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Topic: From an aldehyde to a nitrile  (Read 812 times)

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Offline Juaqui

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From an aldehyde to a nitrile
« on: June 12, 2019, 04:37:24 PM »
Hello!

I'm not understanding a mechanism. I have this reaction:
https://ibb.co/dbBKQW0

I think  the hydroxylamine hydrochloride is for forming the oxyme and the formic acid is the solvent, but which is the role of the sodium formate?

Thank you!

Offline sharbeldam

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Re: From an aldehyde to a nitrile
« Reply #1 on: June 12, 2019, 05:58:37 PM »
If i'm not wrong, this should be reductive amination and then the oxime gets converted to nitrile via beckman rearrangement.

full mechanism: https://www.masterorganicchemistry.com/reaction-guide/beckmann-rearrangement/

Offline Babcock_Hall

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Re: From an aldehyde to a nitrile
« Reply #2 on: June 12, 2019, 07:34:17 PM »
@OP, When a weak acid and its conjugate base are present in comparable amounts, what do you have?

Offline Juaqui

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Re: From an aldehyde to a nitrile
« Reply #3 on: June 13, 2019, 12:57:01 PM »
@OP, When a weak acid and its conjugate base are present in comparable amounts, what do you have?
You have a buffer, but how is the formation of the nitrile then?

Offline rolnor

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Re: From an aldehyde to a nitrile
« Reply #4 on: June 13, 2019, 01:29:01 PM »
You have a double-bond and want a triple-bond, what reaction can do that?

Offline Babcock_Hall

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Re: From an aldehyde to a nitrile
« Reply #5 on: June 13, 2019, 02:03:31 PM »
@OP, When a weak acid and its conjugate base are present in comparable amounts, what do you have?
You have a buffer, but how is the formation of the nitrile then?
My memory may be off, but I seem to recall that the rate of similar reactions is maximal at slightly acidic pH.  I will try to double-check my memory on this as soon as I can.

Offline AWK

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Re: From an aldehyde to a nitrile
« Reply #6 on: June 13, 2019, 02:45:16 PM »
Sodium formate removes HCl and increases the boiling temperature of the reaction mixture. Removing of HCl prevents the Beckman rearrangement and allows the thermal decomposition of oxime formate with good yield.
AWK

Offline hollytara

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Re: From an aldehyde to a nitrile
« Reply #7 on: June 13, 2019, 08:51:19 PM »
Oxime eliminates water to give triple bond.  Acids (HCl, Formic acid) catalyze the protonation of the OH, while the base (sodium formate) takes the H+. 

Offline Juaqui

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Re: From an aldehyde to a nitrile
« Reply #8 on: June 16, 2019, 12:00:06 PM »
Thank you, people!

Offline Juaqui

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Re: From an aldehyde to a nitrile
« Reply #9 on: June 16, 2019, 08:38:18 PM »
And why not acetic acid and sodium acetate?  ???
Could it be because of the more negative density of the oxygen in the formic acid, necessarily for substrating the H bonded to the N at the end?

Offline AWK

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Re: From an aldehyde to a nitrile
« Reply #10 on: June 17, 2019, 12:55:30 AM »
Such a method is also used but with the addition of acetic anhydride.
AWK

Offline Juaqui

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Re: From an aldehyde to a nitrile
« Reply #11 on: June 17, 2019, 07:27:57 AM »
In other words, is kind of Wohl degradation, isn't it?

Offline AWK

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Re: From an aldehyde to a nitrile
« Reply #12 on: June 17, 2019, 12:03:23 PM »
Not exactly. Alfred Wohl used this reaction in 1893 for the conversion of glucose oxime to nitrile. He isolated oxime and tested its geometry. He knew that only syn-oximes react with acetic anhydride with the formation of nitrile. Next step reaction with sodium ethoxide was a real degradation with carbon chain shortening.
AWK

Offline wildfyr

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Re: From an aldehyde to a nitrile
« Reply #13 on: June 17, 2019, 01:17:39 PM »
Whenever I see descriptions of synthesis in the late 1800s I am so impressed at their ability to deduce structure.

Offline Juaqui

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Re: From an aldehyde to a nitrile
« Reply #14 on: June 17, 2019, 01:47:56 PM »
Not exactly. Alfred Wohl used this reaction in 1893 for the conversion of glucose oxime to nitrile. He isolated oxime and tested its geometry. He knew that only syn-oximes react with acetic anhydride with the formation of nitrile. Next step reaction with sodium ethoxide was a real degradation with carbon chain shortening.

And what is the way in which formiate removes HCl to increase the boilling point of the mixture?

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