July 18, 2019, 07:19:28 AM
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Topic: Red-Al reduction of nitrile to amine?  (Read 853 times)

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Offline Reddart

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Red-Al reduction of nitrile to amine?
« on: March 06, 2019, 03:41:57 PM »
Wiki says "yes"

Organic-chemistry.org says "No" (goes to aldehyde).

What say you?

Offline phth

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Re: Red-Al reduction of nitrile to amine?
« Reply #1 on: March 07, 2019, 01:46:15 AM »
Under what conditions? I have seen some examples of alkoxy aluminum dihydrides reducing things to aldehydes, but typically those procedures use low temps e.g. -78º taking advantage of the increased solubility. I think that more forcing conditions should work besides the reactivity of the hydrides being lowered due to the alkoxy ligands.

Offline Reddart

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Re: Red-Al reduction of nitrile to amine?
« Reply #2 on: March 07, 2019, 02:31:34 PM »
OK, that sounds good. I'll find out soon enough when my Red-Al comes in.

Offline wildfyr

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Re: Red-Al reduction of nitrile to amine?
« Reply #3 on: March 07, 2019, 04:05:37 PM »
Aldehydes are a delicate beast when it comes to reductions, my money would be on the ability to reduce it all the way if you kick it in the pants a bit with heat/equivalencies.

Offline rolnor

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Re: Red-Al reduction of nitrile to amine?
« Reply #4 on: March 09, 2019, 09:00:55 AM »
If you want aldehyde I think DIBAL/-78°C is a good reagent, with NaBH4/NiCl/MeOH you get the amine.

Offline Reddart

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Re: Red-Al reduction of nitrile to amine?
« Reply #5 on: March 26, 2019, 06:29:28 PM »
I haven't tried the nitrile yet, but I tried Red-Al on a amide-->amine reduction I have successfully done before with LAH.

While the reaction was beautifully clear, the workup wasn't as smooth as was the case with LAH.

 With LAH, after refluxing overnight, I cooled to RT, added Glauber's salt-celite (my go to workup in general for LAH reductions), some DCM, filtered and rinsed with DCM, and pumped off the solvents. It gave me high purity crystalline material that could be used without further purification.

With the Red-Al reaction, after adding the Glauber's salt and stirring for an hour, the filtration was very slow (some gel,  Al salts I presume) and the filtrate was cloudy, as if some of the salts went through the filter. I still need to pump off the volitiles on this reaction and check the purity by NMR.

I wonder if the ligand alcohols that render Red-Al soluble are causing these problems for the workup?

Anyone here who does the Glauber salt workups have any experience with Red-Al?

Offline Reddart

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Re: Red-Al reduction of nitrile to amine?
« Reply #6 on: March 30, 2019, 01:43:12 AM »
I can confirm that the Glauber's salt workup does not work well with Red-Al. I recovered more Al salts than product.

It is an interesting inverse of reaction properties: the LAH reduction is a cloudy suspension, but gives a crystal clear solution and nearly quantitative product after quenching with the salt/celite and filtering it, while the Red-Al reaction is crystal clear, but the product was a murky mess after quenching with the salt/celite and filtering it.

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