Intergalactic_Captain
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Melt-Phase NaHSO4/xNO3 nitration of p-dichlorobenzene?
The question is pretty straight-forward. I've been looking over some articles on p-dcb nitration, and it seems that the general consensus is 95%+
yeilds w/ mixed acids at (comparatively) high temperatures...It's been a few years since I've attempted this, but I remember it being a very simple
synth (though quite lachrymating) with Rooto H2SO4/ and either NH4NO3 or KNO3 (can't remember which one I used).
Unfortunately, due to budget constraints, I am out of acid for a few weeks. I do, however, have a sizable amount of NaHSO4 looking for a good use,
along with about 50g of NH4NO3 and ~150g KNO3. I tried making a bit of HNO3 the other day, and the temp required to form a melt did not seem too high
to be feasible for the proposed reaction - Somewhat above the mp of p-dcb, but didn't seem to be runaway-high.
I'd ask this over in EM, but the mono-nitro material I'm after really has nothing to do with explosives...So, has anyone here had any experience with
melt-phase reactions, specifically nitrations? Anyone have a procedure I can go by before wasting materials? The working plan is to use a 5:2:1
molar ration of NaHSO4:KNO3:p-DCB at just the right temp to keep everything molten for ~30 min after all p-DCB is added - Perhaps it would be better
to mix everything dry and then heat it? Longer reaction time maybe? Possibly need more NaHSO4 due to the KNO3? I'm pretty sure this reaction will
work, it's just the specifics that need to be worked out - At least the workup'll be easy, though...I'm guessing mixing w/ hot water to dissolve all
the salts and popping out the hardened cake after cooling, followed by a hot Na2CO3 wash will take care of it.
Wow...That came out with more rambling than I thought. So, anyone with any practical experience feel like giving me some pointers?
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garage chemist
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Please tell, what is your desired end product and what do you want do to with it?
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Intergalactic_Captain
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Guess I wasn't clear enough - I want mono-nitrated paradichlorobenzene...2,5-dichloronitrobenzene.
Replacing the chlorines on p-DCB is a bitch and half, but a good bit of research has been done on reactions with the nitro derivative. For instance,
one ref I found (I'll post it tomorrow if I can dig it up) gave the anisole (ortho to the nitro) w/ MeOH and NaOH...Unclear as to whether it was a
bomb or reflux, but seemed a lot simpler than the p-DCB/NaOH bomb (mixed products, only ~20% overall conversion).
I guess the plan right now is to see how far I can go with substitution...Mothballs are just so cheap, they're practically begging to be chemically
molested. It'd be nice to go to 2-nitro-4-hydroxyanisole, but I'm betting that second chlorine is gonna be a good bit less reactive - Perhaps
swapping it with bromine would make it easier to work with, but that's a question for another day.
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not_important
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Problem I see is that your melt will need to be about 170 C, which is real close to where p-DCB's vapour pressure reaches 760 mmHg. It's tendency to
sublime makes refluxing a bit tricky, because it likes to form crystals in the cooler parts of the condenser, and if it's warm enough to melt the
p-DCB it's warm enough to encourage some sublimation.
I'm guessing that you may want to add a little water, to get a lower temperature melt.
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Intergalactic_Captain
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Attached is the article I mentioned regarding methanol, but I can't seem to make heads or tails of it...They claim great success using "Blom's
method," but I can't access the referenced article online - If class was in session I could get the hardcopy, but the library's an hour away and I've
got no wheels. If anyone could pull up the article and translate the experimental part, I'd greatly appreciate it.
Regarding the nitration, though, I didn't think it would be that hot. I've got the "pH down" swimming pool bisulfate, supposedly hydrated - I know it
sure as hell melts wayyy lower than 375C, as I was able to get a stable melt in an ethylene glycol bath (bad idea, but it was all I had at the time).
Since you mentioned it, I'm considering using a bit of water in the mix - Wouldn't it "weaken" the nitrating strength, though? I know it would make
it much easier to work with, but I'm worried about it just not working at all.
I think I'll give this a shot later today and see how it goes. It'll be done in an open container, so no condenser to worry about. I'll probably try
the melt first, and if it's too difficult to work with I'll let it cool, add a bit of water, and try again. In the meantime, anyone see a problem
with my proposed ratios? I pretty much just pulled them out of my ass, but they seem good enough.
Attachment: ja01421a022.pdf (672kB)
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Intergalactic_Captain
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Just gave it a shot in a 8:2:1 ratio - 150g NaHSO4, 25g KNO3, 20g p-DCB. The p-DCB was in slight excess, though apparently not enough. Mix was
heated in a 1-cup pyrex measuring cup on "medium" on my hotplate. Took ~30min to melt, held for 1 hour and crashed into ~2 cups cold water.
Filtered, neutralized in hot bicarb solution, waiting for it to cool right now to find yeild, though it doesn't look promising.
So far, it looks like this is a good method - The ratios need to be tweaked a good bit, though. My merck index shows p-DCB to be (water) insoluble,
and a little searching shows the mononitro compound to be insoluble as well. However, I ended up with orange washwater both times. Anyone know how
soluble the dinitro coumpound is, or what possible byproducts I may have made? It would appear that I had far too much nitrate in the mix - 2x molar
amount. Perhaps ~1.2 would work better, though too much nitric may be lost to the atmosphere.
One thing that repeated from last time, though, was immiscibility...The p-DCB layer floated atop the nitrating mix, and no amount of manual stirring
could mix them very well. I stirred it as best as possible, though the acid bubbling through the top layer seemed to be doing the job quite well.
I've got a bit of a conundrum though - I can't figure out how to separate the unreacted p-DCB from the mononitro compound...Distillation could work,
though I don't have the setup quite yet (bought my glass without realizing I needed stands!).
If you see me running, try to keep up.
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