Sciencemadness Discussion Board

Reduction of 4-Chloro-3-nitrotoluene failure

aab18011 - 27-4-2022 at 23:19

Hey, looking for some help with my lack of success in reducing an aromatic nitro group.

I have tried multiple methods of reduction, much of which could be do to my own issues, but not due to reagent grade/purity.

Compound : 4-Chloro-3-nitrotoluene

I have tried the following:
-Zn/NaOH in hopes to get a diazo, which it does turn red, but so much leftover reactant after 24hrs of reflux. And my glassware is being eaten, so no more of that.
-Zn/HCl turns it into a green oil, of which is super hard to separate (still trying to fractionate it)
-Sn/HCl has given me so much trouble, and does not produce enough product, to the point I couldnt even collect a small sample.
-SnCl2/HCl which worked sort of, but my flask decided to yeet itself off my bench, which somehow I got the tiniest sample of super impure (zincate impurity) product. Deep red. But took literally 2 days.
-NaBH4/Carbon to zero avail. I even have some methanol in there, but nothing
-NaBH4/Zn/MeOH, nada
And I wish I had some nice hydrides, but I am not equiped to handle them yet.

NaBH4/Charcoal - DOI: 10.1080/00397910600764709
"NaBH4/Charcoal: A new synthetic method for mild and convenient reduction of nitroarenes" - Behzaf Zeynizadeh, Davood Setamidedeh

Also found a weird one with Zn/AcOH in THF from 0C to 20C range, but no data to back it up. Quite curious.

So i was wondering why Aniline reacts so well and so quickly, yet mine does not. Is it because of the chloro group? Or the methyl group? Id think the methyl group has zero effect, but I could see the halogen causing some weird chemistry since they are directly next to one another. Is the zinc/tin ripping off the chlorine like a lewis acid like AlCl3 can? Is oxygen getting in the way of the reaction?

If so, what is a better method besides the fancy toys like LiAlH4 and such?

16511302941355878496037930792606.jpg - 3.2MB

Edit - in case you are wondering why I dislike the time it takes to reflux is that my water circulator gets super hot and ends up heating the water in the condenser after a while. This becomes dangerous to do when I have to go to work or classes, or study. So its not a matter of laziness, but truly a lack of time and equipment. Now if only I had a chiller....

[Edited on 4-28-2022 by aab18011]

Boffis - 28-4-2022 at 01:09

Have you tried the age old and trusted iron fillings and a little HCl followed by steam distillation. I haven't reduced your substrate with Fe/HCl but I have successfully reduced 2,5-dichloronitrobenzene with this method and it works fine as long as you can team distil the product out of the reaction mixture. Sn/HCl will also work well but again steam distillation is required or at least the simplest work-up.

As you have access to borohydrides, maybe try this with a transition metal catalyst, there are loads of references scattered through SM. I have not tried nitroarene reductions with borohydrides but I was under the impression that a catalyst such as Ni was essential for complete reduction to an amine (I presume that this is your target).

In an aqueous environment at low temperatures I doubt that you will remove the chlorine before reduction. In hot alkaline solution you might convert part of the chloro compound into the corresponding phenol but my experience of 2-nitrochlorobenzene is that this requires very forcing conditions (autoclave) and the reaction is slow.

RustyShackleford - 28-4-2022 at 02:46

Fe/HCl......cmon bruh how did you try all that and NOT the most obvious thing

aab18011 - 28-4-2022 at 09:29

Yeah, I definitely wish I had tried to use iron filings. I ran out a month ago and never got more. I will scavenge around for some. And yes I feel the shame.

By the way, I have nickel acetate, will that be an okay replacement to pure nickel as a catalyst, or should I use something like copper sulfate (of which I have around 2 kg of)?

Did not realize steam distiliation is required. I thought I could extract it.

Thanks Rusty and Boffis!

aab18011 - 28-4-2022 at 11:49

What do you guys think about this method?
https://link.springer.com/article/10.1007/s12039-021-01940-3

Rice and CuSO4 with NaBH4? Seems freaking awesome!

AvBaeyer - 28-4-2022 at 18:55

Your biggest problem is that you are probably also reducing off the chlorine atom or involving that in some side reactions. The chlorine is quite reactive as it is ortho to the nitro group. Take some time to become familiar with literature about the reduction of o-halonitro arenes. There is plenty out there if try hard enough to find the information.

AvB

aab18011 - 29-4-2022 at 07:07

Quote: Originally posted by AvBaeyer  
Your biggest problem is that you are probably also reducing off the chlorine atom or involving that in some side reactions. The chlorine is quite reactive as it is ortho to the nitro group. Take some time to become familiar with literature about the reduction of o-halonitro arenes. There is plenty out there if try hard enough to find the information.

AvB


Damn, I was worried about that. I made some weird green colored oil, which definitely isnt the color of the azo I was trying to make. So im assuming it cleaved off a chlorine and left a nice reactive carbon. That probably means the cleaved ring probably did a subsitution on another uncleaved ring.

I will try and distill it/fraction it, and see if i get some clean oil. I have a feeling I have a lot of unreacted reagent that is dissolving the green compound. Possibly I can IR it and sneak a NMR in of the compound.

Thanks AvB

Triflic Acid - 3-5-2022 at 06:28

Using Mg metal in methanol has worked well for me in the past, when I was making dizaotoluene, from p-nitrotoluene. You might have an issue with the chlorine doing a grinard, which would break all hell loose. Also, wrkp is a pain since you get a shit-ton of Mg(OH)2. And if you plan to do this, I would recommend ice bath, condesor, and slow addition of the nitro compound, its really exothermic once it gets going, and you get flash boiling if you try to do it all at once.

UC235 - 3-5-2022 at 16:44

Mechanistically, this should be pretty easy. I suspect part of the issue is the material having nil solubility in water.

Perhaps this non-aqueous approach would be better? Granted it's tett lett so who the hell knows if it will work.



[Edited on 4-5-2022 by UC235]



[Edited on 4-5-2022 by UC235]

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