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Actually I am somewhat wrong after looking into it more. It does form the imine, but it's not part of the reduction, it forms first via the pathway
Joseph mentioned. Then it is actually the imine that is reduced to form the carbonyl-amine condensation product, so the ketone itself should never
actually be reduced.
Knowing that it would have likely been better to combine the ammonia and acetone first before adding the HgCl2, but at the time I did not know how
vigorously it would react so I wouldn't have done it differently. As discussed there may not have been much imine formation without the aluminum to
push it to the right though.
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Melgar
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You still seem to be confused as far as terminology. The imine is not reduced to form a carbonyl-amine condensation product, the imine IS a
carbonyl-amine condensation product. And imine formation is not a redox reaction, since both before and after, the carbon is double-bonded to a more
electronegative atom.
I'm concerned about your use of mercury just for screwing around, though. I would personally never use lead or mercury for any reaction that I wasn't
already 99% sure of what the products would be. There are safer alternatives. Are you in the US? If so, I'll mail you some of this aluminum/gallium
alloy stuff I've been experimenting with, for free. It'll reduce all the same things, at least it should. And if there are differences, they're
differences that haven't been documented yet, so you'd be breaking new ground, scientifically. The only other research I'm aware of on this alloy is
by a team at Purdue, that's only using it to generate hydrogen from aluminum.
If you save the wastes, you can reclaim gallium and whatever metals are more electropositive from it, then use the salts like you would mercury salts
for a reduction. There are differences in procedure, but not not many. The last thing you need is to get lax with safety and accidentally discover a
new synthesis for dimethylmercury or something.
The first step in the process of learning something is admitting that you don't know it already.
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| Quote: | | You still seem to be confused as far as terminology. The imine is not reduced to form a carbonyl-amine condensation product, the imine IS a
carbonyl-amine condensation product. And imine formation is not a redox reaction, since both before and after, the carbon is double-bonded to a more
electronegative atom. |
You're right. I did realize that and understand the mechanism/pathway now, but I did still use the wrong termonology in that sense. I did not mean
that the reduction itself creates the condensation product just that after the reduction you have your target, reduced, condensation product.
| Quote: |
I'm concerned about your use of mercury just for screwing around, though. I would personally never use lead or mercury for any reaction that I wasn't
already 99% sure of what the products would be. There are safer alternatives. Are you in the US? If so, I'll mail you some of this aluminum/gallium
alloy stuff I've been experimenting with, for free. It'll reduce all the same things, at least it should. And if there are differences, they're
differences that haven't been documented yet, so you'd be breaking new ground, scientifically. The only other research I'm aware of on this alloy is
by a team at Purdue, that's only using it to generate hydrogen from aluminum.
If you save the wastes, you can reclaim gallium and whatever metals are more electropositive from it, then use the salts like you would mercury salts
for a reduction. There are differences in procedure, but not not many. The last thing you need is to get lax with safety and accidentally discover a
new synthesis for dimethylmercury or something. |
That's very kind. I am in the US so if you are offering I'll take you up on it, I was considering that some time back but did not pursue it.
I am relatively safe with the mercury, and I don't dump it down the drain or anything like that, but I'd definitely prefer not to work with it if
possible. There are some alternatives that I have available, CuSO4/A and, Zinc/HCl come to mind, but I actually went with the Hg/Al because I
was not sure if it would work.
Maybe that logic is backwards, but my thought was that if it doesn't reduce with Hg/Al, the most effective reducing agent I have, then it's reasonable
to conclude a reduction is not viable. Yet if I tried with say CuSO4/Al and it did not work then all I can conclude is CuSO4 did not work but Hg/Al
still may.
edit: Still grappling with the quote tags...
[Edited on 13-6-2017 by alking]
edit2: Actually I noticed you said above that you can 'use the [gallium] salts like you would Hg.' Are you saying that from experience or just
theoretically? When I was researching Ga before the consensus seemed to be that you had to alloy it and creating an HCl or something is not very
effective as it's hard to dissolve and I couldn't find any reports of someone actually using it that way.
[Edited on 13-6-2017 by alking]
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Corrosive Joeseph
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Quote: Originally posted by Melgar  | Imine formation is reversible. Typically, the reaction is driven in a particular direction by either adding or removing water. If you want the imine
to preferentially form, you need to remove water. Since aluminum amalgam reacts with water, that's usually how it's done.
|
Thank you for that quality piece of information, I didn't know that. I was wrong myself in thinking it wouldn't go well in water.
And this thread has interested me enough to look at this even closer..........
"The Al/Hg reduction system definitivly needs water, no water or not enough water - no reaction. It is mostly almost not possible to use to much
water, for reductive aminations often 40% methylamine in WATER is used with excellent results." - Organikum
and from the same thread...........
"Anyway, the dissolving aluminium does not give a fuck about whether the proton donor is water, methanol, acetic acid or whatever else. The pKa of the
proton donor will however influence the overvoltage at the metal surface. So, too acidic proton donors (like HCl, etc.) are no good since too much
metal gets consumed by the reduction of H(+) to H2 and not enough acidic proton donors will slow down the reduction to a useless pace. Solvents like
MeOH, H2O and conditionally AcOH are just OK for the dissolving metal reductions with aluminium amalgam. All there is to do is to adjust the solvent
or combination of solvents to the substrate that is to be reduced." - Nicodem
"waterless al/hg?" - https://www.sciencemadness.org/talk/viewthread.php?tid=8452
also...........
"Pressurerized Al/Hg as on Rhodiums page but with ammomia in ethanol (94% alc. is ok). Yield: 50% to 60%
Add the amine in alcohol to the ketone and let sit for some hours. This should warm up on addition. Then do the Al/Hg under pressure (3 to 5 atm is
ok).
Ratios amine to ketone 1 to 1,5 molar." - Organikum
" Reduction of carbonyl groups" - https://www.sciencemadness.org/talk/viewthread.php?tid=627
Never mind the pressure thing, Orgy seemed to like that one, just posting an example of forming the imine first for the OP...........
/CJ
[Edited on 13-6-2017 by Corrosive Joeseph]
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Melgar
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| Quote: Originally posted by alking | | Quote: |
I'm concerned about your use of mercury just for screwing around, though. I would personally never use lead or mercury for any reaction that I wasn't
already 99% sure of what the products would be. There are safer alternatives. Are you in the US? If so, I'll mail you some of this aluminum/gallium
alloy stuff I've been experimenting with, for free. It'll reduce all the same things, at least it should. And if there are differences, they're
differences that haven't been documented yet, so you'd be breaking new ground, scientifically. The only other research I'm aware of on this alloy is
by a team at Purdue, that's only using it to generate hydrogen from aluminum.
If you save the wastes, you can reclaim gallium and whatever metals are more electropositive from it, then use the salts like you would mercury salts
for a reduction. There are differences in procedure, but not not many. The last thing you need is to get lax with safety and accidentally discover a
new synthesis for dimethylmercury or something. |
That's very kind. I am in the US so if you are offering I'll take you up on it, I was considering that some time back but did not pursue it.
|
U2U me your address, and I'll get it out in the mail. Just promise not to use mercury salts "just to see what happens", and only when you know
exactly what you're doing, ok? This gallium alloy you can eat on your corn flakes and be fine, so use it for anything you can think of.
| Quote: | I am relatively safe with the mercury, and I don't dump it down the drain or anything like that, but I'd definitely prefer not to work with it if
possible. There are some alternatives that I have available, CuSO4/A and, Zinc/HCl come to mind, but I actually went with the Hg/Al because I
was not sure if it would work.
Maybe that logic is backwards, but my thought was that if it doesn't reduce with Hg/Al, the most effective reducing agent I have, then it's reasonable
to conclude a reduction is not viable. Yet if I tried with say CuSO4/Al and it did not work then all I can conclude is CuSO4 did not work but Hg/Al
still may. |
Well, in that case, the logic is wrong rather than backwards. Reducing agents aren't on a linear scale from strongest to weakest. I mean, there are
stronger ones and weaker ones, but they all have their preferred functional groups for reducing. Sodium borohydride, for example, prefers to reduce
ketones and aldehydes to alcohols, but will perform other reductions too, given enough time. All the PGMs have their own preferences too.
[Edited on 13-6-2017 by alking]
| Quote: | | edit2: Actually I noticed you said above that you can 'use the [gallium] salts like you would Hg.' Are you saying that from experience or just
theoretically? When I was researching Ga before the consensus seemed to be that you had to alloy it and creating an HCl or something is not very
effective as it's hard to dissolve and I couldn't find any reports of someone actually using it that way. |
Original research that I haven't written up yet. Gallium dissolves just fine in HCl + H2O2, and will actually do its "angry dance" if conditions are
just right and temperature rises to near the H2O2 decomposition temperature. That's where it's a melted ball, and bubbles are forming so quickly on
its surface that it bounces all over the inside of the liquid in the flask. The trick is that you have to add gallium at a temperature well above its
melting point, so like 50˚C.. This allows it to be reduced in localized spots on the aluminum, since reduction takes place much more quickly in
areas where there's liquid gallium present. Otherwise, it deposits in scattered areas all over the surface, and doesn't form those localized liquid
areas like mercury does. Once gallium is deposited, and you can see some bubbling, let it cool down before adding the indium chloride. You'll
understand why I said to do that when you see the rapid increase in reactivity. Add indium chloride solution slowly, in any case, because you're sort
of tuning the reaction at this point. Tin seems to be helpful as a catalyst, but it's hard to say for sure. I usually use the alloy containing all
the different metals myself.
For rquote blocks, which are automatically added to your response, you need to end in a /rquote end tag. A
quote bloc, on the other hand, has to always end with a /quote.
| Quote: | I didn't know that. I was wrong myself in thinking it wouldn't go well in water.
And this thread has interested me enough to look at this even closer.......... |
Actually, you were right about how it would perform in water. Water needs to be removed from the reaction since it's a product of imine formation.
Removing the formed water prevents the reaction from going backwards./
[Edited on 6/14/17 by Melgar]
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Melgar
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In my experience, the reason for the water is to react with the aluminum alkoxides to precipitate out the aluminum oxides. Aluminum alkoxides are
gel-like and not very soluble in the alcohol, so they tend to coat the aluminum's surface. Water reacts with the alkoxides to give back the alcohol
and a much denser, powdery aluminum oxide.
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Corrosive Joeseph
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@ Meglar - Could you elaborate on that, I always thought it was aluminium hydroxide that was one of the end products..........?
"The presence of water in the solution is reportedly helpful—even necessary; the electron rich amalgam will oxidize aluminium and reduce H+ from
water, creating aluminium hydroxide (Al(OH)3) and hydrogen gas (H2). The electrons from the aluminium reduce mercuric Hg2+ ion to metallic mercury.
The metallic mercury can then form an amalgam with the exposed aluminium metal. The amalgamated aluminium then is oxidized by water, converting the
aluminium to aluminium hydroxide and releasing free metallic mercury. The generated mercury then cycles through these last two steps until the
aluminium metal supply is exhausted.[4]
The three reaction steps of the aluminium amalgam reaction. The first step reduces mercury ions to mercury metal. While the bottom two reactions
continuously cycle until the aluminium supply is exhausted.
2 Al + 3 Hg2+ + 6 H20 --> 2 Al(OH)3 + 6H+ + 2Hg
Hg + Al --> Hg-Al
2Hg-Al + 6 H2O --> 2 Al(OH)3 + 2Hg + 3 H2"
Taken from - https://en.wikipedia.org/wiki/Aluminium_amalgam (Please excuse my terrible subscript and superscript technique, there isn't any)
And from this thread - "Aluminium amalgam" - http://www.sciencemadness.org/talk/viewthread.php?tid=20625
"And just a short note: if pure chemicals are used (abs. propanol) then no Al2O3 should form during this reaction."
I presume this means no water............?
and from the same thread -
"To see the stuff in your Al foil, soak it for about an hour in vinegar (we are trying to remove a plastic coating). Rinse and place in a container of
aqueous ammonia. You will see tiny bubbles as the protective Al2O3 layer is circumvented by the rise in pH and the Al reacts with water forming H2 and
a clear gelatinous Al(OH)3 (saturated with aqueous ammonia). In about a day or two, all that will remain is a black residue (Carbon or Silicon I
suspect). "
The more I know, the more I realize I don't know (facepalm)
/CJ
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Melgar
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Aluminum hydroxide <-> aluminum oxide is also reversible. (2 Al(OH)3 <-> Al2O3 + 3 H2O) In an aqueous solution, hydroxide will dominate,
but if not, the oxide will. This is convenient, since the oxide is denser and doesn't form a sludge. This is one of the reasons to avoid a
mostly-aqueous solution. Additionally, like iron, aluminum can have mixed oxide-hydroxide compounds, which are virtually always found in products of
aluminum reduction. In this case, it doesn't matter if it forms Al2O3, because by that point it's already in solution and not adhered to the aluminum
surface.
Also, the one poster was right about Al2O3 not forming if the alcohol was pure. This is because it all becomes aluminum isopropoxide, and water is
needed to turn that into the hydroxy compound, which would then be dehydrated to Al2O3, presumably due to the low water content.
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Corrosive Joeseph
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Oh-kay............. The whole reaction is very complex actually.......... I'm still trying to get my head round it but I can see it more clearly
now........... Sheesh
I looked at this a while ago, in the hope of preparing primary amines from OTC ketones, but I never really saw anything very concrete.
Short chain aliphatic ketones (acetone and MEK) just don't seem to do well in any reductive amination from what I have read.
Here is another one -
"Most of the yields reported in preparations of primary amines from simple aliphatic ketones are better than 50%. The
yields from acetone and methyl ethyl ketone, in preparations carried out with hydrogen and a nickel catalyst, are only about 30%.
However, methyl n-propyl ketone 12 and methyl isopropyl ketonex are converted to the primary amines in yields of 90% and 65%, respectively.
The yield of cyclohexylamine from cyclohexanone is about 80%."
I read 30% EVERY time, with EVERY method.
That was taken from 'The Preparation of Amines by Reductive Alkylation' in 'Organic Reactions Vol. 4',
It is in the SM library - http://library.sciencemadness.org/library/books/organic_reac... -
Much great information in that chapter, but all reduction methods are hydrogenation and metal catalyst (usually Ni)
Modern researchers seem to prefer NaBH3CN............ Pfft..........!!
Al-Hg on cyclohexanone to cyclohexamine looks much more promising.
Does anyone have any experience with this or know of any reports..........?
In the middle of all my digging, I found this -
" The Al/Hg gives 85% and more and workup is not bad if done right and no unnecessary excess of Al was used (in cases the product steamdistills workup
is cake anyways)."
[EDIT] - Just realized this is with alkylamine and not ammonia........ Grrrr
Taken from - "wet aminative reduction" - http://www.sciencemadness.org/talk/viewthread.php?tid=19587
Anyways, out of useful information for now. Where's my shovel...........
/CJ
Attached - Reductive Amination of Aldehydes and Ketones - Mechanics and Selectivity
Attachment: Reductive Amination of Aldehydes and Ketones - Mechanics and Selectivity.pdf (256kB)
This file has been downloaded 485 times
[Edited on 19-6-2017 by Corrosive Joeseph]
[Edited on 19-6-2017 by Corrosive Joeseph]
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Corrosive Joeseph
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Please excuse the double post...........
For the OP - Taken from the attachment above -
"The initially formed primary amines can, in their turn, behave as aminating agents for carbonyl compounds to afford secondary
amines.
It was proposed as well that primary amines react with imines, forming an addition product, which can directly be reduced to the secondary amine. The
secondary amine would react similarly with either the carbonyl compound or the imine to give the tertiary amine through hydrogenation of the
corresponding carbinolamine or gem-diamine intermediate (Scheme 2).[7]
However, a kinetic study on the reductive amination of acetone with NH3 revealed that both isopropylamine and diisopropylamine are obtained through
hydrogenation of the imine intermediates formed from acetone and NH3 or acetone and isopropylamine, respectively.
A separate study of the reaction of acetone and isopropylamine showed that the diisopropylimine equilibration reaction is acid catalysed (Scheme
3).[8]"
Still found no report of a Leuckart on acetone, except a post from Leu -
"You will need a pressure vessel to carry out a leuckart reaction using formamide with acetone, as acetone is a vapor at the temperatures that a
Leuckart reaction occurs at atmospheric pressure  One might be able to use an
alternative such as CTH or catalytic hydrogenation, but LAH is what was used in the published papers  "
https://www.sciencemadness.org/whisper/viewthread.php?tid=56...
Hmmm.......... Makes sense I guess
There is an excellent chapter on the Leuckart in Organic Reactions 5 - http://library.sciencemadness.org/library/books/organic_reac...
The only mention of acetone is -
Acetone + a-Naphtylamine + Methyl Formate ---> N-Isopropyl-a-naphthylamine
No stated yield........ Only a Ref #
And no mention of MEK.
Over and out
/CJ
[EDIT] - Still looking for a reported Al-Hg on cyclohexanone and ammonia...... Nothing yet
[Edited on 21-6-2017 by Corrosive Joeseph]
[Edited on 21-6-2017 by Corrosive Joeseph]
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Melgar
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Pressure reactions are easy to do at a small scale. Little one-ounce glass bottles can hold at least 100 psi if they have a good enough lid. Ive
reacted fairly substantial quantities of aluminum with iodine in 10-mL bottles, and despite the purple and brown storm going on inside, it held. The
smaller the vessel, the higher pressures it's capable of, typically.
Most cyclohexylamine is produced by hydrogenating the ring on aniline (which is formed by perhaps the easiest reduction in organic chemistry from
nitrobenzene). You can probably do this with the room-temperature Birch reduction variant that uses amines rather than ammonia. Or a regular Birch
reduction, if you have that capability.
If you're only trying to make it because a certain Dr. Shulgin was fond of using it, you can use pretty much any high-boiling primary amine that's
relatively stable. Decarboxylate phenylalanine to get phenethylamine, for instance.
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Corrosive Joeseph
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Thanks Melgar, that was all I had dug up so far....... Most of it posted for the OP and the benefit of the others in the future
I found MANY routes to Cyclohexylamine but nearly all of them are out of my reach.
Cyclohexanone is OTC at the local auto parts store/motor factors and mercury and aluminum foil are cheap......!!
I just thought it interesting. And nobody seems to have done it.
Every other reductive amination method I found yielded around 70% on Cyclohexanone.
Much better than acetone or MEK, that's for sure......
Regarding Sasha, he was most fond of using ammonium acetate, which, by all accounts, is a woeful Knoevenagel catalyst.
The man was a genius but he didn't half use some unorthodox methods.
I just want low MW amines, not the crazy ones he was making.......!!
Thanks for the heads up on the PEA
/CJ
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Melgar
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I think he only used cyclohexylamine because of how cheap it is to purchase for chemists, industrially. It's a precursor to one of the most common
artificial sweeteners used in Europe, cyclamate, and it's easily made from aniline, which is bought and sold by the train-car. In bulk, it costs
about the same as isopropanol or acetone. When I realized how cheap it was as an industrial chemical, I realized it was probably one of his
throw-away chemicals, and his choice to use it was probably similar to the choice you or I might make of what to use to rinse an oily organic residue
out of some glassware.
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alking
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What is cyclohexamine sold as in autoparts stores? That's one I'd like to add to my list.
Cyclohexylamine is cheap but so are other more effective amines and the products shulgin was losing to a reduced yield were not cheap.
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Melgar
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Are you sure you're not thinking of cyclohexane or cyclohexene? "Cyclohexamine" isn't a real chemical.
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Corrosive Joeseph
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Check my post again, it is Cyclohexanone that is sold as a specialist thinners here...........
Anyways, I decided to look into this again. I am fascinated by the fact that one reaction needs water removed and the other reaction needs water to
happen.
This is before one considers the many other competing reactions going on at the same time. Anyways, more research - Taken from 'Ketones and Aldehydes'
attached below......
"Formation of Imines (Condensation Reactions)
Under appropriate conditions, primary amines (and ammonia) react with ketones or aldehydes to generate imines.
An imine is a nitrogen analogue of a ketone (or aldehyde) with a C=N nitrogen double bond instead of a C=O.
Just as amines are nucleophilic and basic, so are imines.
(Sometimes substituted imines are referred to as Schiff's bases).
Imine formation is an example of a condensation reaction -
where two molecules join together accompanied by the expulsion of a small molecule (usually water).
The mechanism of imine formation starts with the addition of the amine to the carbonyl group.
Protonation of the oxyanion and deprotonation of the nitrogen cation generates an unstable intermediate called a
carbinolamine.
The carbinolamine has its oxygen protonated, and then water acts as the good leaving group.
This acid catalyzed dehydration creates the double bond, and the last step is the removal of the proton to produce
the neutral amine product.
The pH of the reaction mixture is crucial to successful formation of imines.
The pH must be acidic to promote the dehydration step, yet if the mixture is too acidic,
then the reacting amine will be protonated, and therefore un-nucleophilic, and this would inhibit the first step.
The rate of reaction varies with the pH as follows:
[See graph in attachment 'Ketones and Aldehydes]
The best pH for imine formation is around 4.5."
and from the same document -
"Under acidic conditions, weaker nucleophiles such as water and alcohols can add.
The carbonyl group is a weak base, and in acidic solution it can become protonated.
This makes the carbon very electrophilic (see resonance structures), and so it will react with poor nucleophiles.
E.g. the acid catalyzed nucleophilic addition of water to acetone to produce the acetone hydrate.
Summary
The base catalyzed addition reactions to carbonyl compounds result from initial attack of a strong nucleophile, whereas the acid catalyzed reactions
begin with the protonation of the oxygen, followed by attack of the weaker nucleophile."
Oh dear, I presume just like acetone and NH3 (mentioned above), the mechanism for di-imine formation is also acid catalyzed.........
I also found that Cyclohexanone to Cyclohexanol reduction with Al-Hg in THF:H20 (9:1) yields 95%, and seems to be VERY favourable.
See 'Selective Cycloalkanone Reductions using Aluminum Amalgam' attached.
But when the same reaction is done in DCM, it yields 55% of a Pinacol coupling product (From 'Reductions in Organic Chemistry' by Hudlicky Pg. 118)
Okay, the big question............. If one was to attempt this should the imine be formed first and dripped on the amalgam, or should the
Cyclohexanone be dripped in the soup and the imine reduced as it is formed.........?
I was always under the impression that acidic Al-Hg prevents dimerization (this is a double bond after all)
Has anyone any advice............? There is a lot going on here.........
/CJ
Attachment: Ketones and Aldehydes.pdf (2.5MB)
This file has been downloaded 522 times
Attachment: Selective Cyclohexanone Reductions using Aluminum Amalgam.pdf (221kB)
This file has been downloaded 445 times
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Melgar
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| Quote: Originally posted by Corrosive Joeseph | | Anyways, I decided to look into this again. I am fascinated by the fact that one reaction needs water removed and the other reaction needs water to
happen. |
There are quite a lot of reactions like that, especially reactions that say they need strict anhydrous conditions, but actually need very slight
quantities of water to initiate. Far too small for that to ever be a concern for a chemist, but interesting nonetheless.
In this case, it's actually one of the reasons that this reaction is used though; since one of the reactions' products feeds into the other, and vice
versa, this keeps the reaction controlled intrinsically. For some reason, the nearest parallel I can think of is the fact that internal parasites
virtually always require two host species. The reason for this is that parasites are stupid, and would (and often do) kill their hosts if their
population got out of control within an individual. By needing two species as hosts within their life cycle, their populations are intrinsically
limited by the interaction between the species, and both species' populations. It's sort of the same with two reactions that feed into each other.
Sort of a yin-yang type of thing going on.
| Quote: | Okay, the big question............. If one was to attempt this should the imine be formed first and dripped on the amalgam, or should the
Cyclohexanone be dripped in the soup and the imine reduced as it is formed.........?
I was always under the impression that acidic Al-Hg prevents dimerization (this is a double bond after all)
Has anyone any advice............? There is a lot going on here.........
/CJ |
Neither! Do you know WHY dimerization occurs? Because of how readily primary amines undergo reductive amination! Considerably better than ammonia,
for sure. That's actually the primary use of reductive amination; to make a secondary amine from a primary amine and an aldehyde or ketone. When
making a primary amine, hydroxylamine will actually be used rather than ammonia, because of how much EASIER it is to REDUCE the resulting OXIME.
You'll notice that the three words I've capitalized are not often seen in the same sentence... (Sorry for channelling Dr. Cox from Scrubs there for a
minute.)
The same problem that you get if you try to monoalkylate primary amines with alkyl halides, will get you if you try to monoalkylate ammonia with
reductive amination and an aldehyde or ketone. If you're hell-bent on reductive amination rather than a Leuckart reaction or something, you could
possibly form the imine under anhydrous conditions, isolate it, and then reduce it, but of course, that precludes the use of Al/Hg, which for some
reason, everyone is a huge fan of except me.
[Edited on 6/28/17 by Melgar]
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Melgar
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Oh, for anyone needing cyclohexylamine, I assume you've already decided against just buying it.
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