Sciencemadness Discussion Board

Pd/C H2-gas reduction of ß-nitrostyrenes

Palladium - 24-5-2011 at 08:04


The reduction of ß-nitrostyrenes resulting in a phenetylamine, PEA. This is not the methylated PEA I'm purposing on, PEA is substance found in chocolate and is sold as nutrition.


References

We can take a look at this report which performing a reduction of ß-nitrostyrenes under very mild conditions:

http://www.lycaeum.org/rhodium/chemistry/ns.hydrogenation.ht...


Experiments

1. I followed the example in the link exactly, but used a normal 5% Pd/C catalyst, not in the report mentioned "5% Pd/C K-type" - which I can't find any further information about anywhere. I can tell you flat out that this process doesn't work - at least not with a normal Pd/C catalyst. Notice that they are using relatively large amounts of catalyst (200 g Pd/C 5% per mole PEA), probably because the Pd/C is undermined in efficiency at 0 °C compared to higher temperatures. I tried this reduction at 2-5 °C in EtOH and HCl (aq) at 1 atm H2-pressure in 3 h. No noticeable reaction; in fact, all of the ß-nitrostyrene was left when solvent was removed - and after heating much of this will polymerize.

2. This time from 50 °C the first half of time and up to 90 °C the second half, at 2 atm pressure but without HCl (aq). Reaction worked satisfactionally, but I haven't counted on the yields accurately.


Discussion

ß-nitrostyrenes are sensitive for heat and pressure What I have heard is that normally the yield is only around 50% to the corresponding PEA. I understand that higher temperatures will polymerize the ß-nitrostyrene - but not very fast - especially at 90 °C, where Pd/C works best (Pd absorbs more than 900 times its own volume of hydrogen at 90 °C).

Pd/C in acidic solution After reading several Pd/C reductions I can't see anywhere that this is performed in acidic solutions, except when it works as a promoter to form an ester - which is the case in a OH-reduction. I counted pH for the solution in the link to 0,5 - very acidic, isn't it? Too much acid can cause different types of tar, but didn't occur in my case at cold conditions.

Amount of solvent This process in the link also used very much solvent (3,9 L per mole PEA), which I also found not necessary. Too less solvent is not good, but I have an idea of using 1L EtOH per mole PEA.


Questions

1. What undesired reaction tends to happen to the ß-nitrostyrenes at higher H2-pressures?

2. Why would HCl in this solution promote the reduction?

3. Any idea about the minimum amount of solution in these reductions?

4. How would the ß-nitrostyrene respond to a Pt02-catalyst?

hissingnoise - 24-5-2011 at 10:15

There's some quite interesting stuff on β-nitrostyrene and its derivatives here.


Nicodem - 24-5-2011 at 10:58

Quote: Originally posted by Palladium  

1. I followed the example in the link exactly, but used a normal 5% Pd/C catalyst, not in the report mentioned "5% Pd/C K-type" - which I can't find any further information about anywhere. I can tell you flat out that this process doesn't work - at least not with a normal Pd/C catalyst.

I don't understand why it would not work for beta-nitrostyrene when it works for methoxy substituted beta-nitrostyrenes. How sure you are you that your Pd-C is still active? How did you verify the purity and identity of your beta-nitrostyrene? Is your HCl free of H2S?

Quote:
Notice that they are using relatively large amounts of catalyst (200 g Pd/C 5% per mole PEA), probably because the Pd/C is undermined in efficiency at 0 °C compared to higher temperatures. I tried this reduction at 2-5 °C in EtOH and HCl (aq) at 1 atm H2-pressure in 3 h. No noticeable reaction; in fact, all of the ß-nitrostyrene was left when solvent was removed - and after heating much of this will polymerize.

As the experimenters at the Hyperlab forum demonstrated, the amount of the catalyst can be reduced to 5 mol% (or even less, highly depending on the substrate) and still obtaining good yields provided you use pressure in the range of 2-5 bar and start with a cold mixture. My memory is not very good, but I think they used slightly above 1 equivalent of conc. HCl in methanol. I do well remember that lots of substrates have been tested and no reports of failure mentioned. Check by yourself as I have no time to search info for you. I remember there is also an example of an arylacetonitrile hydrogenation with Pd-C. Most posts are in English so you should have no troubles with the search engine.

Anyway, the HCl is used to prevent the formation of secondary amines by in situ amine protection. Secondary amines form during the reduction of oximes and nitriles in the absence of added acid (see Hydrogenation Methods by Rylander). Since the reduction of beta-nitrostyrenes gives first the phenylacetaldoximes which are then the difficult ones to reduce (can be even preparatively isolated in good yields as is described in some articles), the acid can cause troubles due to partial oxime hydrolysis, especially if the temperature is higher. Aldoximes reduce slowly with Pd-C (contrary to their reduction with Raney nickel which is very fast) while, as far as I know, ketoximes are nearly impossible to hydrogenate with Pd-C. This slow reduction step is probably the reason for the high dependence of yields on the catalyst loading. If there is not enough Pd-C, much of the oxime intermediate hydrolyzes before getting reduced to the amine. I'm mostly guessing from the results described in the few articles on the topic, that I read (years ago, so don't rely to much on what I say).

Palladium - 24-5-2011 at 14:30



Quote:

I don't understand why it would not work for beta-nitrostyrene when it works for methoxy substituted beta-nitrostyrenes. How sure you are you that your Pd-C is still active? How did you verify the purity and identity of your beta-nitrostyrene? Is your HCl free of H2S?


I believe it works, but maybe the reason is because they have a "K-type" Pd/C catalyst? I don't have and I don't know what K-type is.

I'm very sure that the Pd/C works, and I know how to test it before. It's also pre-reduced and then tested before I start the reduction. Stirring was excellent.

The ß-nitrostyrene was highly purified through crystallization the day before.



Quote:

Aldoximes reduce slowly with Pd-C (contrary to their reduction with Raney nickel which is very fast) while, as far as I know, ketoximes are nearly impossible to hydrogenate with Pd-C.


I believe Ni/C do this reduction of ketoximes almost as well as RaNi, at least better than Pd/C?

However, thanks a lot for your answers.


Vogelzang - 24-5-2011 at 15:33

What do you think of this patent?
http://www.google.com/patents?id=G3AcAAAAEBAJ&printsec=a...

Melgar - 24-5-2011 at 21:24

Does anyone think it's a good idea to prepare my own Pd/C? I have some PdCl2 solution and activated carbon.

Palladium - 25-5-2011 at 04:23

Quote: Originally posted by Melgar  
Does anyone think it's a good idea to prepare my own Pd/C? I have some PdCl2 solution and activated carbon.


You almost can't failure that process. Just buy some cheap "Norit" activated carbon, and reflux this in 10% HNO3 (aq) for 3 h. Then you wash this with H2O several times until pH is neutral and then a few times more.

Then you solve NaAc in H2O together with pre-dissolved PdCl2 into an hydrogenation vessel, and add the HNO3-washed charcoal. Hydrogenate this with agitation until absorption ends. Filter off and wash several times with H2O. Drying isn't necessary of one rinse a few times with EtOH under inert atmosphere. If it's not inert avoid using EtOH at all, otherwise it's a great way to start a fire.

Palladium - 25-5-2011 at 12:06



Quote:

Anyway, the HCl is used to prevent the formation of secondary amines by in situ amine protection. Secondary amines form during the reduction of oximes and nitriles in the absence of added acid (see Hydrogenation Methods by Rylander). Since the reduction of beta-nitrostyrenes gives first the phenylacetaldoximes which are then the difficult ones to reduce (can be even preparatively isolated in good yields as is described in some articles), the acid can cause troubles due to partial oxime hydrolysis, especially if the temperature is higher.


I don't have detailed literature or sources about Pd/C, but I know its life if different depending on what it's used to - of course. At least 4-5 times according to some producers of Pd/C.

How about when the Pd/C is used in HCl (aq)? I guess the PdCl2 is dissolves out from C in that case, but not in e.g. GAA as the only acid in solution. I heard from someone that Pd/C is not reusable without processing after one time when a strong acid was present in a reduction. Is the Pd solved out when using HCl at pH below 1 in solution? Is this negligible when only GAA is the acid?



Nicodem - 25-5-2011 at 13:22

I have never really reused Pd-C. It is more or less one use only under laboratory conditions. It can however be reactivated. I think it can be done by washing with alcohols, then NaOH(aq) or NH3(aq) and plenty of water. I don't see why palladium leaching would be much of a problem with HCl. The chloride anions are quite good ligands for Pd(II), but as far as I know they are not good enough for Pd(0). Though Pd-C tends to leach lots of Pd as colloidal particles in any solvent.

Quote:
I believe it works, but maybe the reason is because they have a "K-type" Pd/C catalyst? I don't have and I don't know what K-type is.

The posts at Hyperlab mention no special type of Pd-C. I believe the generic 5% Pd-C as can be found in any lab was used, or else the experimenters would specify it and I would certainly remember such a peculiarity. Your failure in repeating the literature method is most likely connected with other factors. Try the reaction on p-methoxy-beta-nitrostyrene or some other substrate that is verified in that Bull. Chem. Soc. Jpn. article. If you still don't succeed, then something is wrong with either one of the reactants/solvents/catalyst/HCl you use, or your technique.

Vogelzang - 25-5-2011 at 16:21

http://www.sciencemadness.org/talk/viewthread.php?tid=12792

Melgar - 26-5-2011 at 09:43

Quote: Originally posted by Palladium  
Quote: Originally posted by Melgar  
Does anyone think it's a good idea to prepare my own Pd/C? I have some PdCl2 solution and activated carbon.


You almost can't failure that process. Just buy some cheap "Norit" activated carbon, and reflux this in 10% HNO3 (aq) for 3 h. Then you wash this with H2O several times until pH is neutral and then a few times more.

Then you solve NaAc in H2O together with pre-dissolved PdCl2 into an hydrogenation vessel, and add the HNO3-washed charcoal. Hydrogenate this with agitation until absorption ends. Filter off and wash several times with H2O. Drying isn't necessary of one rinse a few times with EtOH under inert atmosphere. If it's not inert avoid using EtOH at all, otherwise it's a great way to start a fire.

Thanks. I have some Norit activated carbon already actually, I just need to acquire some nitric acid. The only thing is, I'm not sure how pure or what concentration my PdCl2 solution is. Some calcium chloride and sulfuric acid got in the solution by accident, but only a very small amount. It's a pretty opaque reddish-brown, but I doubt that indicates much. You think I should just guess, or is there an easy way to measure the concentration? Maybe by how much hydrogen it takes to reduce the PdCl2 to Pd?

Palladium - 27-5-2011 at 10:54

Quote: Originally posted by Melgar  
Quote: Originally posted by Palladium  
Quote: Originally posted by Melgar  
Does anyone think it's a good idea to prepare my own Pd/C? I have some PdCl2 solution and activated carbon.


You almost can't failure that process. Just buy some cheap "Norit" activated carbon, and reflux this in 10% HNO3 (aq) for 3 h. Then you wash this with H2O several times until pH is neutral and then a few times more.

Then you solve NaAc in H2O together with pre-dissolved PdCl2 into an hydrogenation vessel, and add the HNO3-washed charcoal. Hydrogenate this with agitation until absorption ends. Filter off and wash several times with H2O. Drying isn't necessary of one rinse a few times with EtOH under inert atmosphere. If it's not inert avoid using EtOH at all, otherwise it's a great way to start a fire.

Thanks. I have some Norit activated carbon already actually, I just need to acquire some nitric acid. The only thing is, I'm not sure how pure or what concentration my PdCl2 solution is. Some calcium chloride and sulfuric acid got in the solution by accident, but only a very small amount. It's a pretty opaque reddish-brown, but I doubt that indicates much. You think I should just guess, or is there an easy way to measure the concentration? Maybe by how much hydrogen it takes to reduce the PdCl2 to Pd?


I would rinse PdCl2 from CaCl2 and H2SO4 first. I'm not quite sure, but I think this process would work: Evaporate the solution with PdCl2 completely with heat. Chop up the solid with a mortar-and-pestle-set to dust. Reflux this dust in EtOH/IPA (CaCl2 is soluble in alcohol) a moment and filter off. Dry the solid again and dissolve it in HCl (aq), evapore to almost dryness, add more HCl - reapeat this a few times and lastly dry completely. Weight the solid, which should be only PdCl2. Maybe one day of work but Pd is expensive nowadays.

I don't know the amount H2 it takes, but I would give the pre-reduction more pressure than 1 atm to 2 atm. Someone can correct me if I'm wrong about the pressure of pre-reduction, but I think it's similar to PtO2 (2 atm).

If you don't have H2-gas just build your own generator and accumulate it in another tank. One day of work.

Palladium - 28-5-2011 at 11:45

Sorry, I had wrong about rinse PdCl2 from CaCl2 through dissolve CaCl2 in EtOH. PdCl2 is also soluble in alcohols, so just forget what I wrote in the previous post.


Melgar - 30-5-2011 at 05:08

I'm guessing that the H2SO4 probably reacted with the CaCl2 to form insoluble CaSO4. Either that or the CaCl2 reacted with the PdCl2 to form calcium tetrachloropalladate, if that's possible. Anyway, I made some nitric acid then cleaned and rinsed my carbon, so I'm almost ready for the hydrogenation part.

I'm thinking after I hydrogenate the palladium chloride, I'll just rinse the stuff with water a few times to get any of those salts off. I don't have a source of EtOH, so I'll probably use MeOH. I can use isopropyl alcohol too, but I have more MeOH and it's cheaper. Plus, its properties are closer to EtOH.

jwarr - 30-5-2011 at 15:51

Palladium: you mention Pd/C being relatively easy to prepare, but Sunlight posted extremely poor results for a CTH reduction when using their own Pd/C. Do you think it was just an error in their preparation?

Palladium - 2-6-2011 at 08:12

Quote: Originally posted by Melgar  
I'm guessing that the H2SO4 probably reacted with the CaCl2 to form insoluble CaSO4. Either that or the CaCl2 reacted with the PdCl2 to form calcium tetrachloropalladate, if that's possible. Anyway, I made some nitric acid then cleaned and rinsed my carbon, so I'm almost ready for the hydrogenation part.

I'm thinking after I hydrogenate the palladium chloride, I'll just rinse the stuff with water a few times to get any of those salts off. I don't have a source of EtOH, so I'll probably use MeOH. I can use isopropyl alcohol too, but I have more MeOH and it's cheaper. Plus, its properties are closer to EtOH.


MeOH works fine also. In some cases with Pd/C the conditions should be changed depending on what solvent used. For example, the range for MeOH is preferred to be 25 < C < 50 but in the same reaction with EtOH it is 45 < C < 80.

In some cases, with reduction with PtO2, the time for a reduction to complete takes three times with MeOH than with EtOH.

Even though you don't have pure PdCl2, I think it's worth a try. I believe - nut not sure - that the reduction of PdCl2 to Pd(0) will affix the Pd but not the other salts. This is only my guess.

To wash the Pd/C, I used only H2O. That catalyst worked fine, but I can't promise it couldn't work better. Nicodem has far more knowledge than me, and he mentioned to wash after reduction (not after pre-reduction) with NaOH/H2O. Personally, I wash first with EtOH, then with toluene, then with EtOH again until the liquid gets clear.

I'm also going to do a reduction with GAA instead of HCl (aq) these days. I'll write about this soon.

Palladium - 2-6-2011 at 08:19

Quote: Originally posted by jwarr  
Palladium: you mention Pd/C being relatively easy to prepare, but Sunlight posted extremely poor results for a CTH reduction when using their own Pd/C. Do you think it was just an error in their preparation?


What molecule was reduced?

azo - 4-6-2011 at 02:55

Hi everyone i have a question thats not related to catalytic transfer hydrogenations but i didn't think it should have a new thread started for it.
This has been troubling me for some time so i thought i would ask someone with more knowledge than me.
In relation to the reduction of beta unsaturated nitro compound
(ex) phenyl 2 nitropropene ,i understand that the reduction with metal salts or acid and metal affords oximes, and that the reduction with metal and ammonium chloride forms hydroxylamines but what i don't understand is why amalgams or catalytic hydrogenations reduce nitroalkenes directly to amines ,my thoughts are that the nitroalkene gets attracted to the surface of the catylist where it joins the hydrogen to the double bond which stops the formation of oximes .
could someone explain whether i am wrong and explain why this happens.
And why is this not the case with terminal nitroalkenes.


regards azo

[Edited on 4-6-2011 by azo]

Nicodem - 4-6-2011 at 06:14

Quote: Originally posted by azo  
and that the reduction with metal and ammonium chloride forms hydroxylamines

Could please give the reference where a reduction of any 2-nitropropene to a hydroxylamine is described using such a metal dissolving reaction? That would be quite useful.
Quote:
my thoughts are that the nitroalkene gets attracted to the surface of the catylist where it joins the hydrogen to the double bond which stops the formation of oximes .

If the double bond would be the first to reduce, then oximes would not be intermediates, wouldn't they? It would be unusual for such a highly electron poor double bond to be hydrogenated faster than the nitro group when using Pd-C. The oximes are intermediates, most probably exactly because the double bond refuses to get hydrogenated as rapidly (N-hydroxyenamines are tautomeric to oximes!).
Quote:
And why is this not the case with terminal nitroalkenes.

I already gave a plausible explanation above thread. Aldoximes reduce much more easily with Pd-C. Ketoximes require either too harsh conditions, or more apropriate catalysts (like Raney Ni or Rh-C). See the conditions listed in the patent US3458576 cited above by Vogelzang and compare that to the conditions used in the Bull. Chem. Soc. Jpn. article.
By the way, aluminium amalgam reduces both, aldoximes and ketoximes, extremely easily, so I guess this answer also your other question.

azo - 4-6-2011 at 23:50

Thank you for clearing that up for me nicodem now it makes sence greatly appreciated for your responce.

REGARDS AZO

Palladium - 5-6-2011 at 07:40


Anyone knows how much the pressure of H2 influences the reaction using 5% Pd/C? Of course it does, but I'm more thinking of e.g. 30 psi when it's preferred with 60 psi - can I compensate this with longer reaction time instead? Too much pressure I can imagine sometimes will crush the molecule to an undesired product (hydrogenolysis instead of hydrogenation), but in cases when the H2-pressure is lower than preferred, and I simply drive the reaction until no more H2 is adsorbed - what risk might appear?



Nicodem - 5-6-2011 at 12:42

It pretty much depends on what you are hydrogenating. For example, if you are hydrogenating an isolated olefinic double bonds which reduces already at 1 atm, increasing the pressure is not going to help much. Nitroarenes also don't need increased pressure and 1 atm does just fine. But if you are reducing groups difficult to reduce using Pd-C (e.g., nitriles, oximes, debenzylations, some aryl alkyl ketones, dechlorinations), then it is well worth speeding up the reaction by increasing the pressure. But in essence, whatever works in a Parr shaker apparatus (designed for 60 PSI = 4.14 bar) will work also using a balloon as long as you load it up with some more catalyst (and/or use the 10% Pd-C) to compensate for the slowing down.

On the other hand, hydrogenations in autoclaves at >100 bar with heating up are something quite different. Usually things that refuse to get hydrogenated in a good ol'shaker apparatus, will eventually give up under such forcing conditions. But these are usually employed when using catalysts like copper chromite, or for the reduction of benzene rings with Ni or Pt based catalysts.

For the more common transformations, you can always choose a more appropriate catalyst instead of forcing conditions. For example, if neutral or basic conditions are tolerated, you can often choose Raney Nickel over Pd-C. As an example, nitriles reduce sluggishly with Pd-C in the presence of HCl, but the same transformation can be performed better with Raney Ni in the presence of ammonia at the same pressure. Furthermore, since the Raney Ni is cheap, you can use lots of it, thus making the reaction proceed faster at a much lower pressure.

In the case of beta-nitrostyrenes, I would expect a slight complication when the reaction is too slow. Lowering the pressure without increasing the catalyst load, will slow down the hydrogenation, but it will not slow down any side reactions that do not involve hydrogen (like the hydrolysis of some intermediate, for example). I believe this might be the reason why the Japonese authors perform the reaction at 0 °C. I also believe this is why, in the above mentioned patent, increased temperatures can be used to force the reaction on a nitropropene - no acid is being used. This probably reduces the selectivity for the primary amine, but at least it allows for harsher conditions. The claim that the reduction goes better with a mixture of Ni and Pd based catalysts might have a rationale as well. The Pd catalyst might reduce to a certain stubborn intermediate which is on turn further reduced by the Ni catalyst (the oxime?).

smuv - 6-6-2011 at 07:59

Another good thing about raney nickel is you can do reductions on dirtier starting materials without as much worry about poisoning. It takes very little 'poison' to stop a few 10's of mgs of Pd in it's tracks, but the large quantities of raney nickel that are use make poisoning less of an issue.

azo - 7-6-2011 at 00:17

After studying about the preparation of rainey nickel i was supprised to no that there is additional metals like zinc cessium and others added as a catylist promotor.And i have to ask myself what happens to the promotor metal during the leaching of the aluminium when treated with sodium hydroxide.
This in some way must also activate the promotor catylist as well.
And ovuesly the leaching process is directly related to the amount of hydrogen that the rainey nickel can carry on its surface which would tell me that you would be limited on what acid or base that would be used during the hydrogenation.
It appears to me that the preparation of the catylist don't seem to be that hard if one had a high tempurature furnace.
There also seems to be endless different types of rainey nickel that can be prepaired.
So i haved added this patent to provide further information.


regards azo

Attachment: Raney nickel catalysts, a method for producing said raney nickel catalysts and the use of the same for hydrogenating org (255kB)
This file has been downloaded 2891 times


Palladium - 7-6-2011 at 05:11

Quote: Originally posted by azo  
After studying about the preparation of rainey nickel i was supprised to no that there is additional metals like zinc cessium and others added as a catylist promotor.And i have to ask myself what happens to the promotor metal during the leaching of the aluminium when treated with sodium hydroxide.
This in some way must also activate the promotor catylist as well.
And ovuesly the leaching process is directly related to the amount of hydrogen that the rainey nickel can carry on its surface which would tell me that you would be limited on what acid or base that would be used during the hydrogenation.
It appears to me that the preparation of the catylist don't seem to be that hard if one had a high tempurature furnace.
There also seems to be endless different types of rainey nickel that can be prepaired.
So i haved added this patent to provide further information.


regards azo



I don't see the preparation of RaNi as the challange, even though it seems not to be easy. The agitation is not possible with magnetic stirring with RaNi; it must be performed in a shaker. This reactor must also have simultaneous heating in addition to agitation. Also, the pressure required is very high.

Palladium - 8-6-2011 at 03:13

Quote: Originally posted by Nicodem  
It pretty much depends on what you are hydrogenating. For example, if you are hydrogenating an isolated olefinic double bonds which reduces already at 1 atm, increasing the pressure is not going to help much. Nitroarenes also don't need increased pressure and 1 atm does just fine. But if you are reducing groups difficult to reduce using Pd-C (e.g., nitriles, oximes, debenzylations, some aryl alkyl ketones, dechlorinations), then it is well worth speeding up the reaction by increasing the pressure. But in essence, whatever works in a Parr shaker apparatus (designed for 60 PSI = 4.14 bar) will work also using a balloon as long as you load it up with some more catalyst (and/or use the 10% Pd-C) to compensate for the slowing down.

On the other hand, hydrogenations in autoclaves at >100 bar with heating up are something quite different. Usually things that refuse to get hydrogenated in a good ol'shaker apparatus, will eventually give up under such forcing conditions. But these are usually employed when using catalysts like copper chromite, or for the reduction of benzene rings with Ni or Pt based catalysts.

For the more common transformations, you can always choose a more appropriate catalyst instead of forcing conditions. For example, if neutral or basic conditions are tolerated, you can often choose Raney Nickel over Pd-C. As an example, nitriles reduce sluggishly with Pd-C in the presence of HCl, but the same transformation can be performed better with Raney Ni in the presence of ammonia at the same pressure. Furthermore, since the Raney Ni is cheap, you can use lots of it, thus making the reaction proceed faster at a much lower pressure.

In the case of beta-nitrostyrenes, I would expect a slight complication when the reaction is too slow. Lowering the pressure without increasing the catalyst load, will slow down the hydrogenation, but it will not slow down any side reactions that do not involve hydrogen (like the hydrolysis of some intermediate, for example). I believe this might be the reason why the Japonese authors perform the reaction at 0 °C. I also believe this is why, in the above mentioned patent, increased temperatures can be used to force the reaction on a nitropropene - no acid is being used. This probably reduces the selectivity for the primary amine, but at least it allows for harsher conditions. The claim that the reduction goes better with a mixture of Ni and Pd based catalysts might have a rationale as well. The Pd catalyst might reduce to a certain stubborn intermediate which is on turn further reduced by the Ni catalyst (the oxime?).


I would like to ask one thing about the solvent used in hydrogenation. I know it works with a number of solvents, but I thinking of if some denaturants can affect the reaction. In my case the denaturant is 2-butanone. I have problems to believe this would make any difference, but I will still exclude this suspicion.


azo - 19-6-2011 at 14:53

here is some further information on this and explains why normal pdc is not very usefull

regards azo:D

Attachment: US3328465.pdf (447kB)
This file has been downloaded 785 times


Palladium - 20-6-2011 at 12:33

Quote: Originally posted by azo  
here is some further information on this and explains why normal pdc is not very usefull

regards azo:D


Thanks a lot for this. Pd/C is king when it comes to OH-reduction I suppose, but still sensitive.

I will build my setup for Raney Nickel reduction. The melting isn't that difficult, and not the agiator either. 80 bar pressure isn't so much anyway. Still, it is a lot of work. After a lot of research on RaNi I find that this catalyst is essential and high-yielding in many cases. Surprisingly cheap catalyst also, probably possible to reuse also.


azo - 23-6-2011 at 03:13

Here is a little on urishabara palladium


regards azo:D

Attachment: urushibara.html (72kB)
This file has been downloaded 1114 times


Templar - 28-12-2014 at 05:42

Quote: Originally posted by Nicodem  
Quote: Originally posted by Palladium  

1. I followed the example in the link exactly, but used a normal 5% Pd/C catalyst, not in the report mentioned "5% Pd/C K-type" - which I can't find any further information about anywhere. I can tell you flat out that this process doesn't work - at least not with a normal Pd/C catalyst.

I don't understand why it would not work for beta-nitrostyrene when it works for methoxy substituted beta-nitrostyrenes. How sure you are you that your Pd-C is still active? How did you verify the purity and identity of your beta-nitrostyrene? Is your HCl free of H2S?

Quote:
Notice that they are using relatively large amounts of catalyst (200 g Pd/C 5% per mole PEA), probably because the Pd/C is undermined in efficiency at 0 °C compared to higher temperatures. I tried this reduction at 2-5 °C in EtOH and HCl (aq) at 1 atm H2-pressure in 3 h. No noticeable reaction; in fact, all of the ß-nitrostyrene was left when solvent was removed - and after heating much of this will polymerize.

As the experimenters at the Hyperlab forum demonstrated, the amount of the catalyst can be reduced to 5 mol% (or even less, highly depending on the substrate) and still obtaining good yields provided you use pressure in the range of 2-5 bar and start with a cold mixture. My memory is not very good, but I think they used slightly above 1 equivalent of conc. HCl in methanol. I do well remember that lots of substrates have been tested and no reports of failure mentioned. Check by yourself as I have no time to search info for you. I remember there is also an example of an arylacetonitrile hydrogenation with Pd-C. Most posts are in English so you should have no troubles with the search engine.

Anyway, the HCl is used to prevent the formation of secondary amines by in situ amine protection. Secondary amines form during the reduction of oximes and nitriles in the absence of added acid (see Hydrogenation Methods by Rylander). Since the reduction of beta-nitrostyrenes gives first the phenylacetaldoximes which are then the difficult ones to reduce (can be even preparatively isolated in good yields as is described in some articles), the acid can cause troubles due to partial oxime hydrolysis, especially if the temperature is higher. Aldoximes reduce slowly with Pd-C (contrary to their reduction with Raney nickel which is very fast) while, as far as I know, ketoximes are nearly impossible to hydrogenate with Pd-C. This slow reduction step is probably the reason for the high dependence of yields on the catalyst loading. If there is not enough Pd-C, much of the oxime intermediate hydrolyzes before getting reduced to the amine. I'm mostly guessing from the results described in the few articles on the topic, that I read (years ago, so don't rely to much on what I say).


nicodem, would you be able to provide clues as to the wherabouts of the experimental trials undertaken at the hive? I cannot find any, only reference to the atmospheric reduction undertaken at the start of the thread.

Nicodem - 29-12-2014 at 07:54

Quote: Originally posted by Templar  
nicodem, would you be able to provide clues as to the wherabouts of the experimental trials undertaken at the hive? I cannot find any, only reference to the atmospheric reduction undertaken at the start of the thread.

I can only assume that I meant Hyperlab when I referred to Hyperlab. Where did you see The Hive mentioned? That forum is dead for 10 years already.
Quote: Originally posted by Nicodem  
As the experimenters at the Hyperlab forum demonstrated...

zed - 29-12-2014 at 15:03

These reductions run well in glacial acetic with an equivalent of H2SO4 added.

[Edited on 29-12-2014 by zed]

Templar - 29-12-2014 at 15:28

Sorry, that was a small typo. I did mean hyperlab.

zed - 29-12-2014 at 16:00

You are assuming that such experiments were actually performed?

That may be an error. Some of the experiments reported on the "Hive" as dreams, were just that....dreams. Pipe dreams to be more exact.

B Nitropropenyl benzenes, also polymerize during the reduction. Since no aldehydes and no amines are formed during the initial stages of the reduction, it clearly isn't formation of secondary amines , but is some other phenomena.

Without temperature control, a solvent consisting of 50/50 methanol- glacial acetic acid, will produce about a 50/50 yield. 50% Oxime, 50% brown crud.

With temperature control, utilizing Glacial acetic acid and an equivalent of H2SO4; yields of Oxime appear to be ~90%, without traces of crud. Product solutions are basically colorless. This is using a "Brown" type Pt as catalyst.

[Edited on 30-12-2014 by zed]

[Edited on 30-12-2014 by zed]

Templar - 29-12-2014 at 16:19

Quote: Originally posted by zed  
You are assuming that such experiments were actually performed?

That may be an error. Some of the experiments reported on the "Hive" as dreams, were just that....dreams. Pipe dreams to be more exact.


Yes. I did sort of guess that. It sounded like they had been completed experimentally and that someone had read them. I cannot find them; but Ihave a hunch that there are some sections of that forum I cannot see.

I am trying to sort a hydrogen regulator. Getting prices of $300-500! Im in NZ. So I will need to find one overseas maybe that will be compatible with the canister threads available.

The next issue to sort will be a suitable vessel. A friend of mine suggested that a pressurized vessel like a weed sprayer could be useable. I want to try and find pressure rating for them; easier said than done.

I think the main issue here isnt so much a tough container as it is finding one that can be modified for the fittings off the h2 canister.

I was shown a fairly basic but effective shaker design, so I will run with that.

So zed, you are reporting oximes instead of amines?

[Edited on 30-12-2014 by Templar]

zed - 29-12-2014 at 16:27

Hnuh? You are actually gonna try it? You need a Rabbi...a mentor. Depending on what exactly you wish to do, you may need a permit. The experiment is easily performed, with a little platinum, a few bucks worth of chemicals, a flask, a balloon, etc.

Templar - 29-12-2014 at 16:39

Quote: Originally posted by zed  
Hnuh? You are actually gonna try it? You need a Rabbi...a mentor. Depending on what exactly you wish to do, you may need a permit. The experiment is easily performed, with a little platinum, a few bucks worth of chemicals, a flask, a balloon, etc.


Ah, well I was hoping on running a low pressure setup at around 3 or 4 bar gauge.

The costs right now are looking a little bit prohibitive though.

I probably wont get involved with any rabbis. I think they have a reputation for doing strange things with young handsome men :o

Its sounding like oximes are obtained at atmospheric pressure using GAA and sulfuric acid? but the oxime is reduced to amine under additional pressure.

Nicodem - 30-12-2014 at 02:27

Quote: Originally posted by Templar  
So zed, you are reporting oximes instead of amines?

Just as the literature does. The hydrogenation of alpha-substituted nitroolefins over Pd-C to obtain ketoximes is a known synthetic method. Pt catalyst behave similarly.
Quote: Originally posted by Templar  
Its sounding like oximes are obtained at atmospheric pressure using GAA and sulfuric acid? but the oxime is reduced to amine under additional pressure.

Depends which oximes and what catalyst, not so much the pressure. Good luck in reducing regular ketoximes over Pd or Pt catalysts. It can happen to some extent in some cases, but it is not worth optimizing given the alternatives. Even aldoximes are slow to hydrogenate over Pd-C, let alone the ketoximes. Read some literature on hydrogenations. There is a very good book on the topic: Catalytic Hydrogenation in Organic Syntheses by A. Rylander. I suggest you read it thoroughly before you waste time reinventing the wheel (or you injure yourself).
Quote: Originally posted by Templar  
Sorry, that was a small typo. I did mean hyperlab.

Did you search there at all? It does not look like you tried at all. Just by using the keyword "hydrogenation" I got plenty of experimental examples. The most relevant ones are in the thread #514228 and post #550718. There is more in the Development crew forum section. And I only looked for English language. There must be much more to be found with some more effort.

[Edited on 30/12/2014 by Nicodem]

zed - 31-12-2014 at 15:47

Start small. Aim for a few grams of product. Most experiments fail. Even when there are reliably recorded procedures, a positive outcome is no certainty.

Baby steps. You knew for example, that gauges used with Hydrogen must meet certain materials specifications? Yup. Some gauges have the right kind of guts, some don't. With the wrong kind of innards, your gauges will probably still work, but not for very long.

Templar - 31-12-2014 at 20:48

Quote: Originally posted by Nicodem  
Quote: Originally posted by Templar  
So zed, you are reporting oximes instead of amines?

Just as the literature does. The hydrogenation of alpha-substituted nitroolefins over Pd-C to obtain ketoximes is a known synthetic method. Pt catalyst behave similarly.
Quote: Originally posted by Templar  
Its sounding like oximes are obtained at atmospheric pressure using GAA and sulfuric acid? but the oxime is reduced to amine under additional pressure.

Depends which oximes and what catalyst, not so much the pressure. Good luck in reducing regular ketoximes over Pd or Pt catalysts. It can happen to some extent in some cases, but it is not worth optimizing given the alternatives. Even aldoximes are slow to hydrogenate over Pd-C, let alone the ketoximes. Read some literature on hydrogenations. There is a very good book on the topic: Catalytic Hydrogenation in Organic Syntheses by A. Rylander. I suggest you read it thoroughly before you waste time reinventing the wheel (or you injure yourself).
Quote: Originally posted by Templar  
Sorry, that was a small typo. I did mean hyperlab.

Did you search there at all? It does not look like you tried at all. Just by using the keyword "hydrogenation" I got plenty of experimental examples. The most relevant ones are in the thread #514228 and post #550718. There is more in the Development crew forum section. And I only looked for English language. There must be much more to be found with some more effort.

[Edited on 30/12/2014 by Nicodem]


Yes I am sure you can find a lot of good information nicodem. When you have full access to the forum. There is no development crew section available for me, nor can I message members or make posts. I thought there were not hidden sections but it looks like there are.

I mistakenly thought that there was a procedure in the CTH thread here http://www.sciencemadness.org/talk/viewthread.php?tid=8929
where a nitrostyrene was reduced directly to an amine in a single step procedure. I must have seen a typo or made a mistake.

In regards to the concerns about the adaquate equipment, this is proving to be a concern. Regulators are priced at 300-500$ each here. Additional pressure gauges, tubing and clamps will probably see the whole setup come close to $1000. Finding regulators off ebay at a reduced price may work; if the threads on the h2 bottles available here will be suitable.

Since I do not stand to profit off what is synthesised, this is likely going to be a barrier to doing a pressurized hydrogenation. I will have to save up for a while.




Bert - 1-1-2015 at 00:24

Hydrogen embritrlement...

http://en.m.wikipedia.org/wiki/Hydrogen_embrittlement

morganbw - 1-1-2015 at 11:28

Quote: Originally posted by Bert  
Hydrogen embritrlement...

http://en.m.wikipedia.org/wiki/Hydrogen_embrittlement


That is very real. It was a potential, and sometimes real, problem in an electrochemical process I was involved with.

zed - 3-1-2015 at 14:51

"Yes I am sure you can find a lot of good information nicodem. When you have full access to the forum. There is no development crew section available for me, nor can I message members or make posts. I thought there were not hidden sections but it looks like there are."

Hidden sections? Must be hidden from me too.

More likely, we just have access to longer memories. Since many of us have pondered the current subject, for 10, 20, 30, or even 40 years......we've got a lot of invisible background information, bouncing around inside of our heads.

Cheer up! You are getting the friendly treatment.

Nicodem - 9-1-2015 at 12:49

Quote: Originally posted by Templar  
Yes I am sure you can find a lot of good information nicodem. When you have full access to the forum. There is no development crew section available for me, nor can I message members or make posts. I thought there were not hidden sections but it looks like there are.

You are talking a lot of nonsense, because it is so obvious to me that you did not check the posts I cited. They are obviously not in any hidden sections. Read my previous reply again. I did not list the ones that are not public.
Quote:
Since I do not stand to profit off what is synthesised, this is likely going to be a barrier to doing a pressurized hydrogenation. I will have to save up for a while.

You would profit more by learning the chemistry of whatever endeavour you are up to. There is a lot of experience published in the scientific literature that you could look up.
Why do you want to use pressure vessels where there is no need for it? You should first practice hydrogenations at atmospheric pressure. Without proper knowledge and experience, you are more likely to get injured or frustrated due to failures.

solo - 19-2-2016 at 14:41

Reference Information


Beta- Phenylehylamines: THE CATALYTIC HYOROGENATION OF OMEGA- Nitrostyrenes
0.P.Wagner,A. I.Rachlfn
Synthetic communications
1971,1:1, 47-50
doi.10.1080/00397917108081616




Abstract
Good yfelds o f s-phenethylamfne hydrochlorfde oalts are obtafned directly from the catalytic reductfon o f a,3-unsaturatd nitro compounds in dilute hydrochloric acid.

Attachment: php6BgBQP (454kB)
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clearly_not_atara - 19-2-2016 at 17:31

Quote:
To a suspension of X g of an w-nitrostyrene in X mL of conc. hydrochloric acid is added ca. 0.2-0.3g of 10% Pd-C catalyst and enough water to make the w-nitrostyrene comprise 5-7% of the mixture. Reduction is carried out at 50-80º under 500-1500 p.s.i. of hydrogen in an agitated autoclave.


(from the above paper)

solo - 19-2-2016 at 18:22

.....this may be more approachable with less pressure....solo



Synthesis of Phenethylamines
by Hydrogenation of beta-Nitrostyrenes

Kohno, Sasao and Murahashi
Bull. Chem. Soc. Jpn.
63(4), 1252-1254 (1990)

Attachment: Synthesis of Phenethylamines by Hydrogenation of beta-Nitrostyrenes.pdf (1.1MB)
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solo - 20-2-2016 at 07:08

Reference Information




Iron-catalysed, general and operationally simple formal hydrogenation using Fe(OTf)3 and NaBH4
Alistair J. MacNair,a Ming-Ming Tran,a
Org. Biomol. Chem.
2014, 12, 5082
DOI: 10.1039/c4ob00945b



Abstract
An operationally simple and environmentally benign formal hydrogenation protocol has been developed using highly abundant iron(iii) salts and an inexpensive, bench stable, stoichiometric reductant, NaBH4, in ethanol, under ambient conditions. This reaction has been applied to the reduction of terminal alkenes (22 examples, up to 95% yield) and nitro-groups (26 examples, up to 95% yield). Deuterium labelling studies indicate that this reaction proceeds via an ionic rather than radical mechanism.

[Edited on 20-2-2016 by solo]

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solo - 20-2-2016 at 10:05

.....and of course there is the psyloxy's Hive archive method without gas....solo

-----------------------------------------
psyloxy
(Hive Bee )
6/8/00 07:42 AM

Re: Nitropropene Reduction new [Post#: 15452 ]

What about NaBH4/Pd/C ? This seems to work without pressure and yields around 70%.

------------------------------------------------------------------------------------------
dreamer:


- 0.05mol 8gr beta nitropropene C9H9NO2 63gr/mol
- 13gr 5% Pd-C
- 100ml Methanol
- 50ml THF
- 0.15 mol NaBH4

- 8gr P2NP are dissolved in 50ml THF and 50ml Methanol and is stirred on
a magnetic stirrer
- 1.9gr NaBH4 are slowly added over a period of 30min
- the addition of nabh4 is effervscent
- after 15min of stirring 13gr 5% Pd/C in 100ml methanol is added;
- don't add the Pd/C without solvent, it will catch fire )
- the you should add slowly over a period off 1h (i did it) 4 gr NaBH4;
- reaction is continued for another 3h and 5ml of acetic acid is added
(to neutralize NaBH4 .. maybbe you don't this) and 20ml of 31% HCl and
50ml of H2O;
- the solution turns red
- Pd/c is filtered away and washed with Methanol and dH2O
- Methanol and THF is eliminated, the red color disappears
- all is washed with DCM
- make it basic with 100ml 25%NaOH and extract; you should get around 5gr
of the freebase (i did), yield ~70%; the salt is easily made with H2SO4
in ethanol, but don't add too much H2SO4 or your salt dissolves (if
this happens make all basic and extract)

a few days bevor i tried the same thing with ethanol, yields were much
lower and the addition of NaBH4 was not so effervescent
------------------------------------------------------------------------------------------

--psyloxy--
-----------------------------


.......that's a lot of palladium, for 8 gr....better recycle it , otherwise it's an expensive route.....solo

[Edited on 20-2-2016 by solo]

[Edited on 21-2-2016 by solo]

solo - 21-2-2016 at 09:35

......there is always the Hive's post, a cooperation of hive members and hyperlab members........solo

--------------------------------------------------


Reduction of Nitroalkenes with Aluminium Amalgam
Translation and Compilation by Antoncho

Attachment: Reduction of Nitroalkenes with Aluminium Amalgam - [www.rhodium.ws].pdf (141kB)
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[Edited on 21-2-2016 by solo]

clearly_not_atara - 22-2-2016 at 10:16

Aluminum and its variants are well-known as reductants for this substrate; using NaBH4/Pd/C is really the same thing as two step NaBH4 >> Pd/C/formate except you waste a lot more borohydride for not very much more yield. Unfortunately real advances here are quite rare.

Copper hydride complexes are known to reduce activated alkenes with good selectivity and might be able to replace borohydride in the nitroalkene >> nitroalkane transformation. Usually copper (I) t-butoxide is used as the precursor with a hydrogen donor to generate CuH in situ. Here's an example converting terminal nitroalkenes to nitroalkanes:

http://onlinelibrary.wiley.com/doi/10.1002/ange.200352175/fu...

In this case big chiral ligands are used to enforce chirality; there are simpler complexes of CuH including (CuH(PPh)3)6 also known as Stryker's reagent although we might prefer, for simple reasons, a complex without triphenylphosphine. N-heterocyclic carbenes have also been used as ligands although they can be somewhat difficult to prepare. 2-methoxyethanol, in the form of Red-Al, is one of the simplest complexing reagents I've seen:

http://pubs.acs.org/doi/abs/10.1021/jo01289a035

For at-home purposes it would be nice to find a ligand that doesn't use phosphorus and a reductant that doesn't use silicon or aluminium. Thiamine and H2 might work if you're lucky. It appears that a copper hydride can be generated from CuBr and LiHAl(OMe)3 and used to reduce unsaturated ketones to saturated ketones:

http://pubs.acs.org/doi/abs/10.1021/jo00439a015

[Edited on 22-2-2016 by clearly_not_atara]

solo - 22-2-2016 at 10:49

Reference Information



Catalytic Enantioselective Conjugate Reduction of b,b-Disubstituted Nitroalkenes
Prof. Dr. E. M. Carreira, C. Czekelius
Angew. Chem.
2003, 115, 4941 –4943
DOI: 10.1002/ange.200352175




Abstract
Optically active nitroalkanes are versatile precursors for a wide range of useful building blocks for fine-chemical syn- thesis. However, only a few effective methods for their preparation are available.[1–3] Despite recent advances in the addition of dialkyl zinc reagents to a,b-unsaturated nitro- olefins, the complementary method involving metal-catalyzed enantioselective reduction of b,b-disubstituted nitroalkenes has not been reported.[2] Herein we document such an approach in which bisphosphane–Cu complexes (with tol- binap or josiphos[4]) catalyze the enantioselective reduction of b,b-disubstituted nitroalkenes, giving optically active b,b- disubstituted nitroalkanes in useful yields and selectivities




-------------------------------



Reduction of a,@-UnsaturatedNitriles with a Copper Hydride Complex
Morey E. Osborn, James F. Pegues
J. Org. Chem.
1980,45, 168-169


Introduction
The reduction of conjugated nitriles to their saturated counterparts has long been a vexatious synthetic problem because of oft-encountered overreduction to the amine,* hydrodimeri~ationd,~ecyanation; and/or polymeri~ation.~ Recently, Profitt, Watt, and Corey published results achieved with magnesium metal in methanol.6 Not only did reductions performed with this reagent proceed readily and in high yield but compatibility with a variety of other functional groups was also demonstrated.............



--------------------------------------------




Reductions of conjugated carbonyl compounds with copper hydride - preparative and mechanistic aspects
M. F. Semmelhack, R. D. Stauffer, A. Yamashita
J. Org. Chem.
1977, 42 (19), pp 3180–3188
DOI: 10.1021/jo00439a015



Abstract
The reaction of lithium trimethoxyaluminum hydride with 0.5 molar equiv of cuprous bromide produces a heter- ogeneous mixture referred to as the Licomplex, while sodiumbis(2-methoxyethoxy)aluminumhydride with 1.0 molar equiv of cuprous bromide gives a similar mixture, the N a complex. B o t h reagents are effective in selective reduction of the olefin unit in conjugated ketones and esters, including two examples of acetylenic esters. The Li c o m p l e x i s m o r e e f f i c i e n t w i t h c y c l o h e x e n o n e s , w h i l e t h e N a c o m p l e x g i v e s b e t t e r y i e l d s i n r e d u c t i o n of a c y c l i c e n - onesandenoates, especially inthepresenceof2-butanol. Deuteriumlabelingexperiments showthat thehydrogen which is transferred to the Pposition of the conjugated carbonyl compound originates from the hydridocuprate re- agent; the 2-butanol appears to serve as a weak acid, inhibiting polymerization. Inthe absence of 2-butanol, reduc- tion of methyl cinnamate produces dimethyl meso-3,4-diphenyladipateas a major product, apparently the result of radical anion intermediates. Aldehyde, ketone, and halide functionality are reduced at rates comparable to the rate of enone reduction, but nitrile and ester units are inert.

Attachment: Catalytic Enantioselective Conjugate Reduction of b,b-Disubstituted Nitroalkenes.pdf (155kB)
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Attachment: Reduction of a,@-UnsaturatedNitriles with a Copper Hydride Complex.pdf (267kB)
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