[dfodor]

Hi,

I would need some help in sample preparation of hydrogenation reactions.
I am working in autoclave with an organic substance and water solvent. After taking the sample I extract the product in DCM (1:1 volume) and inject in GC. My problem is that the deviation of the results are quite great and I do not know why, I do everything exactly the same way.

Can the extraction cause great deviations? (I measure the weights and correct the values with the volume ratio)
Is it generally a problem to make hydrogenations in water? (somebody told me, but I see no reason)

Thank you

Daniel

[stewie griffin]

Well based off of the info given I can't say if water is a bad solvent of not (what are you trying to hydrogenate, what catalyst, etc?). Anyway, for the hydrogenations that I've done using Pd/C of Pd(OH)₂, I run them in ethyl acetate, though methanol or ethanol are also used by others.

[Med90]

you can do the hydrogenation in solvent mixture containing H2O. (THF: MeOH:H2O= 20:1:1, just an example). Mostly ethylacetate is preferred.
For setup, plz check out this video <a href="http://www.youtube.com/watch?v=vg3HYGvVbSo">Hydrogenation demonstration</a>

[Dan]

Water should be fine. I've done azide reductions, reductive aminations and benzyl hydrogenolyses in water, ethanol, ethanol/water mix, methanol, 1,4-dioxane, 1,4-dioxane/water mix, THF and ethyl acetate under H₂ with 10% Pd/C. All work for those purposes (though I find ethyl acetate a bit slow).

What sort of hydrogenation are you doing, alkene -> alkane? Also, can you be more specific about the deviations?

[bromidewind]

I agree with the previous replies about hydrogenation. Assuming that this is an alkene to an alkane, then water is a fine solvent. It is quite protic, which is necessary for a reaction such as this. As previously mentioned, methanol and ethanol are good as well. As for the deviations in your GC, what settings are you using? Perhaps your sample is moving through the column too slowly. The NIST Chemistry Webbook (http://webbook.nist.gov/chemistry/) has a great search engine for comparing GCs, complete with settings from various researchers.

[dfodor]

Hi guys,

thank you for your replies. The problem is apparently solved. I hydrogenate levulinic acid the product is gamma-valerolactone. I measured the conversion after 1 hr reaction time but got always different values. My guess is that the dissolution of levulinic acid was not complete, water was fine indeed. I use Ru/C by the way at 150C and 50bar in 50mL autoclave.

There is another problem, however. As water is mainly steam and levulinic acid is mainly in liquid phase, I could not solve the sampling and decided to make the reaction in neat levulinic acid to measure kinetics. The problem is that by doing this I measure only pseudo order kinetics for hydrogen but I do not know the hydrogen concentration under these conditions. Is there any way to estimate its concentration in levulinic acid?

cheers

Daniel