anyone experienced with Urushibara?

[starlight]

Hi,

Somebody that I don't know ran an Urushibara on TMP2NP.

Highly active product was isolated in the form of a clean, white powder. This was exciting because it was the first success of its kind for this person.

However, the reduction did not run to plan and the yeilds experienced were appalling (250mg final product from 7g TMP2NP).

The writeup followed was that of Antibody on Rhodium's page.

The problems were as follows:

In the preparation of the catalyst, it was impossible to add 35g of Aluminium foil, as the mixture was almost solid after around 20g.

12g of the catalyst were digested as detailed.

The catalyst was washed and suspended in ETOH. The nitropropene was added and the addition of Aluminium and HCL was begun.

No bubbles of hydrogen were experienced and the Aluminium did not dissolve after the first addition of Al (1g) / HCL (3ml). Ditto after the second addition. Warming the mixture to 55C did not initiate the reaction. After one hour there was still no discernible reaction.

Becuase there were problems in initiating the reaction, more HCL was added (maybe another 6ml to give a total of 12ml). This caused a green colouration to the solution (Local concentration of HCL in the Mixture must have got at the Nickel catalyst). Immediately the Aluminium began to react and things proceeded more or less as expected for the rest of the addition of AL/HCL (except that the mixture kept having to be warmed back to 55C in order to get a reasonable rate of Al dissolution / bubble formation).

After basification of the reaction there was a smell of ammonia (which disappeared on stripping the EtOH from the alcoholic reacation overhead)

Questions are as follows:

Has anone else followed the catalyst preparation instructions and had the same problems with adding all of the Al?

Why did the Al fail to react?

Was the attack of HCl on the Nickel catalyst responsible for the appalling yields?

Is it normal to have to keep warming an Urushibara?

Why the smell of ammonia?

Does partial reduction of Nitro compounds and side reactions lead to nasty carcinogenic products at all?

many thanks.

./

[SPISSHAK]

urushibara sounds promising but you did'nt mention how it was prepared.
a little bird tells me that urushibara that is activated with a base is the most active.
maybee the catalyst was your problem.
have you perfected this since then?

[starlight]

Sorry to say I gave up and started using easier/more reliable reducing agents.

[Daphuk_up]

SWID has also tried Urushibara many times.  He has tried both U-Al-A and U-Zn-B.  He has tried each of these at least four times with 2,4,5-TMPNP.  In every single case, he was unable to isolate a yield.  SWID isn't the most expierenced Bee by far, but when trying to reduce 10g at a time, he should be able to isolate something, even if yields were only 10%.  Seeing as how he has now wasted ~50g of nitropropene, he is looking for one of those above mentioned "easier more reliable" methods.

[SPISSHAK]

does not reveal too much detail.
I did notice this
"Subsequent work-up showed quite a bit of unreacted material, but a fair bit ended up in the water layer after acidification.  Unfortunately, SWID (as he is so prone to do) did something stupid, and used chloroform as his non-polar solvent.  Wasn't a problem for the acidification, but when basifying, chloroform is no good.  He titrated his water solution with the intent of causing the TMA to oil out, but instead he got a bizarre brown precipitate."
Chloroform fcorms dichlorcarbenes on treatment with bases.
also, tma is difficult to crystalize using hydrogen chloride gas.
another caveat is that you mentioned you dried using CaCl2
I read this is a nono for amines as they tend to complex wtih Calcium Chloride (correct me if I'm wrong)

[Antibody2]

it was impossible to add 35g of Aluminium foil, as the mixture was almost solid after around 20g. as Ab2 recalls the viscosity of the rxn is abit of a problem. It has been a few years since this rxn was run but if memory serves about 1/2  to 3/4 through the precipitation of Ni you need to add all the remaining Al foil at once, otherwise as you have noted it becomes too viscous to allow addition. The trouble with this is that some Al is unreacted at the end and neeeds to be removed afterwards (no big deal). The solution to this problem would be to use Al dust/powder that could all be added at once. This would also have the effect of ensuring a uniform precipitation rate (and a more uniform catalyst activity as the rate of precipitation affects the partical size and thus the activity of the resulting catalyst)

Has anone else followed the catalyst preparation instructions and had the same problems with adding all of the Al? see above

Why did the Al fail to react? this makes no sense

  Was the attack of HCl on the Nickel catalyst responsible for the appalling yields? In Hata's book "New Hydrogenation Catalysts" he clearly states that that any nickel ion remaining in solution (green coloration) will drastically reduce the activity of the catalyst. The green color indicates you have made NiCl2 out of your catalyst. This is why it is crucial that Al be added before the HCl, so that it will react with the Al and not with the Ni (which takes longer much to react)
Is it normal to have to keep warming an Urushibara? no, not at all, in fact at some points the hydrogen generation was so vigourous the stirring had to be stopped to prevent rxn vessel from overflowing

  Why the smell of ammonia? that is a very good question, there shouldn't be. I wonder if you solvent wasn't contaminated with something that reacted with your HCl before it reacted with Al and might also be responsible for the ammonia smell. the only odour you should get is volatized ethanol with maybe a whiff of HCl

Does partial reduction of Nitro compounds and side reactions lead to nasty carcinogenic products at all? when in doubt about your product test the MP, but i expect that partial redxns would result in the oxime being formed whiich wouldn't form an HCl salt

[Daphuk_up]

SWID is amazed.  You just revealed more about what he has been doing wrong in one paragraph than he has been able to figure in the month or two since his last attempt.

In previous attempts, he was bright enough not to use chloroform as his non-polar solvent.  Unfortunatly, as near as he can remember, he HAS been using CaCl2 as his drying agent.  SWID had no idea that it might form a complex with amines.

Also, in almost every write-up on rhodiums page, the TMA-2 is crashed out of toluene using either direct gassing or pre-gassed toluene.  If you cant crash this stuff with HCl, what can you use?  Sulfuric?

Not be contrary or anal, but SWID would hardly call what he wrote a 'write up'.  More like a regurgitation from memory after a lot of work that resulted in failure and frustration.  SWID is only now, several years after beginning this hobby, gotten into the habit of taking notes so that the experiment may be relayed to others in a concise manner.  Ironically, a few months ago, he would have called it a 'write-up'.

Looking back at that thread, SWID never returned to mentioned that HCl will preferentially eat up U-Zn-B(s) over aluminum, resulting very shortly in no catalyst and a lot of solvated ions.

SWID also forgot to mention he tried the U-Al-A write-up from Rhodiums page, followed it to the letter, and ended up with yet another flask filled with a sky-blue polymerized crap.  But, again, he used CaCl2 as his drying agent in all steps.  And toluene pre-gassed with HCl.

It was at this point that he decided to seek out a new method.  The Urushibara looks great on paper, and even has at least one claim from an Senior Bee that it works.  SWID could just never make it happen though.