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Author: Subject: Need help finding a non flammable low temp boiling liquid
aromaticfanatic
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[*] posted on 19-12-2020 at 16:15
Need help finding a non flammable low temp boiling liquid


I need to separate some nitrotoluene isomers for benzocaine but the issue is my previous plan of slowly cooling down the isomer mix via a styrofoam box and some computer duster was cut short by seeing a very low flash point of -50C. I don't want to fill a box with loads of flammable vapor. I understand it's not crazy flammable but why risk it.

r134a refrigerant was my next choice of low boiling liquid since the flash point was 351F but I found out it's a super potent green house gas and I can be fined up to $27,000 per day of releasing it. I don't want to be doing something illegal that costs that much too. My computer duster would not be illegal to use but I'd have loads of flammable vapor in a confined space.

I don't have access to dry ice since no one here sells any (thanks to all you who made dry ice bombs) and all the other potential things I can think of that would provide sufficient cooling and are readily available at stores are all flammable.

Does anyone know of anything that could substitute it?

And no I can't use a freezer because I don't have a chemical freezer. I've already tried cooling the isomer mix via chilled salt water and it worked, but it worked too quickly and I don't know if I have the filtration set up to make it work with that sludge.


**important edit**
I should've clarified that the boiling point of the liquid (or sublimating/melting point of a solid) needs to be -15C or below. Liquid nitrogen is too cold. It needs to cool the nitrotoluenes to around -10 to -15C so I think the lowest I could go is around -50C melting/boiling point. Sorry about that mixup.


To put it simply I need to cool the MNT isomer mix slowly to around -15C and I am trying to use low boiling liquids to achieve the goal but I am open to other methods so long as they don't require much.

I've thought of adding powdered ammonium nitrate and salt to a bunch of ice cubes. Not sure how well that'd work though since the cold temperature would need to be maintained for a while to allow for the MNT isomer mix to chill slowly via convection.

[Edited on 20-12-2020 by aromaticfanatic]




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Antigua
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[*] posted on 19-12-2020 at 16:30


Just DCM? Or is that out of reach for you?
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karlos³
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[*] posted on 19-12-2020 at 16:46


If you can't get DCM, make chloroform, thats always accessible.
And with, I think 55°C, its a formidably low boiling solvent.

But it seems you require a sub-room temperature boiling solvent, some freon I guess?
They are really hard to get nowadays.
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aromaticfanatic
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[*] posted on 19-12-2020 at 17:31


Quote: Originally posted by karlos³  
If you can't get DCM, make chloroform, thats always accessible.
And with, I think 55°C, its a formidably low boiling solvent.

But it seems you require a sub-room temperature boiling solvent, some freon I guess?
They are really hard to get nowadays.


Oh yea I should have clarified that the liquid needs to boil at around at least -15C since it needs to chill the mononitrotoluene to around that point for the para product to crash out.

I believe freon falls under that whole "release this and you get fined" thing.

I think I may have myself in a deadlock with this one. I might have to try something else or just accept the risk of fire and plan accordingly. I really don't like that though.

I find it ironic how the same chemical that is illegal to release into the atmosphere in the car context (AC systems) is often the same chemical in computer duster. Sadly my computer duster doesn't have tetrafluoroethane or else I would use it.




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aromaticfanatic
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[*] posted on 19-12-2020 at 17:35


Quote: Originally posted by Antigua  
Just DCM? Or is that out of reach for you?


I completely forgot to say that the liquid or solid needs to have a melting point or boiling point of around -20C. The goal is to chill the MNT isomer mix to around -15C in order to crash the para isomer out. I might look into getting a very large piece of metal or something to reach -20 in the freezer and then putting that in the box. I'm just worried how well that would actually chill the MNT isomer mix. I don't think a block of steel that I could find would be able to chill the mix to that temperature. Tricky stuff.




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Deathunter88
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[*] posted on 19-12-2020 at 17:47


Just use a normal freezer.
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aromaticfanatic
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[*] posted on 19-12-2020 at 17:53


Quote: Originally posted by Deathunter88  
Just use a normal freezer.


I can't. It's not viable for me to buy a freezer just for the lab right now and I am not about to put nitrotoluenes near food.

I wish I could but that's a horrible idea.

I've thought about running salt water lines from inside the freezer to inside the styrofoam box but I'd have to leave the freezer open for that to work in my case. I'm thinking of maybe adding a load of ice cubes on the bottom of the box and adding ammonium nitrate and salt to it. The only concern I have is that I don't think it will sustain the cold temperatures long enough for the isomer mix to cool down the the required temp through convection.

[Edited on 20-12-2020 by aromaticfanatic]




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karlos³
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[*] posted on 19-12-2020 at 18:19


Whats with CaCl2/ice? That can cool down to over(below) -30°C?
That should be sufficient for your purpose.
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aromaticfanatic
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[*] posted on 19-12-2020 at 18:25


Quote: Originally posted by karlos³  
Whats with CaCl2/ice? That can cool down to over(below) -30°C?
That should be sufficient for your purpose.


Good point I have been looking into various salts to add to ice and CaCl2 is indeed a good candidate. I don't have much of it right now. I have found that NaCl is able to cool down to -17C. With no gas production from boiling liquids I could seal the entire box off to allow for the best insulation as possible.

I'll see if I can use road salt. I know my road salt has NaCl, CaCl2, and MgCl2 so that should work very well. I'm going to try some test runs without the nitrotoluenes. I'll see how cold I can get it and if I can get the temp to be cold long enough for it to freeze water by convection. If I'm able to pull that off then the isomer mix should pose little challenge.

Thanks for that idea. Do you think adding ammonium nitrate would help? I know it doesn't really lower the melting point of ice by much but it absorbs a lot of heat which should help. I might make a mix of road salt and ammonium nitrate pellets and throw that onto the ice.




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RedDwarf
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[*] posted on 20-12-2020 at 07:41


Dry ice?
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Heptylene
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[*] posted on 20-12-2020 at 09:13


To make an ice/salt bath, the CaCl2 has to be hexahydrate, not the dihydrate usually sold for dehumidifiers. Something to keep in mind.

You can use snow as your source of ice, this will make a very nice slurry with the CaCl2. Put the snow and CaCl2 in separate containers in the freezer before the experiment. The -20°C of the ice and CaCl2 will give you a headstart. When you're ready, mix them thoroughly until you have a homogeneous mixture. I managed to get -35 °C this way.
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[*] posted on 20-12-2020 at 09:51


Ortho nitrotoluene melts at -10, the para at 53. When you cool a mixture to -16 (coldest I tried) you will still have a liquid fraction. What I think happens is that the para freezes out but some para and or meta nitrotoluene dissolved in the ortho depresses the meting point a bit.

What you can do is make a concentrated CaCl2 solution and put that in a freezer, use this to cool your nitrotoluene.
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aromaticfanatic
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[*] posted on 20-12-2020 at 23:45


Quote: Originally posted by RedDwarf  
Dry ice?

Yea I think I mentioned I didn't have access to it but after talking to some people I was able to find someone who'd sell some so this thread is semi useless to me but I think it's still bringing forward valuable info.


"To make an ice/salt bath, the CaCl2 has to be hexahydrate, not the dihydrate usually sold for dehumidifiers. Something to keep in mind.

You can use snow as your source of ice, this will make a very nice slurry with the CaCl2. Put the snow and CaCl2 in separate containers in the freezer before the experiment. The -20°C of the ice and CaCl2 will give you a headstart. When you're ready, mix them thoroughly until you have a homogeneous mixture. I managed to get -35 °C this way."

I was unaware of that thank you for that info! I have thought of putting some ice cubes in the freezer to get to -20C and then adding the salt but it's very nice knowing the practical temperature reached. Thanks!


"Ortho nitrotoluene melts at -10, the para at 53. When you cool a mixture to -16 (coldest I tried) you will still have a liquid fraction. What I think happens is that the para freezes out but some para and or meta nitrotoluene dissolved in the ortho depresses the meting point a bit.

What you can do is make a concentrated CaCl2 solution and put that in a freezer, use this to cool your nitrotoluene."

I have tried the latter with NaCl and it works but it was in direct contact with the beaker causing the para to crystallize too fast and make small crystals. I am working on a vacuum filtration set up that should allow me to even filter the sludge that I had made previously. I also managed to get a source of dry ice (I was ecstatic when I found one!) so I think this project is finally ready to go. I'm not the most skilled chemist and it often takes me a few tries to get an experiment right. I guess we'll see though. This whole benzocaine synthesis starting from carb cleaner was a test of my skills anyway so I suppose that a proper failure (not due lack of equipment) will set the bar for my skill set.

Yea the para isomer crashes out at around -10 to -15C from what I've seen. When chilled slowly the para crystals are large enough to be able to practically decant off the remaining ortho isomer. That's what I would like as it should give the highest and purest yield of the para isomer.

I believe the isomers form a bit of a eutectic mixture but I am not sure what exactly depresses the freezing point. There was a write up by someone on here and he tried the freeze method followed by vacuum fractional distillation. The freezing out of the isomer recovered around half of what was actually formed. He got the rest out through distillation. So there is definitely a considerable amount of para isomer left in the remaining liquid.




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Tsjerk
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[*] posted on 21-12-2020 at 02:16


What do you want to accomplish with dry ice? Do you want to freeze the mixture and thaw at -20 to separate? Because I don't think that would give you any better separation compared to crystallization at -20 to start with.

Also, how sure are you there is no toluene left in there?
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[*] posted on 21-12-2020 at 03:52


My chest freezer gets to -20 or lower.
If I was doing this, I would probably fill a styofoam box with water and place a smaller container inside and the freeze: the result would be a vessel made of ice with styrofoam insulation.
Then inside the depression in the ice I would add crushed ice or ice cubes and CaCl2, both pre-chilled to -20. That should make for a low temp ice bath with enough thermal mass to last a long time.

My $0.02.
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aromaticfanatic
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[*] posted on 21-12-2020 at 09:17


Quote: Originally posted by Tsjerk  
What do you want to accomplish with dry ice? Do you want to freeze the mixture and thaw at -20 to separate? Because I don't think that would give you any better separation compared to crystallization at -20 to start with.

Also, how sure are you there is no toluene left in there?


Not exactly. I'd place the dry ice at the bottom of the box and place the beaker with the isomers over the dry ice so that it is not in direct contact. The dry ice should cool the isomer mix by convection which should cool it much slower than if I were to put whatever I'm using to cool the isomers with in direct contact. I'll have a thermometer in the box that sticks out so that I know what temp the isomer mix is at. I'd remove the isomer mix at around -15C and filter.

There will definitely be traces of toluene left but not enough to interfere. I've done this reaction before and the para product did crystallize out. The problem was that I only had gravity filtration and the crystals were far too small to separate easily before warming back up.

[Edited on 21-12-2020 by aromaticfanatic]




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aromaticfanatic
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[*] posted on 21-12-2020 at 09:19


Quote: Originally posted by j_sum1  
My chest freezer gets to -20 or lower.
If I was doing this, I would probably fill a styofoam box with water and place a smaller container inside and the freeze: the result would be a vessel made of ice with styrofoam insulation.
Then inside the depression in the ice I would add crushed ice or ice cubes and CaCl2, both pre-chilled to -20. That should make for a low temp ice bath with enough thermal mass to last a long time.

My $0.02.


Thank you, I'll have to keep that in mind in case my next try fails.




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