Sciencemadness Discussion Board

Carboxylic acid to nitriles using microwave radiation

Opylation - 10-9-2019 at 21:32

Hey guys,

I came across an amazing synth that uses commercial microwaves, hydroxylamine, zinc, and PEG400 to convert aromatic carboxylic acids to nitriles at a yield of upper 90%. Just thought I’d post it because it seems easy as cake

Attachment: cao2010.pdf (60kB)
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[Edited on 11-9-2019 by Opylation]

[Edited on 11-9-2019 by Opylation]

Ubya - 10-9-2019 at 23:51

well this is very exciting, if someone has hydroxylamine he should definitely try this out and report the results. finding the right power setting seems the only variable to find for each molecule to test

draculic acid69 - 11-9-2019 at 00:56

Peg400 is what they put in pills to stop ppl extracting the stuff in them? If it is good luck getting rxn products out of the slimy soup you'll end up with.

Ubya - 11-9-2019 at 01:05

PEG400 has a big affinity for water, so extracting the nitrile with an apolar solvent (DCM was used in the paper) should be the way to go, but i've never worked with it, someone that had can enlighten us a bit more

[Edited on 11-9-2019 by Ubya]

happyfooddance - 11-9-2019 at 01:28

I doubt any emulsification agent or even PTC would hinder a simple steam distillation of this product, correct me if I'm wrong.

From a mechanics standpoint, a steam distillation should work fine as a first step for a work up.

Boffis - 11-9-2019 at 08:38

Do I understand the paper correctly? It states that 5% PEG is required but 5% of what? It appears to be essentially a solvent free reaction so that the 5% must presumably be 5% of the mass of other reactants? Mmmm who's got a microwave they are prepared to sacrifice? And how do you measure the power output?

I was also under the impression that dpomestic microwave ovens had a microwave generator that pumps out a constant output and that the overal power output was controlled by the time the microwave generator was switched on or off?

Cactuar - 11-9-2019 at 09:29

Quote: Originally posted by Boffis  
Do I understand the paper correctly? It states that 5% PEG is required but 5% of what? It appears to be essentially a solvent free reaction so that the 5% must presumably be 5% of the mass of other reactants? Mmmm who's got a microwave they are prepared to sacrifice? And how do you measure the power output?


5 mol%. It even says so on the first page.
Quote: Originally posted by Boffis  
I was also under the impression that dpomestic microwave ovens had a microwave generator that pumps out a constant output and that the overal power output was controlled by the time the microwave generator was switched on or off?


This is my understanding as well.

Boffis - 11-9-2019 at 10:47

@Cactaur, I think you missed the point of my first comment. This is essentially a solvent few reaction since 5% PEG in the example given for benzoic acid is only a little over 0.3g say 0.3ml. This will barely make the mixture moist. The zinc particles are conductive so will they not get thunderingly hot? I just find the report "iffy". I would like to hear someone from SM try this and see what their results are but the lack of information on mixing, grinding together to get a homogeneous fine mixture, the addition of the PEG the nature of the reaction vesicle etc is poor. I think you will find it very difficult to reproduce these results. If you contact the authors and say "I can't reproduce your results" they will respond saying you didn't follow the procedure accurately but given the lack of detail its hardly surprising.

Anyway, I remain to be convinces about those yields.

icelake - 11-9-2019 at 11:03

Quote: Originally posted by Boffis  
This is essentially a solvent few reaction since 5% PEG in the example given for benzoic acid is only a little over 0.3g say 0.3ml.


I think 5 mol% means 50 mmol -- 50 * 400/1000 = 20 g - more realitic?

5 mol% in theory:

x / (65+x) = 0.05 -> x = 3.421 mmol = 1.368 g.

[Edited on 11-9-2019 by icelake]

wg48temp9 - 11-9-2019 at 11:42

231W for 20 minutes is a lot of power to be absorbed by about 8g of reactant.

Its 177,000J about 221,000 J per g. It would vaporize 8g water and then some. It would melt many ceramic materials.

In a different microwave synthesis using a few grams of reactants used 1kW for 30 minutes.

I guess only a small fraction if the input power is dissipated in the reactants as its dependent on the absorption characteristics of the reactants and characteristics of the microwave oven. Which probably means some experimentation with the time and power level will be required.



Cactuar - 11-9-2019 at 14:19

Quote: Originally posted by Boffis  
@Cactaur, I think you missed the point of my first comment. This is essentially a solvent few reaction since 5% PEG in the example given for benzoic acid is only a little over 0.3g say 0.3ml. This will barely make the mixture moist. The zinc particles are conductive so will they not get thunderingly hot? I just find the report "iffy". I would like to hear someone from SM try this and see what their results are but the lack of information on mixing, grinding together to get a homogeneous fine mixture, the addition of the PEG the nature of the reaction vesicle etc is poor. I think you will find it very difficult to reproduce these results. If you contact the authors and say "I can't reproduce your results" they will respond saying you didn't follow the procedure accurately but given the lack of detail its hardly surprising.

Anyway, I remain to be convinces about those yields.


Yes, that is how I believe it was done. Mixed up to a paste and nuked. They even refer to it as a catalyst which is probably why they give the amount in loading.

You are making a good point about the zinc particles. The microwave they claim to have used was this Midea.