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Ortho-nitration of benzaldehyde

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rolnor:
interestingely the mention the ozonolysis of o-dinitrostilbene, I made that in -84. They get a little more if the o-isomer but even with there method they get mainly the m-isomer when doing direct nitration. To go via the dioxolane is not very impressive, more steps.

willijung1:
Maybe it has to do with the concentration of HNO3.
After reading more research papers on the matter, I learned that fuming nitric acid could catalyze nitration for various aromatic compounds in dcm (but also have a danger of detonation in dcm). Apparently they made fuming nitric acid in situ by protonating the NO3- ion, and the protonated form then separated from the aqueous layer into the dcm layer.
When I first read the procedure, I thought of 'concentrated nitric acid' as the 68% one present in my school lab. But now as I think again about it, they might have meant fuming nitric acid. Since 68% nitric acid is an azeotrope with water, the species mostly exists as NO3- ions which definitely wouldn't do the job.
Now somehow I'll try and find a less dangerous step which involves the in situ generation of the protonated form. (I well know that fuming nitric acid is extremely dangerous...)

Many thanks to those who gave me advice!

willijung1:

--- Quote from: rolnor on February 23, 2020, 10:36:43 AM ---Have you done a thorough litterature-search on this matter?

--- End quote ---

Maybe highly concentrated nitric acid might do the job...!
Have you ever tried making HNO3 in situ by mixing KNO3 or any other nitrate with sulfuric acid and then adding some dichloromethane? Several papers show this procedure for producing the designated nitrating mixture which results in ortho-nitration due to something called the 'chaperone effect.'

I'm slightly worried about this procedure because I have learned that nitric acid can detonate when mixed with organic solvents. Is there a difference between directly mixing nitric acid and an organic solvent and letting the protonated form separate into the organic layer..? Would it be safe enough to try out..?

rolnor:
You should be aware that people has worked with this problem for a very long time. That does not mean that its hopeless but very difficult to get the o-nitration. I think you need something new, to generate HNO3 this way will not fix the problem I think.

willijung1:

--- Quote from: rolnor on February 26, 2020, 03:58:21 AM ---You should be aware that people has worked with this problem for a very long time. That does not mean that its hopeless but very difficult to get the o-nitration. I think you need something new, to generate HNO3 this way will not fix the problem I think.

--- End quote ---

I'll definitely keep that in mind. Thanks!!

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