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stoichiometric_steve
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The CTH Writeup by Barium as Tried Out by Bandil. Sciencemadness Members Clear Things Up!
see further below.
the original protocol is flawed and will only yield anything useful if correct purification of intermediates is performed.
[Edited on 28-8-2007 by stoichiometric_steve]
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Sauron
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Care to advance any explanation for this deception by bandit snd/or barium?
Any other clunkers in writeups by him/them?
I am sorry to see peer pressure forcing you to backpeddle on your criticism.
If this procedure in the hive is not reproducible then it deserves opprobrium. This forum, and that one are not formal peer reviewed venues, we are
not constrained to cautious courtesy. Call a spade a spade.
The two most likely explanations for failure to be reproducible are
: Technical flaws in the procedure
2. Poor writeup
of course, this could be a case of 3. BOTH
[Edited on 7-8-2007 by Sauron]
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stoichiometric_steve
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| Quote: | Originally posted by Sauron
Care to advance any explanation for this deception by bandit?
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what do you mean? other than collecting credit at the former hive, there is no explanation. 'tis not the first time though that a (wannabe) chemist
posts a faulted procedure, this also happens in the primary literature.
its not that i hadnt tried to make this work for like 5 times...there just never was anything near a homogenous system.
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IPN
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Would vigorous stirring be of any help?
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Nicodem
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Damn I hate people referring to some "writeups" without providing a link or citation. How the hell anybody is supposed to check what is wrong and even
what is it talked about?
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volfrahm
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Oh my
| Quote: | Originally posted by stoichiometric_steve
the writeup at the hive by bandil using Pd/C, KCOOH in IPA is, by any and all means, fake. |
I'm not doing
much with hydrogenation at the moment, and have never attempted any CTHs, but this thread caught my eye.
First, I had some trouble finding the writeup you indicated. Finally searching for the combination of reagents you mentioned, I found Post 382254 ("A
great CTH method", Novel Discourse). This was written by Barium. Bandil's name was mentioned in the thread, but it is in no way his
work. This is procedurally irrelevant, but your emphasis of the word faked intimately connected with the author makes this more a comment on
the circumstances of the writing/posting than a critique of the procedure, wouldn't you agree?
| Quote: | | there is no way of getting a solution of 250mmol partially hydrated or aqueous KCOOH in IPA, all you get is two layers. |
This is true...
| Quote: | | since this interferes with the reduction itself by not letting the substrate/catalyst/hydrogen make contact at the same time, this protocol is deemed
to fail. |
But this explanation is lacking. Your catalyst is a metal supported on a large amount of carbon; is
this ever going to be anything but a suspension? As IPN mentioned, vigorous stirring is essential to this kind of reaction. Barium states this in the
writeup, as well as his similar procedure in Beaker's "2C-B synthesis without LAH." In the absence of detail one might assume you followed this
direction, but your comments about lack of contact suggest a static reaction mix. Are you getting two layers during the reaction itself, or upon first
mixing? Because vigorous stirring probably won't allow two defined layers.
In fact, the procedure is designed to be non-homogeneous. Barium based this on US Patent 4,792,625, from which I quote:
| Quote: | This three-phase system consists of an aqueous formate salt solution, an organic, substantially water-immiscible, solution containing the substrate
which is to be reduced and a third solid phase of a Group VIII metal supported catalyst, without the need of using a solvent, high temperatures or a
phase transfer catalyst.
[...]
A major advantage of the heterogeneous catalyst systems over the homogeneous ones lies in the ease with which the catalyst can be separated after
reaction by simple filtration and reused afterwards. |
If you had trouble and you think that the solvent
system is the cause, Barium mentions that you can freely substitute EtOH and MeOH. Did you vary this in any of your 5 trials?
| Quote: | | the only valid protocol would use NH4COOH, which is soluble in MeOH. |
Ammonium is apparently the most common
formate salt used, but by no means the only one possible. And methanol is not the only usable solvent. Here's some reading if you're interested in the
theory (1,2)
| Quote: | | what do you mean? other than collecting credit at the former hive, there is no explanation. 'tis not the first time though that a (wannabe) chemist
posts a faulted procedure, this also happens in the primary literature. |
I imagine that Sauron asked because
of the way you phrased all this.
Forum researchers can easily be wrong (especially those who dose themselves with reaction products  ). Peer-reviewed research chemists can be wrong. Patent chemists can be wrong, and even prone to mislead.
This procedure was written by a respected researcher, uprated to "excellent," and praised by several very intelligent members. Its basis in literature
was clearly documented.
By employing "fake," "by any and all means fake," "wannabe chemists" you imply deceit—an intention to create something not genuine—and ineptitude.
If you insist upon such incendiary language, you should probably: a) make sure you are right, b) familiarize yourself with the theory of the reaction
to make sure your polemic makes sense, c) provide details of your process, if only to confirm that you followed it correctly, and d) try at least to
provide accurate documentation (get the author right).
Or just try to use words like "incorrect" instead of "fake." And don't insult established members of the community, even if they make a procedural
error.
Don't get me wrong, this procedure might not work after all. But based on your errors, absence of detail and lack of research into this reaction I'm
going to assume that you don't know enough to say with so much certainty that the fault is with the procedure, and not your execution of it.
If you asked a question, someone with more knowledge might be able to help you out.....
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volfrahm
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The "writeup" in question
I still have this open, so I might as well. I'm not aware of any good hive mirrors, so I'll just clutter up the board with a copy:
-----------------------------------------------------
Barium (Hive Bee)
11-22-02 08:00
No 382254
A great CTH method
(Rated as: excellent)
Ammonium formate/Pd-C is the most commonly used CTH-system I´ve seen. It has been used to reduce -NO2 -- NH2, =NOH -- NH2 to name a few types of
reductions. In the literature the reduction of aromatic nitro groups are far more common than reduction of alphatic nitro groups. This bad for us,
since we have more often a far greater interest in reducing aliphatic nitro groups. The ammoium formate/Pd-C system is awesome for aromatics but can
be very troublesome for aliphatics.
I´ve over the years had some success with the ammonium formate/Pd-C system for alipahtic nitro groups, in some cases with great yields. But far more
often terrible yields. This is even though I´ve used 10 mols formate/mol nitro. mad So cursing like mad, I´ve usually ended up using excess Red-Al
instead of dirt cheap formate CTH. frown
In the literature it´s stated that the different formate salts behave very different as hydrogen donors. Formic acid is usually the poorest donor,
sodium formate is better , then ammonium formate (and trialkylammonium formates) and finally the best donor is potassium formate. In
Patent US4792625 potassium formate is used in a CTH procees for various aromatic nitro compounds. I tried this method to make some 2C-H in Post 326004
(Barium: "Better yields", Novel Discourse) with decent yields (64%). For some reason I completely forgot all about this system until two days ago.
This method was now tried with a few nitroalkanes to see how useful it was as a overall CTH method for aliphatic nitro groups.
General method
50 mmol nitroalkane
250 mmol potassium formate
750 mmol water
25-50 ml IPA (depending on how much is needed to get a nice solution)
10%w/w 5%Pd/C (catalyst to substrate)
Add the catalyst to the reaction flask and and wet it with the water. Then add the nitroalkane dissolved in IPA and finally the formate. With good
stirring, heat the reaction mixture to about 70°C on a water bath for 1-3 hours. The reaction is over when gas evolution ceases.
Here comes a nice twist.
when the reaction is over one can carefully acidify the solution to pH 2-3, filter off the catalyst and perform the workup as usual.
Or, filter off the catalyst/KHCO3 and wash it with IPA. Dry the IPA solution with MgSO4 and distill off the IPA to get the crude amine. Save the
filter cake, because when the next batch of the same amine is to be made just dissolve the nitroalkane in IPA, add the filter cake and finally 250
mmol formic acid. Voila, potassium formate regenerated.
Do I need to mention that formic acid is dirt cheap?!
2-Nitro-1-(2,4,5-trimethoxyphenyl)-propane -- TMA-2*HCl 89%
2-Nitro-1-(3,4-ethylenedioxyphenyl)-propane -- EDA*HCl 84%
2-Nitro-1-(2-fluorophenyl)-propane -- 2-FA*HCl 85%
2-Nitro-1-(2,4,5-trimethoxyphenyl)-ethane -- 2,4,5-TMPEA*HCl 85%
2-Nitro-1-(2,4-dimethoxyphenyl)-ethane -- 2,4-DMPEA*HCl 91%
2-Nitro-1-(2,5-dimethoxyphenyl)-ethane -- 2C-H*HCl 89%
-----------------------------------------------------
EDIT: Wasn't thinking, might as well attach a copy of the thread, too. Barium writes a couple more procedural/experimental posts.
[Edited on 2007-6-8 by volfrahm]
Attachment: 000382254.html (108kB)
This file has been downloaded 1075 times
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stoichiometric_steve
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phew, wow! spiked up quite some interest there.
those 5 times i have performed the protocol originally posted by Barium (i seem to have gotten this wrong, but i only have a copy of
the thread where bandil applies this protocol to 1-(4-fluorophenyl)-2-nitropropane),
the procedure was in all casesfollowed exactly, to the point of where it was getting pretty anal.
to clear things up with volfrahm:
there was one trial with MeOH, one with EtOH and three with IPA. in all trials the mix was of course violently stirred, since it was obvious that a
static three phase system wouldnt do any good.
whats more, and this is the major cause for my ranting, there is this disturbing statement by bandil "...depending on how much [IPA] is needed to make
a nice solution", which refers to formate+substrate IN IPA.
i have attached the thread for your reference.
Attachment: cth tried by bandil.htm (47kB)
This file has been downloaded 1115 times
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volfrahm
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Ah. Details are good! 
| Quote: | Originally posted by stoichiometric_steve
there is this disturbing statement by bandil "...depending on how much [IPA] is needed to make a nice solution", which refers to formate+substrate IN
IPA. |
I'm not sure if that interpretation is accurate. Looking at the patent, the nitroalkane is dissolved in a fixed amount of alcohol as the first step,
then Pd/C, and finally formate. Barium switches the order of the first two: "Then add the nitroalkane dissolved in IPA [to the wetted Pd/C] and
finally the formate." Bandil says only: "The potassiumformate mixture was poured into the nitro/IPA flask in one portion." Less clear with the third
iteration, but all three create a solution of nitro/IPA which is then added as a unit to the other reagents. Adjustment of the viscosity of the total
suspension would (I hope) entail another step. In the absence of an object of that adjustment, and in light of the original procedure, it seems best
to assume the word "solution" is used correctly.
Bandil's writeups are good, but he often cuts some pretty big corners. There is no purification of intermediates, and reagents are generated in situ
right on top of them. We all do things differently, but there are lots of things I wouldn't attempt until I completed a synth as written; those are
two pretty big ones. Of course, Bandil supposedly got very good results with the procedure as he wrote it—but if you can't duplicate it, there's a
strong possibility of omission or error in his casual algorithm.
If you haven't yet, check out that patent. It jumps straight from theory into examples, without a lot of "claims" that usually explain the variables
in more detail. But there are several things one could play with: addition of extra catalyst after stalled conversion, and a preferred temperature
ranging 50º+ above Barium's figure, are two that leap to mind. Barium also made some modifications over the course of his three trials that are worth
thinking about; acetic acid isn't mentioned in all of the trials.
Maybe ignore Bandil's synthetic bridging and attempt the two stages separately, with proper purification, so you can follow Barium's patent route with
the actual reagents instead of reaction mixtures. Try following the solvent volume in the patent examples unless the nitro/alcohol solution is truly
unworkable on its own.
And I'd encourage you to post still more elaborate details (as far as common sense allows, that is), such as equipment, exact procedure, and physical
description of the reaction at its different stages. The more info, the more likely someone will recognize an element that can be altered to make the
difference.
Well, good luck!
[Edited on 2007-6-8 by volfrahm]
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Klute
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Are you sure it's hydrogen gas that is generated? In the case of nitroarenes (which IMHO should apply to nitroalkanes), no hydrogen gas is said to be
generated as long as an acceptor is present, in a three-phases system. [1] Of course nitroarenes are much more easily reduced than nitroalkanes, but
it is still surprising.
Did you directly use the IPA solution obtained after the NaBH4 reduction as did Bandil, or did you isolate the nitroalkane before the CTH?
[1] Studies on the mechanism of Transfer Hydrogenation of nitroarenes by formate salts catalysed by Pd/C, H.Weiner, J.Blum, Y.Sasson J.Org.Chem, 56,
4481-4486 (1991) [very interesting read BTW]
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stoichiometric_steve
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volfrahm, as for purification of the nitroalkane, the nitroalkene was reduced separately using a solvent system of EtOAc in which were dissolved
substrate and NaBH4 slurried and water slowly dripped in, hydrolysis with acetic acid after reduction, water washing after hydrolysis, and rotary
evaporation of the solvent.
the nitroalkane itself was not further purified. after having it left to stand for a few weeks in the freezer, there was a white precipitate at the
bottom - most likely remaining borate salts.
8,5g of the the supernatant nitroalkane were added the 2-phase system of Pd/C, IPA and KCOOH which was prepared as follows: 16.5g KOH 85% p.a.
partially dissolved in IPA (~100ml), 13.5g HCOOH 85% tech. added, pH tested, some more drops HCOOH added until neutral. to this was added the catalyst
(BEFORE addition of nitroalkane) and an egg shaped stir bar. stirring and heating to reflux was started, reflux maintained for 14 hours.
tee hee! out of the trial following this procedure, 49% of amine salt were isolated.
[Edited on 10-8-2007 by stoichiometric_steve]
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Klute
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Congrats!
I wonder what made your succes this time. Maybe some impurities in the crude nitroalkane poisonned the catalyst when added before the formate in your
previous attempts? The Pd/C is a subtle animal..
When you prepared your formate solution, did it form two distinct layers (IPA+ aqu)? I find it unclear when you say:
| Quote: | Originally posted by stoichiometric_steve
were added the 2-phase system of Pd/C, IPA and KCOOH
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if the 2-phase system means solid catalyst + solution or isopropanolic+aqueuse solutions. I would guess solid+solution, but I want to be sure.
The problem could come from the hydride reduction, since the nitroalkane wasn't purified or characteritied, but that reduction usually seems to go on
easily and cleanly, from what was posted at the Hive.
I would really understand what causes your failures before, it seems to depend on very subtle parameters...
In any case, thanks for sharing your results
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Klute
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CTH succes
Barium's CTH method was tried with succes..
Nitrostyrene was made using GAA/Cyclohexylamine with 78% yield, and recrystallized with MeOH to afford nice yellow plates, single spot on TLC.
Nitroalkane was made by Barium's EtOAc/EtOH borohydride reduction, using 4 equivalents, and was isolated and recrystallized twice from MeOH to give
beautifull colorless needles, with an overall yield of 82%, single spot on TLC. A few mishabs during recrystallization must have causes some
mechanical losses (The solvant system MeOH/H2O was tried, but resulted in the nitroalkane oiling out during two attempts, so solution had be diluted,
extracted, and solvant removed again, two times.)
CTH reduction
0.17g of 10% Pd/C (Acros) were suspended in a little abs EtOH and pipetted into a schlenk under Argon, with magnetic stirring.
15 mL of abs EtOH were added with a syringe, followed by 7mmol of solid nitroalkane, under slight stirring.
3.00g (35.67 mmol) of solid HCOOK (very hygroscopic!) were added followed by 1,7mL (95.24 mmol, 2.67eq) of H2O, which caused immediate
evolution of H2, and solid KHCO3 appeared.
The schlenk was fitted with a condenser and placed in a 50°C oil bath, and stirring increased, the gas evoltuion (monitered by a wash bottle
connected to the top of the condneser) increased too, the stream of Argon was cut.
Small quantiites of GAA were added via syringe when the black suspension became too thick to be properly stirred. The oil bath was gradually
increased to 78°C, a mild reflux set in.
After 5h of reflux, the mixture was much more fluid and gas evoltuion had practically ceased. (It had drasticly dropped after about 2h). The oil
bath was removed, and the schlenk left to cool under Argon.
GAA was added under stirring in a ice bath until acidic (10mL, large excess) and the catalyst was vac filtered over normal filter paper, refiltered
on the same filter to clear up the slight purplish tint. The solution came out crystal clear after the second filteration. The catalyst was washed
with 10mL EtOH and 10ml H2O which where combined to the original filtrate. The catalyst was regenerated, see at the end.
The EtOH was distilled under light vacuum, at 45°C, until only water started to pass. The 30mL residu was diluted with 20mL dH2O, and washed with
2x15mL of DCM. The first wash had a amber tint (unreacted nitroalkane?), the second was clear.
The aq. was delicatefully basified with 20% NaOH, with 20mL DCM. The addition of the base caused cloudiness and an clear oil crashed out. As soon as
the cloudiness persisted, the pH was > 10. The DCM was seperated, and the aq. extracted with anothenr 2x20mL DCM.
The combined organics where washed with 2x25mL brine, dried, and the solvant was removed, the water-clear oil remaining was left under vacuum to
evaporate the solvant remains.
The amine base was diluted in10mL abs EtOH, and titrated with shaking with freshly prepared 10% w/vol H2SO4 in EtOH. This caused immediate
precipitation of a white solid. The pH was frequently checked with dampened pH paper, and titration stopped as soon as pH was acidic.
The white solid was vac filtered, washed with 10mL EtOH and 10mL anhydrous acetone, and dried under a lamp, to afford the amine in a yield of
62%.
catalsyt regeneration
Following US3214385, the catalyst was washed with 100ml of 10% NaOH, passed two times, then with ~50mL of dH2O until the washes had a pH of 8.5. It
was then dried under suction for 15min, and placed in a vial under argon.
Comments
The substarte was a sensitive one, but still gave very respectable yields, so this methods definatively works 
Even if certain of Barium's methods haven't always been reproductible (Thinking of the "wet reductive alkylation" with NaBH4 which I've personally
never seen/heard to give acceptable yields except by the author and another few), this one seems to be a efficient one. Few parameters could be
modified to obtain excellent yields IMHO.
It's surprising that just by changing to order of introduction of the reagents Stoechimetric_Steve passed from failure to succes, alot of parameters
could count.
BTW, I really recommend isolating and recrystallizing the nitroalkane between double bond reduction and CTH, the intial yellowish oil that solidifed
quickly contained some colored impurities that could possibly mess up the catalyst or interfer in one way or another. By recristallzing the
nitroalkane (if it's a solid!), on get's a pure product easily.
The final product will also be recrystallized although it seems to be very pure. The method of forming the sulfate salt, although satisfying,
may not be the more efficient solvant-wise. The filtrate will be evaporated to check if any dissolved product is present. IPA or perhaps AcOEt could
easily substitute for EtOH.
I don't know how vital the Argon atmospher is, but I prefer using it when I can, especially with the catalyst at the beggining; the gas evolution
during the reaction, if some sort of bubbler is used, prevents any air to come in on it's own.
I also don't know how effective the regeneration of the catalyst is, I'll try it some day to see. Unfortunaly, it contains some filter paper fibres
as it was scrapped off, I'll just compensate the weight next time I use it. Harder filter paper, or celite would be more avantageous i guess.
[Edited on 28-8-2007 by Klute]
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stoichiometric_steve
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in the meantime, i made the effort to distill the intermediate nitropropane. and boy, what a surprise: typically, the nitropropane from a NaBH4
reduction is a yellowish liquid, much lighter in color than the nitroalkene itself.
after distilling, the nitropropane came out colourless. there was a lot of reddish tarry residue in the distilling flask. the nitroalkane took on a
very slight pinkish colour upon standing in the freezer for 3 days.
i am currently running a 150mmol nitroalkane trial with 9g Pd/C 10%, 270:30ml MeOH:H2O, 50g NH4COOH (95%), slowly adding HCOOH 98% (34g) dropwise over
time to prevent carbonate deposition on the catalyst. the mix is argon flushed and mechanically stirred.
i am pretty sure the bad yields i previously got from Zn/HCOOH and CTH reductions were due to very impure nitroalkane, after seeing it distil as a
colourless liquid...
so, if you can afford a high vac pump (i was as lucky as can be and was donated a new edwards e2m1.5 which pulls down to 0,04torr when connected to a
still with 60cm vigreux), you should always distill the nitroalkanes after double bond reduction.
will report yields asap.
[Edited on 28-8-2007 by stoichiometric_steve]
[Edited on 28-8-2007 by stoichiometric_steve]
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Klute
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I think we can agree that isolating and purifying the intermediate nitroalkane is a necessary step to obtain descent yields...
If the nitroalkane is a liquid and a strong vacuum isn't availble, at least a few washes would be needfull IMO.
PS: I think the title could be changed
[Edited on 28-8-2007 by Klute]
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stoichiometric_steve
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WHATS THIS: when passing Ar thru the reaction mix, a large amount of fog is continuously generated. i took a tiny wiff at it and it
smelled sweetish (not ammoniacal or amine-like).
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JohnWW
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I doubt that there is any way that the argon could have reacted with the reaction mixture. The gas has recently been found to react with the greatest
difficulty only with F2, and that under the most extreme conditions, and by irradiation of its clathrate with frozen HF, forming HArF and ArF2.
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stoichiometric_steve
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i didnt expect the argon to react in any way, but quite obviously it displaces another component in the reaction mix. the question is WHICH?
[Edited on 29-8-2007 by stoichiometric_steve]
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Klute
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That's strange... was that with using IPA? Had you added any GAA yet?
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stoichiometric_steve
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Experiment 1:
9g of wet (probably 25% H2O) 10% Pd/C was introduced in a 3-neck 500ml RBF equipped with reflux condenser and an overhead stirrer.
150mmol of a previously distilled substituted phenyl-2-nitropropane (a water-clear liquid with a very slight pinkish tint) was added to wet the
catalyst.
270:30ml MeOH:H2O and 50g NH4COOH was added, stirring started, the mix was flushed with Argon (which produced the strange fumes mentioned above,
by apparently displacing some gaseous material dissolved in MeOH) and 34g HCOOH 98% was added dropwise over the course of the reaction (1 drop
every ~20 secs).
the reaction was allowed to stir for 24 hours.
addition of a bit of 20%w/w H2SO4 caused CO2 evolution and a white, flaky, voluminous precipitate appeared (this is your product!) which dissolved upon addition of water.
the workup should be done like this:
Filter the reaction mix through coarse filter paper twice without acidifying. rinse the filter cake generously with MeOH and add the washes to the
main filtrate.
the precipitate in the filter will be washed away with dH2O and kept separately.
the main MeOH/H2O filtrate probably needs to be filtered once more on fine filter paper which removes the rest of the suspended catalyst.
the catalyst wasn't regenerated as in previous runs, it was rinsed with MeOH and a bit of 20%w/w H2SO4, scraped from the filter paper with a spatula
and put in a small bottle. the filter paper, to which a lot of catalyst still stuck, was suspended and stirred with 3x 10ml dH2O to wash out some more
catalyst. this method produces a ready-to-use mix of catalyst along with the amount of water needed for another 150mmol batch. to get all of the
catalyst out, the bottle can be rinsed with MeOH.
acidify the filtrate and remove the MeOH in vacuo. combine both filtrates (make sure the combined filtrates are now acidic) and extract 3 times with
toluene (or something that pulls shit equally good...i just love it). basify and extract 3 times with toluene. dry toluene with Na2SO4, remove toluene
in vacuo et voilà!
i didnt get as far as to remove the toluene since it was pretty late already - so i dont know any yields. but: upon adding NaOH (aq. ~25%), there were
heavy milky clouds with droplets about 1mm in diameter rising to the liquid surface, forming a separate layer approximately 2mm*55mm²*pi = ~19ml . the freebase will be saved and distilled after another verification batch with the
recycled catalst has been run.
happy birthday.
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Klute
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That looks good
One question: Why do you (and alot of other writeups) acidify after you have filtered the catalyst?
Why not add dilute acid, a little water to dissolved any eventual precipitated product, filter and then strip the alcohol? I personally always feel
more confortable with the product as an salt doing work up, except when it's diluted in non-polar solvants of course.
I guess it less troublesome when using NH4OOCH, but with HCOOK, the solid KHCO3 could retain quite some product, even with a few alcohol washes
(which are going to be distilled afterwards), but if you acidify before filtering, you only have the fine catalyst to filter, and you have a fairly
concentrated aq. solution of the potassium salt of whatever acid you used to acidify wich makes work up easier IMHO. Evaporate alcohol under slight
vacuum, and when take off reduces and there's alot of bumping (as while trying to remove water from a concentrated solution of MeNH2.HCl or HCOOK, you
get the idea), perform an A/B, evaporate solvant, crystallize to your favorite salt, et voila.
Just my two (euro ) cents
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stoichiometric_steve
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| Quote: | Originally posted by Klute
One question: Why do you (and alot of other writeups) acidify after you have filtered the catalyst? |
it seems that the post reaction mix when using NH4COOH is in fact a basic solution with the alkylammonium carbonate salt dissolved,
so there is simply no point in acidifying at all. it just increases the volumes to handle. i need to give the reaction a second shot, but as
far as i can remember, the was no precipitate whatsoever before i added acid.
so basically, you would take the post rxn mix, do the workup as above and DO NOT acidify when you remove the MeOH in vacuo.
the acidification step is probably introduced to minimize losses due to the volatility of the amine, it being able to be distilled with steam.
the solution to your problem is: use NH4COOH. i dont know what the deal is with KCOOH, it is more expensive, you have to make it yourself, it is very
hygroscopic and insoluble in alcohols. what do i care if someone says it is a better hydride donor?
the ~25ml of slightly gold tinted freebase i got from the above attempt is, if i dare say that, as good as it can get. fack KCOOH
edit: a quick check was done, proving myself wrong thinking that dissolving amine freebase in acetone would form an imine: the
addition of 6M H2SO4 in Et2O caused instant deposition of a bright white precipitate.
[Edited on 30-8-2007 by stoichiometric_steve]
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Klute
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How bad is the Ammonium carbonate deposition in the condenser with Am.For as a donor? I've always heard it could plug the condenser if not removed
periodly, and having everything connect to Argon doesn't make that practical..
A few test runs with am.formate and HCOOK with same conditions could be usefull, even though most of the litterature considers
HCOOK>HCOON(R3)=HCOONH4>HCOONa>HCOOH.
In an article (1), Prasad et al. use catalytic amounts of base to convert introduced formic acid to a more effective
donor.
Cat. (0.1 eq) HCOOK gives 85% of reduction of an aromatic nitro compound, 0.1eq NaHCO3 gives the same yeild in slightly less time, but Et3N (0.1eq)
gives 100% in 20 minutes with 2 time less Pd/C loading. That could be worth a try with aliphatic nitros.. The formic acid is gradually added dropwise
over the course of the reaction.
I can scan the article if someone wants to give a look at it.
(1): Prasad et al., Adv. Synth. Catal. 2005.347, 1769-1773
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stoichiometric_steve
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| Quote: | Originally posted by Klute
How bad is the Ammonium carbonate deposition in the condenser with Am.For as a donor? |
there was no ammonium carbonate deposition whatsoever in my last run. this will most likely happen when you heat the reaction mix, but i dont see why
heating would be necessary.
i also dont know if argon flushing is vital for success in the reaction, you could always use N2 or CO2 for flushing, too. i'll try next time without
flushing. to make sure we both mean the same thing: you dont have Ar running thru the mix all the time! just for 30secs or so then disconnect it.
with alkali formates you always have the problem of a solid precipitate which potentially deactivates your catalyst during the course of the reaction.
this is not true for (alkyl)ammonium formates.
find attached Prasad et al., Adv. Synth. Catal. 2005.347, 1769-1773
Attachment: New Trends in Palladium-Catalyzed Transfer Hydrogenations Using Formic Acid.pdf (81kB)
This file has been downloaded 1788 times
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Klute
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Well great, no need of scanning the article
I didn't realize you conducted the reaction at room temp! That's something solved...
And yes, I only flush the flask at the beggining, leave a little stream when the reagents are introduced, and then shut it off. Argon is expensive,
I'm not to keen on sending some in the atmospher just for the sake of it
I frequently neutralize the bicarbonate with GAA, but it could effectively cover some catalyst surface... And the problem of reteiving palladium in
the final salt mentionne din the article isn't too reassuring..
You've convinced me, I'll give ammonium formate a try on of these days!
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