Problem with amine purification

[Acetoby]

Hi,

 

I'm currently dealing with amine synthesis and since I'm new on this field I also don't have much experience on the purification. Here's my problem:

I tried an unusual method to convert a benzylic nitrile to the corresponding amine. It involves DIBAL-H, NH4Br and NaCNBH3. I can't use LiAlH4 or H2 to reduce the nitrile as it would mess up other functionalities in the molecule.

After acid base extraction the TLC (silica, EE/MeOH, 10:1, 5% TEA) of the crude product showed several spots whereas only one of them was blue/purple (ninhydrin). The other ones were somewhat brown or yellow... After column chromatography (same system as above) I was able to isolate all spots I saw on the TLC plate except for one: the blue amine spot, which I think is my desired product.

 

So does anyone know what's going on? Hope you can help me...

 

Besides: Rf value of the blue spot was ~0.35 and there were two spots below that one which I isolated as well. And I didn't pretreat the silica with TEA...

[Fuzzwood]

The last part might have been the problem. Either TEA sticks to the silica, or your product does. If you still have the column or at least the silica, you could try to get your product off by flushing it with methanol.

[Acetoby]

I packed the column with the solvent system I mentioned. Thought that would do it.

After finding out that no amine eluted from the column I flushed it with EE/MeOH 5:1, 10% TEA. Still nothing eluted...

[hypervalent_iodine]

If you flush with straight MeOH, it may come off (but it will come off with other things).

 

I agree with Fuzzwood though, your problem is likely that you didn't pretreat. Also, you really don't need that much TEA. When I've done it in the past, I've pretreated with 5% TEA and then eluted with 1-2%.

Also, did you pretreat your TLC plates?