[qw098]

Hi guys,

In the lab the other day I hydrogenated  methyl 3-nitrobenzoate into methyl 3-aminobenzoate.

I was wondering:What do you guys consider a good percent yield for such a reaction or an average percent yield.

I was told catalytic hydrogenation should yield very high yields (Close to 100). Is this true?

Thanks!

[fledarmus]

Yes, especially with such an easily reduced group on a molecule with no other reactive groups. If you are having trouble getting a good yield with this sort of reaction, the only thing I could suggest would be to make sure that your product is soluble and you aren't filtering it out with your catalyst.

[qw098]

Thanks Fledarmus.

I got a percent yield of 89% so I am pretty happy with that. Our lab instructor filtered our catalyst out with Celite so I will have to poke fun at him next time I see him and let him know one of the reasons I didn't get a 100% yield was because of him

The balanced reaction was C6H5NO2 + 3H2 ==> C6H5NH2 + 2H2O. For this reaction we used Pd/C as a catalyst... and as an organic solvent we used methanol. I was wondering if the methanol needed to be anhydrous for this reaction to proceed. I was thinking... anhydrous methanol is methanol that doesn't have water... therefore if we had methanol that did contain some water... the equilibrium would shift to reactants based on Le Chatelier's Principle.

Is my above rationale correct or am I completely wrong, and the methanol doesn't need to be anhydrous for this reaction to proceed.

Thanks!

[orgopete]

I don't know the equilibrium constant for the reduction, but I think it significantly favors the reduction. Water will not interfere with the reduction, so you are safe in that regard and it is a by-product of the reduction.

While my inclination was to reject le Chatelier's Principle in this example, I think the reaction could be reversible. Carbon monoxide and hydrogen can be produced from methane and water, see http://en.wikipedia.org/wiki/Syngas. Since the reduction is exothermic, you would have to heat the reaction to drive it backwards. I will guess it would take a serious amount of heat also.

[Doc Oc]

I've always gotten very good yields on this reaction too.  After you filtered, did you rinse out the reaction flask as well as the Celite with more methanol?  Your situation in particular would probably benefit, since free amines are very sticky.

Dry methanol is not necessary, I've used methanol from a wash bottle and gotten excellent yields.