I am reducing the -CN group（with an α-NHBoc） to a primary amine with Hydrogen & Pd/C in MeOH. However after 24hs' reaction, it gives largely "dimmer-like" byproduct, namely secondary amine. There are scattering suggestions saying that addition of NH3H2O or acid would help to alleviate the side-reaction. Is there any review or detailed explanation on this subject?
Thanks for reading my question.
This is a very common transformation (i.e., the reduction of a cyano group to a primary amine, while sparing the reduction of a boc-procted amine). I just checked scifinder and there are 73,172 reports of this transformation being successful.
For example, here is a report that used LiAH for the reduction of the CN group, without deprotection of the boc group in excellent yield (92%).
Grigorenko, Tetrahedron, 63(10), 2257-2262; 2007
If you can provide the structure of your compound and reaction conditions and any findings (e.g., TLC, NMR, etc.) it would be easier to determine what is going wrong and hence help you get around this.
Many thanks to all the answers! And special thanks to Grant Simpson for detailed description.
Later I found that there were several reviews discussing factors that influence the hydrogenation of cyano with metal catalyst.
I. Adv. Synth. Catal. 2002, 344, 1037 - 1057
II. 10.1002/adsc.201400940
As to my case, Raney Ni with 5% ammonia in MeOH worked well in my substrate.
However, by addition of ammonia in Pd/C is useless, which has been proved by earlier reports.
Hope this will help others facing with similar problems.
Another thing to note: RaNi with ammonia has a tendency to leach Ni into the product. This may sometimes be apparent by extra color.
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