[crt]

Hi,

I would need some hydrogen scavenger for my dehydrogenation experiments. I already tried neohexene, norbornadiene and acetophenone but would be curious if there are other molecules which readily accept hydrogens. Reaction conditions are 60-150C and atmospheric or slightly elevated pressure. Under these conditions the hydrogen scavenger should be either in gas or liquid phase, the latter one would be better but it is not a must. It can be polar on apolar.

It would be also interesting to know if there is any inorganic molecule/metal which absorbs/reacts with hydrogen.

Thank you.

[cundi]

I'd try some simple molecule with a benzyl or Cbz group. (MeNH-Bn, or Cbzcarbamate,...)
In anycase, you'll need Pd/C (or other catalyst) in order to activate the hydrogen.

I hope it could be useful for you.

[crt]

Hey, thanks cundi. This MeNH-Bn... which moiety catches hydrogen? Why is the Bn group important?
The catalyst should not be a problem, however.

[cundi]

Bn-N bonds are easily hydrogenated.
Bn and Cbz are protecting groups for amines. Take a glance at this web:
http://www.organic-chemistry.org/protectivegroups/#Amino
The deprotection is, commonly, carried out via hydrogenation.

Good luck, and please let me know if it works.

[OC pro]

Cyclohexene is a common hydrogen scavenger used in dehydrogenation reactions (mostly in the presence of Pd/C).

[cundi]

It's right, cyclohexene is commonly used. But an excess of it can generated H2 (and benzene) if it is employed at high temperatures.

[OC pro]

Dehydrogenation of cyclohexane to benzen will certainly not happen at 150°C. It will occur at above 250°C in the presence of nickel catalysts.
Therefore, an excess of cyclohexene ist not a problem in this case.

[cundi]

I don't know which is the reaction thof crt, and really I don't know if cyclohexene would be a problem or not.
But I assure you that I had performed hydrogenation reactions at 90º - 100ºC using cyclohexene as hydrogen promoter.

Anycase , It a pleasure to deal with somebody that kwows what is talking about.

[crt]

Hey guys, thanks for the comments. I will give cyclohexene a try and we will see. However, I have to synthesize some more cat first, because I ran out of it

cundi: was cyclohexene a hydrogen source or acceptor? Or did you activate your catalyst with it?

[cundi]

Cyclohexene: colud be both things.
It has a double bond which can be hydrogenated but with heat it can liberated hydrogentaion and became benzene.
Depends on the conditions.

[crt]

I mean for what did you use it at 100C. The term "hydrogen promoter" was unclear.

[crt]

But I assure you that I had performed hydrogenation reactions at 90º - 100ºC using cyclohexene as hydrogen promoter.

Do you have maybe some reference?

[cundi]

http://www.erowid.org/archive/rhodium/pdf/cth.review.pdf

Take a glance.

I can't talk you about the proceess I did because is confidential information of a company, but I had hydrogenated a double bond with cyclohexene at 100ºC.

[crt]

Thank you. It is more than enough.