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Author: Subject: Making dichloromethane from methane/chlorine
Junk_Enginerd
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[*] posted on 20-9-2020 at 12:11
Making dichloromethane from methane/chlorine


I want to have a go at synthesizing DCM, for no particular reason other than it being challenging. One route, according to the SM wiki, is the reaction of chlorine gas and methane gas at high temps.

So I've figured out ways to make both chlorine and methane. The tricky part is to react them at a high temperature and gather the DCM. I had an idea on how to do this though. How about leading both gasses into a cooled large ish container(ideally purged from oxygen to not have a methane explosion). In this container, there would be a small heating element, keeping maybe 800°C. Gas would slush around, enter the high temperature vicinity of the coil, combine to DCM(or another chloromethane which is fine) and then condense on the containers cooled walls.

Does the principle seem sound? I worry about reactions with the heating element itself. Chlorine is quite a nasty thing and reacts with many materials. Will hot copper for example hold up against chlorine? And, copper being a catalyst, might I get some weird catalyzing effect and up with somerhing entirely different? Is stainless steel better?
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macckone
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[*] posted on 20-9-2020 at 13:48


Neither copper nor stainless steel will withstand 800C chlorine and hydrogen chloride.
You want a heated quartz tube.
Passing the gas into a quartz tube with UV light will also yield a reaction.
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[*] posted on 20-9-2020 at 15:17


This is a can of worms, there are two main routes to DCM, the one you have chosen is the direct chlorination route which suffers (or is an advantage ) from it making multiple chlorinated methanes. Then comes the fun of separating them. The byproduct is lots of HCL.

The other technique is to use HCL and methanol to form methyl chloride under catalytic Friedel- Craft conditions if done in the gas phase, or using metal chlorides in the liquid phase, and then chlorinate it with chlorine. This makes more of what you want but methyl chloride isn't something you want in your near vicinity for very long in any appreciable concentration.

Then there is the use of copper chlorides to chlorinate methane. Cuprous chloride is converted to cupric chloride to make methyl chloride. HCl is a byproduct which can be used to regenerate the cuprous chloride when 1/2 mol O2 is introduced per mol of cupric chloride.

Other schemes have been devised to close this cycle and an innovative and elegant one is to react methane, HCl, chlorine and air in a tube furnace to essentially combust the HCl to generate chlorine. Cuprous chloride, as well as potassium and zinc chlorides are used catalytically.
In a non industrial setting addition of air in these reactions has the potential to form the deadly phosgene, so it's chemically elegant but not something to get wrong.

Other milder chlorinating agents like sulfuryl chloride can be used, and there are exotic combinations of metal chlorides and sulphur trioxides to consider.
All of these use or generate potentially deadly gasses. High temperatures use of specific materials for the reactions and separations make this more than just a challenge.

I'd tread very carefully with this project.


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Junk_Enginerd
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[*] posted on 20-9-2020 at 23:45


Quote: Originally posted by macckone  
Neither copper nor stainless steel will withstand 800C chlorine and hydrogen chloride.
You want a heated quartz tube.
Passing the gas into a quartz tube with UV light will also yield a reaction.


Hm. I suspected as much. Well, I do glass work as well, so perhaps I could make it work anyway. I have no quartz glass, but 800°C is within borosilicate territory. Maybe it'll be semi fluid, but a design that doesn't depend on the glass for structural integrity should work. Covering a heating wire in glass perhaps?

Quote: Originally posted by Chemetix  
This is a can of worms, there are two main routes to DCM, the one you have chosen is the direct chlorination route which suffers (or is an advantage ) from it making multiple chlorinated methanes. Then comes the fun of separating them. The byproduct is lots of HCL.

The other technique is to use HCL and methanol to form methyl chloride under catalytic Friedel- Craft conditions if done in the gas phase, or using metal chlorides in the liquid phase, and then chlorinate it with chlorine. This makes more of what you want but methyl chloride isn't something you want in your near vicinity for very long in any appreciable concentration.

Then there is the use of copper chlorides to chlorinate methane. Cuprous chloride is converted to cupric chloride to make methyl chloride. HCl is a byproduct which can be used to regenerate the cuprous chloride when 1/2 mol O2 is introduced per mol of cupric chloride.

Other schemes have been devised to close this cycle and an innovative and elegant one is to react methane, HCl, chlorine and air in a tube furnace to essentially combust the HCl to generate chlorine. Cuprous chloride, as well as potassium and zinc chlorides are used catalytically.
In a non industrial setting addition of air in these reactions has the potential to form the deadly phosgene, so it's chemically elegant but not something to get wrong.

Other milder chlorinating agents like sulfuryl chloride can be used, and there are exotic combinations of metal chlorides and sulphur trioxides to consider.
All of these use or generate potentially deadly gasses. High temperatures use of specific materials for the reactions and separations make this more than just a challenge.

I'd tread very carefully with this project.




Yes, I'm aware I'll get a soup of different chlorinated methanes, but I think it's quite fine. The "novelty" end use of the product is as a solvent for 3d-prints, and if I recall correctly most chloromethanes are pretty similar as far as solvents go.

Plus, a separation step might be educational too. I mean, I could probably just buy DCM if that was the point, but it's just an interesting synthesis.

I'm not familiar enough with catalytic processes to feel like it would be worth the trouble. I'd just be fumbling in the dark and may not learn much, plus the catalytics are usually quite difficult to find.

Sulfuryl chloride eh? That's something I've at least noted down on my list of synthesisable compounds...

I've made oleum with sulfur trioxide before, so I consider myself perfectly capable to handle most toxic compounds. The only ones I'm uncomfortable dealing with it sneaky stuff like H2S and cyanides.
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[*] posted on 22-9-2020 at 16:03


Even if you keep out oxygen, the reaction of methane and chloride could very well be explsoive in the wrong amounts, so this would be very tough. I would start with making chloroform from acetone and bleach, a more approachable synthesis that is well documented on this site (use the search engine). Making DCM is about 10-100 times harder, so I would walk before I attempt to fly. And chloroform is good for nearly everthing that DCM is good for. Even as an experienced chemist, I would be wary of making DCM by radical chlorination, and I have done some wild stuff.
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[*] posted on 24-9-2020 at 11:22


Quote: Originally posted by Dr.Bob  
Even if you keep out oxygen, the reaction of methane and chloride could very well be explsoive in the wrong amounts, so this would be very tough. I would start with making chloroform from acetone and bleach, a more approachable synthesis that is well documented on this site (use the search engine). Making DCM is about 10-100 times harder, so I would walk before I attempt to fly. And chloroform is good for nearly everthing that DCM is good for. Even as an experienced chemist, I would be wary of making DCM by radical chlorination, and I have done some wild stuff.


I have made chloroform. It went well, and it's a great solvent, but it's such a ridiculous bulk of ingredients for a laughably small amount of chloroform. I don't have a source for really cheap sodium hypochlorite, so it gets expensive, or I need to muck about with the mess calcium hypochlorite makes.

Anyway, as I said earlier this is not really about making DCM, it's about trying something new and learning while doing it. I fully expect to fail at first, and have at it until I know the process. I

'm fine with explosions. A small gas explosion isn't that bad if you're prepared for it and do it outdoors, especially one that isn't ideal and stoichiometric. Face shield, gloves and anything more than a t shirt is enough to guard against that. Heh, and before you say I'm stupid to assume that: that's not an assumption as much as it is experience. Yeah yeah, might still sound stupid but I've made it to 30 without killing myself so I think I deserve some credit considering the hobbies I have lol. At least I'm not blowing someone else up. ;)
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