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AJKOER
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I read that methanol is much more vigorous in reacting with a Mg alloy (or Mg with a catalyst including chlorides of Hg, Cd, Pd, Co, Ni,..., which
could than form a galvanic couple, see G.H. Lee, et al, "Magnesium in Methanol (Mg/MeOH) in Organic Syntheses", published in Current Organic
Chemistry, 2004, 8, 1263-1287 1263, full text available at https://www.google.com/url?sa=t&source=web&rct=j&... , which is an SM talk file ) than ethanol.
You may be able to use this to quickly visually (as distinct from smell based methods) estimate CH3OH content by running comparative tests with a pure
methanol and a pure ethanol sample for your particular magnesium alloy source.
The reaction between Mg and methanol is said, after a possible inception period, to proceed in an exothermic manner that may require cooling. One of
the products of the reaction is Mg(CH3O)2.
Example of some possible reaction paths with a galvanic couple producing a current:
2 CH3OH + 2 e- = 2 CH3O- + H2
Or, a path leading to HCHO:
H2O + e- = .H + OH-
CH3OH + .H = .CH2OH + H2
.CH2OH + Fe(lll)/Co(lll) = HCHO + H+ + Fe(ll)/Co(ll)
Reference: See equations (1), (3) and (4) in the open article, "Dehydrogenation of anhydrous methanol at room temperature by o-aminophenol-based
photocatalysts", by Masanori Wakizaka, et al, in Nature Communications 7, Article number: 12333, (2016), doi:10.1038/ncomms12333:fc "Dehydrogenation
of anhydrous methanol at room temperature by o-aminophenol-based photocatalysts", by Masanori Wakizaka, et al, in Nature Communications 7, Article
number: 12333, (2016), doi:10.1038/ncomms12333, Link: http://www.nature.com/articles/ncomms12333
Another reference, in the possible use of magnesium metal, cites Mg turnings, pretreated with HCl and employed at 50 C, in select organic synthesis
(please see commentary at: http://pubs.acs.org/doi/abs/10.1021/jo00210a035 . Article: "Magnesium in methanol: substitute for sodium amalgam in desulfonylation reactions", by
Alan C. Brown and Louis A. Carpino, in The Journal of Organic Chemistry, Vol. 50: Issue. 10: pages. 1749-1750, 1985).
[Edited on 11-6-2017 by AJKOER]
[Edited on 11-6-2017 by AJKOER]
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draculic acid69
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I was about to start a post about this exact thing and as I googled the page I was looking for this post popped
up.https://forums.whirlpool.net.au/archive/2235624 is the best discussion on this topic so far.i would try a sodium bisulfite addition to trap ketones
and aldehydes.or a boil with hydroxides to break any esters and polymerize ketones and aldehydes. I'd also recommend a cryogenic crystallization to
freeze out any unwanted substances.in the above link the guy describes an olive oil purification that sounds like a really clever trick.
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Boffis
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We use a clear "bio-ethanol" in table warmers. It has a distinct small of MEK so today I tried a little experiment and add a few ml of 50% sodium
hydrogen sulphite solution to it. The alcohol became cloudy but that could be jst the low solubility of Na H sulphite in 95% alcohol. The label on the
can does not state what the denaturants are but distillation alone did not remove the smell of MEK. Interestingly the bisulphite solution did! I
filtered off the white precipitate, the quantity was tiny and is drying at present but when mixed with a little dilute acid it regenerates the ketone
smell plus sulphur dioxide.
The filtered alcohol was treated with calcium hydroxide to precipitate the excess SO2 as calcium sulphite. Tomorrow I'll filter and distill it.
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Pumukli
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Great! Please keep us updated on how well/unwell the process really went! I've been working with MEK denatured ethanol recently and reached a point
where this denaturant really caused problems. (No, it was not about strengthening apple cider.)
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zed
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Hnuh?
Converting methylated spirits to drinking likker?
Gosh! Sounds like a great idea.
Keep us posted!
But, buy yerself a braille-keyboard, or a voice activated computer system, and practice with it for a while, before you embark on the ultimate
drinkin' experiment.
That way, if things go squinky, you can still share your results with us.
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Pumukli
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In these parts of the globe "methylated spirits" is a misnomer, the actual product doesn't contain methanol. It is pure ethanol but made undrinkable
by addition of methyl-ethyl-ketone and/or denatonium benzoate, sometimes a dye also added.
So if one could get rid of the denaturant ketone the resulting ethanol would -in theory- become drinkable.
Getting rid of the ketone is the tricky part of course, because it forms an azeotrope with the ethanol and can't be separated easily.
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draculic acid69
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Here in Australia the metho as it's known contains no methanol either. I think it's denatonium benzoate mek, ethyl acetate and some other stuff
suspected to be cyclohexyl something or other. I think the purple stuff has a different composition to it as it smells different.but I think they can
definitely be made drinkable.
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zed
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Ah! Well, here in the USA, "Methylated" means "Methylated".
Often 20% Methanol, or higher. I recently considered purchasing some Methylated Spirits for lab use. Had so much Methanol and other weird shit in
it, that I decided it just wouldn't work out. The Methanol to Ethanol ratio, was very unfavorable.
This stuff will blind you and kill you. Might have enough Methanol present, to kill you, three times over.
Moreover, the ATF (Alcohol, Tobacco, and Firearms) is wildly enthusiastic about imprisoning folks who produce distilled ethanol products, without
paying the beverage tax.
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Assured Fish
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Zed The reason i started this thread was not to make a cheap source for ethanol for drinking purposes, the thread title might be a
tad misleading (i had assumed people would understand the hypothetical part).
Im pretty sure we all have access to methylated spirits OTC for cheap and so i just wanted to find a way to make this stuff pure enough to use for any
chemical reaction no matter how scrupulous the required conditions.
I know a few people have tried using methylated spirits ethanol in certain preps and found it to fail whereas ethanol prepared from fermentation tends
to work fine.
The issue is that we cannot all do our own ferment and sugar isn't cheap.
I think i have come to the conclusion that in reality if i needed ethanol for a very sensitive reaction i would happily just make it via fermentation
or dig into the drinking stock, then just use the methylated spirits for making ether and the likes.
But the topic still carries merit atleast for curiosity sake, I mean come on surely you haven't atleast considered how pure you could make that stuff?
Sufficiently advanced science is indistinguishable from madness.
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Pumukli
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Back to the topic: once I tried dissolving NaOH (a few percent) into the stuff and then added a few grams of kitchen Al foil pieces. The content of
the flask was stirred with a magnetic stirrer. Reaction was fairly vigorous. The addition of the foil took 1-2 hours, expect heavy bubbling, frothing,
anything.
With the help of Al foil one could remove all water and maybe reduce the MEK to sec-butanol. Sec-butanol boils around 100 C, hence the conversion
-theoretically- would give you 20-22 C difference in the boiling points. With a fractionating column it may be possible to get pure (absolute!)
ethanol from the "sludge".
The smell of the stuff after this treatment changed appreciably, maybe the reduction was successful, I don't know. I just distilled (without column)
the contents of the flask. I don't have a decent column so I did not bothered.
I think MEK can ruin the smell/taste of ethanol even at 0.02% concentration, so this method even with 99% conversion (I doubt that rate) would yield
an undrinkable spirit. But that spirit would be much better suited for chemical reactions and would be absolute (in the sense of free from water)
ethanol!
Anyway it is just something one can ponder about. 
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AJKOER
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Perhaps a different approach in the case of other organic additives that CH3OH, add Mg to create the magnesium ethoxide and hydrogen. Isolate the
solid salt free from moisture (assuming no other magnesium salts are formed).
When in need of the ethanol for an application, add water (which can react violently liberating pure ethanol and Mg(OH)2).
Note: This is immediate prep for the ethoxide and not ethanol via distillation (which may be an important legal distinction).
Obvious economic issue is the cost of the magnesium source metal.
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Pumukli
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I read somewhere that ethanol and higher alcohols are hard to convince to react with magnesium. Only methanol reacts with it relatively readily.
I've seen it myself: I could make Mg-methoxide but only after a few drops of ethylene-bromide were added to the Mg - methanol mixture to activate my
magnesium. My denatured ethanol did not react with the same Mg.
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AJKOER
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Surface area of the Mg makes a difference, and surface preparation by either pre-washing it with dilute HCl, conc NH4Cl(aq), dibromoethane, stirring
with added glass shards to expose fresh metal, or crushing magnesium turnings, ..., are among many other recommendations presented by researchers
available at:
https://www.researchgate.net/post/Does_anyone_know_the_best_...
Magnesium metal reactions with many inorganic and some organics compounds has been reported in some old publications for a specified surface area of
magnesium (see https://books.google.com/books?id=jvjmAAAAMAAJ&pg=RA1-PA... ).
The source also notes that a magnesium amalgam (created by heating Mg and Hg together) is more reactive.
[Edited on 18-6-2019 by AJKOER]
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Tsjerk
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Quote: Originally posted by Pumukli  | I read somewhere that ethanol and higher alcohols are hard to convince to react with magnesium. Only methanol reacts with it relatively readily.
I've seen it myself: I could make Mg-methoxide but only after a few drops of ethylene-bromide were added to the Mg - methanol mixture to activate my
magnesium. My denatured ethanol did not react with the same Mg. |
Have you tried this with your denatured ethanol, Mg and ethylene-bromide?
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AJKOER
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Came across a reference (see full discussion at
https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Organic_Chemistry)/Alcohols/Properties_of_Alcohols/Acidities_of_Alcoho
ls ), to quote in part:
"When considering alcohols as organic reagents, pKas are often used because they reflect reactivity in aqueous solution. In general, alcohols in
aqueous solution are slightly less acidic than water. However, the differences among the pKas of the alcohols are not large."
where the cited PKa of methanol was 15.5 versus ethanol of 15.9. And to quote further:
"There are many sites on the internet with explanations of the relative ordering of alcohol acidities in aqueous solution. The general explanation is
that the larger substituents are better electron donors, which destabilize the resulting alkoxide anions. Because hydrogen is least donating of the
substituents, water is the strongest acid. Unfortunately, although this belief persists, it is incomplete because it does not account for the
gas-phase results. The problem with the electron donation explanation is that it suggests that the order of acidity is due solely to the intrinsic
electronic effects of the substituents. However, if that were the case, the electron donating effect should also be evident in the gas-phase data.
However, the relative acidities in the gas phase are opposite to those in aqueous solution. Consequently, any interpretation of the acidities of
alcohols must take the gas phase data into account.....The inversion of the acidities of alcohols between the gas phase and aqueous solution was
pointed out by Brauman and Blair in 1968.[3] They proposed that the ordering of acidities of alcohols in solution is predominantly due to the
combination of a) polarizibility and b) solvation, and that the electron donating ability of the substituent does not play a significant role.[4]"
The above comments should be taken into consideration in any suggested chemical base separation path between methanol and ethanol.
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Tsjerk
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The difference in pKa is only relevant for reactions without a catalyst, at least for determining whether or not the reaction will proceed.
Also reactions running at reflux will not care too much about a pKa difference of 0.4, as the speed of the reaction will be mostly compensated by the
higher temperature.
I don't know of a reaction that does not run with either ethanol or methanol, but that does with the other, where no catalyst is present. But I'm
happy to be corrected.
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Pumukli
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No, I did not try the rxn with ethylenebromide. I simply didn't want to contaminate the ethanol with some unreacted carcinogene. (We are talking about
hypothetically drinkable ethanol, right? Using a carcinogene would defeat the purpose of the whole procedure. Even if we don't want to drink that
ethanol in the end.)
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Tsjerk
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The reason I asked is because you're claiming a difference in reactivity between methanol and ethanol, and then use an example were you use a catalyst
and compare this with a reaction without a catalyst... A little bit like comparing apples with pears.
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