Sciencemadness Discussion Board

How to Reduce Trichloromethane to Dichloromethane?

LuckyWinner - 12-11-2020 at 05:03

trichloromethane can easily be made OTC.

reduction of an alcoholic solution of chloroform by zink and hydrochloric acid

CHCl3 + Zn + 2 HCl → CH2Cl2 + ZnCl2 + HCl
1 mol Chloroform + 1 mol ZN + 2mol HCL = 1mol CH2Cl2 + 1mol ZnCl2 + 1 mol HCl


Chemicals Needed
-------------------------
37% HCL contains 37g of HCL and 63g of water.
PURE HCL weights 36,46 g/mol that means you need
~200ml of 37% HCL solution to get 2 mol HCL.

Chloroform 135.42 g/mol , 1 mol
HCL 37% 200ml 240g (1.2g/ml density) ,2 mol HCL
ZINK 65,39 g mol , 1 mol
Ethanol/Methanol 300ml



Process
------------
setup for simple distillation, with
zink +chloroform + ethanol in flask (or methanol)
with strong mag stirring.

mix choroform and zink with several times its volume of alcohol.

then slowly drip in HCL from additonal funnel.
watch distill head temperature for DCM and Chloroform temperature.
try to keep it at ~40C. (BP of DCM)

distillate is a mix of chloroform and DCM and will be added to the flask again
for several further reductions.

Chloroform Boiling point: 61.2 °C
DCM Boiling point: 39.6 °C

after 3 runs do a fractional distillation to obtain pure DCM.

will this work?



Questions
---------------

1) how much ethanol to use, 300ml is enough?

2) do you need to activate the zink powder?

3)distillate should be re-added to flask or first always fractionally distilled
to separate out DCM from Chloroform?
DCM can not be reduced to chloromethane by zink.

4) why is there nobody writing about this since its banned in the EU from OTC.

5) overhead stirring necessary to increase yields?

6) would this reduction also work with Iron?


sources:
http://www.sciencemadness.org/smwiki/index.php/Dichlorometha...

DCM can also be prepared by reducing chloroform with hydrochloric acid and zinc metal in ethanol.
CHCl3 + Zn + 2 HCl → CH2Cl2 + ZnCl2 + HCl

source here claims a 20% yield on the chloroform used
https://books.google.nl/books?id=pdcBAAAAYAAJ&pg=PA522&a...

[Edited on 12-11-2020 by LuckyWinner]

[Edited on 12-11-2020 by LuckyWinner]

Fluorite - 12-11-2020 at 05:19

This should work nascent hydrogen is a strong reducing agent! This can also reduce arsenates to arsine! But idk why can't reduce silicates to silane :/
You can use sodium arsenite to reduce chcl3 to dcm but arsenites are toxic :(

[Edited on 12-11-2020 by Fluorite]

[Edited on 12-11-2020 by Fluorite]

Tsjerk - 12-11-2020 at 06:22

What do you need DCM for? Good chance chloroform would work instead as a solvent.

Also DCM is not banned in the EU.

https://www.deoplosmiddelspecialist.nl/kopen/dichloormethaan...

Limitation: max 20 liter for private customers.

Quote: Originally posted by Fluorite  
This should work nascent hydrogen is a strong reducing agent! This can also reduce arsenates to arsine! But idk why silicates can be reduced to silane :/
You can use sodium arsenite to reduce chcl3 to dcm but arsenites are toxic :(

[Edited on 12-11-2020 by Fluorite]


Right...

[Edited on 12-11-2020 by Tsjerk]

LuckyWinner - 12-11-2020 at 06:43

Quote: Originally posted by Tsjerk  
What do you need DCM for? Good chance chloroform would work instead as a solvent.

Also DCM is not banned in the EU.

https://www.deoplosmiddelspecialist.nl/kopen/dichloormethaan...

Limitation: max 20 liter for private customers.

Quote: Originally posted by Fluorite  
This should work nascent hydrogen is a strong reducing agent! This can also reduce arsenates to arsine! But idk why silicates can be reduced to silane :/
You can use sodium arsenite to reduce chcl3 to dcm but arsenites are toxic :(

[Edited on 12-11-2020 by Fluorite]


Right...

[Edited on 12-11-2020 by Tsjerk]


yes I know its not banned but what I mean its banned OTC as solvent and I dont
want to receive any chemical shipments by mail to my home address and risk being put on some 'terror-blacklist'.

you are smart, does this trichloromethane reduction work?

njl - 12-11-2020 at 07:18

It works (and has been discussed here before) but the yield is awful. You really are better off buying it. If you insist on not buying straight DCM, paint thinners are the usual source for amateur labs. It's one of those things that you're pretty much always better off buying.

Tsjerk - 12-11-2020 at 07:20

I don't know whether it works, maybe it does, maybe it doesn't.

Have a look at this discussion:

http://www.sciencemadness.org/talk/viewthread.php?tid=78041

LuckyWinner - 12-11-2020 at 08:21

Quote: Originally posted by Tsjerk  
I don't know whether it works, maybe it does, maybe it doesn't.

Have a look at this discussion:

http://www.sciencemadness.org/talk/viewthread.php?tid=78041


thats where I got my sources from, check out bottom of post 1
Quote:


If you do intend to try the dehalogenation of chloroform then i would personally suggest activating it first by washing with dillute HCl then water then ether then drying the shit out of it in a desiccator.
activated zinc dust doesn't keep well and will oxidize within a 24 hour span so use it quick or store under an inert atmosphere.

If the dehalogenation fails with activated zinc then i would possibly suspect its a flop.
...


So it would appear that both chloroform .. can be rapidly dechlorinated by iron powder in water to dichloromethane, which resists further dechlorination, with little degradation even after a month.
Now I'm curious if this method can be scaled up.
...



NOBODY posts any results or even trying this reaction, just speculation...

is there anything else more precise out there about this reaction except that one
short text from the 1800s... almost 150 years old!



[Edited on 12-11-2020 by LuckyWinner]

monolithic - 12-11-2020 at 08:54

I've been meaning to try this reaction for a while. It's impractical but might be worth it if there's absolutely no way for you to get DCM and you absolutely need DCM. I tried searching for other sources (a good keyword is reductive dechlorination) but couldn't find a lot of detail. Most reductive dechlorination research is found in environmental chemistry journals where they do this reaction with a huge excess of reducing agent, often with expensive catalyst, on a very dilute CCl4/CHCl3 (groundwater contamination, etc.)

Greene paper is here: http://www.sciencemadness.org/talk/viewthread.php?tid=78041&...

I don't think zinc needs to be activated since it will react just fine in the presence of ethanolic HCl. My idea is to perform the reaction on an ice bath which reduces condenser losses and may eliminate the need to "return the residue to the flask again" as the author puts it. I also wonder if Zn-Cu couple would be applicable or beneficial in this, I think I've seen it used on other dechlorination reactions before. I also wonder if there are any practical electrochemical reductions that are possible.

[Edited on 11-12-2020 by monolithic]

LuckyWinner - 12-11-2020 at 09:30

Quote: Originally posted by monolithic  
I've been meaning to try this reaction for a while. It's impractical but might be worth it if there's absolutely no way for you to get DCM and you absolutely need DCM. I tried searching for other sources (a good keyword is reductive dechlorination) but couldn't find a lot of detail. Most reductive dechlorination research is found in environmental chemistry journals where they do this reaction with a huge excess of reducing agent, often with expensive catalyst, on a very dilute CCl4/CHCl3 (groundwater contamination, etc.)

Greene paper is here: http://www.sciencemadness.org/talk/viewthread.php?tid=78041&...

I don't think zinc needs to be activated since it will react just fine in the presence of ethanolic HCl. My idea is to perform the reaction on an ice bath which reduces condenser losses and may eliminate the need to "return the residue to the flask again" as the author puts it. I also wonder if Zn-Cu couple would be applicable or beneficial in this, I think I've seen it used on other dechlorination reactions before. I also wonder if there are any practical electrochemical reductions that are possible.

[Edited on 11-12-2020 by monolithic]



that seems plausible.


anyone can confirm these are the proper amounts to do this reaction?

Chloroform 135.42 g/mol , 1 mol
HCL 37% 200ml 240g (1.2g/ml density) ,2 mol HCL
ZINK 65,39 g mol , 1 mol
Ethanol/Methanol 300ml

setup for simple distillation,
zink +chloroform + ethanol
with strong mag stirring.

slowly drip in HCL from additonal funnel.
try to keep addition at a rate to keep still head temp at ~40C. (BP of DCM)

receiving flask, do a fractional distillation to obtain pure DCM.

[Edited on 12-11-2020 by LuckyWinner]

Tsjerk - 12-11-2020 at 13:27

Nobody knows what the correct amounts are, as apparently nobody tried to do the reaction. Probably your calculations about stoichiometric amounts are correct.

macckone - 29-12-2020 at 11:40

Many places have now banned dcm. I cannot even get it from my lab supply company. I can still get it in paint remover a state away but it requires special order and has to be picked up since sale is banned in my state. Same with toluene now :( however i can theoretically distill gasoline the toluene content there has been reduced as well.