hexavalent]
barley81 - 4-6-2012 at 10:59
MPV reduction using aluminum isopropoxide:
http://en.wikipedia.org/wiki/Meerwein%E2%80%93Ponndorf%E2%80...
Aluminum isopropoxide is cheap to make if you have the right stuff (vacuum pump, distillation setup, Ga or HgCl2, anhydrous iPrOH). Unfortunately the
conventional prep requires mercury chloride, but a member here had success using gallium or galinstan (I forget).
Hexavalent - 4-6-2012 at 11:05
Thanks barley, I'll look into that. Is there a way to get aluminium to react directly with iPrOH, akin to potassium? I understand the difference in
reactivity between these metals, but is there a way?
I was speaking to woelen and he suggested using nascent hydrogen in situ as the reductor. What are your thoughts on this? Theoretically it should
work, but has anyone here ever tried it that way?
sargent1015 - 4-6-2012 at 11:09
Interesting, do you by chance have the work up procedure after the MPV reaction is complete?
barley81 - 4-6-2012 at 11:21
Aluminum would react with isopropyl alcohol directly if it weren't for that pesky oxide layer. Anything that breaks that layer like mercury or gallium
will help the aluminum to react.
Nascent hydrogen? With zinc amalgam, you would get butane. I heard that aluminum amalgam can reduce ketones to alcohols from several places, but I
have not seen very many examples.
http://www.sciencedirect.com/science/article/pii/S0040403900...
Hexavalent - 4-6-2012 at 11:31
Could Al foil sheets (3mm thick) not be scrubbed down iron wool prior to inserting them into IPA? What about a quick HCl wash to dissolve the Al layer
before they go in, followed by a dip in distilled water? Would it have enough time within those steps to regain its oxidative coating before being
insert into the alcohol?
Woelen suggested that adding some dilute (5-10%) HCl (aq) to the MEK followed by some zinc powder would generate nascent hydrogen that would react
nicely as a reductor and take the MEK back to 2-butanol (the secondary alcohol), akin to acetone being reduced to iPrOH.
DJF90 - 4-6-2012 at 12:03
Nascent hydrogen is a thing of old that was used to describe "dissolving metal reduction" before the chemists had any idea about the electrons doing
the reducing. Treatment of acetone with Mg/Hg in HCl will yeild pinacol, so if you're going to go this route you should probably be careful/selective
about what metals/conditions you use. Sodium metal in ethanol or methanol will certainly do the trick, although dissolution in the latter is much more
vigorous. But you certainly haven't searched very well, considering it was discussed not that long ago here! http://www.sciencemadness.org/talk/viewthread.php?tid=19841
Work up will best be effected by adding a (half) saturated solution of rochelle salt, to complex the aluminium ions and prevent formation of a nasty
emulsion! I guess diluting with ethyl acetate or something before addition of the aqueous phase would be a good idea too...
[Edited on 4-6-2012 by DJF90]
Hexavalent - 5-6-2012 at 04:47
Thanks for that DJF90, I admit I missed the thread you pointed out.
On a side note, therefore, is it viable that pinacol could be synthesised in this method, using the Mg/HCl/acetone method?
Here's a reaction - the Pinacol coupling of acetone - from Wikipedia;
and then I assume as it is a vicinal-diol, it can rearrange to pinacolone by the pinacol rearrangement, e.g. by heating with sulfuric acid?? Like;
Then hypothetically it could be reacted with borane and/or boron trichloride to produce intermediates such as pinacolborane, bis(pinacolato)diboron,
and pinacolchloroborane . . .pity the reactant gasses are so dangerous and unfeasible to use for the amateur!
[Edited on 5-6-2012 by Hexavalent]
Adas - 5-6-2012 at 06:28
Why not dissolve a bit of NaOH in the IPA to get rid of the Al2O3 layer?
Hexavalent - 5-6-2012 at 08:38
Good idea Adas.....but you'd have to be careful not to add too much lest it mess up the main reduction somehow.
Adas - 5-6-2012 at 09:42
I don't think the reduction can be messed up too much if you add little more NaOH. 
But sure, the amount needed is very small.
Hexavalent - 5-6-2012 at 10:05
Indeed, the oxide layer is probably only thin, and all that is needed is enough to go;
Al2O3 + 2 NaOH = Na2Al2O4 + H2O