Panache
International Hazard
Posts: 1290
Registered: 18-10-2007
Member Is Offline
Mood: Instead of being my deliverance, she had a resemblance to a Kat named Frankenstein
|
|
Koh and dcm
Solid Koh and dcm should never be mixed, what's the understood pathway for this beaker go boom sequence.
Does it hold for aqueous Koh solutions?
|
|
|
Texium
Administrator
Posts: 4569
Registered: 11-1-2014
Location: Salt Lake City
Member Is Offline
Mood: PhD candidate!
|
|
It’s well documented that chloroform reacts with bases, including aqueous hydroxides, to eliminate HCl and generate dichlorocarbene. Although DCM is
not as acidic as chloroform, it’s likely that an analogous reaction to form chlorocarbene is possible, though I can’t find a solid reference with
experimental evidence to support that.
|
|
|
woelen
Super Administrator
Posts: 8012
Registered: 20-8-2005
Location: Netherlands
Member Is Offline
Mood: interested
|
|
I have done that actual experiment with KOH (or NaOH) and CH2Cl2. I added the solid, also did experiments with solutions and with mixes with alcohol.
No reaction occurs at all.
|
|
|
AvBaeyer
National Hazard
Posts: 649
Registered: 25-2-2014
Location: CA
Member Is Offline
Mood: No Mood
|
|
I have run alkylation reactions using powdered KOH in DCM at ice bath temps with no problems.
AvB
|
|
|
Texium
|
Thread Moved
28-5-2022 at 18:34 |
Texium
Administrator
Posts: 4569
Registered: 11-1-2014
Location: Salt Lake City
Member Is Offline
Mood: PhD candidate!
|
|
Good to know then that that advice is likely based on an incorrect assumption that DCM would react with bases in the same way as chloroform. It’s
aggravating how those sort of rumors spread and can even become “conventional wisdom.”
|
|
|
Parakeet
Hazard to Self
Posts: 74
Registered: 22-12-2022
Location: Japan
Member Is Offline
Mood: V (V)
|
|
DCM+NaOH?
I came up with a crazy idea:
Does DCM react with sodium hydroxide to form formaldehyde?
CH2Cl2+2NaOH→HCHO+2NaCl+H2O
But I have an impression that alkyl halide + strong base is a bad idea, which comes from the reaction of chloroform and sodium hydroxide to generate
dichlorocarbene.
I would really appreciate if anyone could tell me what would happen before I screw up and accidentally make a fire ball.
|
|
|
andyloris
Harmless
Posts: 49
Registered: 22-9-2022
Location: France
Member Is Offline
Mood: Lazy
|
|
I am pretty sure NaOH is insoluble in DCM. So I guess the reaction will not happen.
Also, 1,2-Dichloroethane is very resistant to nucleophilic substitutions, so I am guessing it is gonna be the same with DCM.
Always trust your first idea, especially if you only have one.
|
|
|
Texium
Administrator
Posts: 4569
Registered: 11-1-2014
Location: Salt Lake City
Member Is Offline
Mood: PhD candidate!
|
|
Its also insoluble in
chloroform but it most certainly reacts. The solubility doesn’t matter here. What matters is that chloroform has a pKa of about 15. It’s quite
acidic as far as carbon acids go. More acidic than acetone. DCM’s pKa is much higher. I can’t find a source for what it is exactly, but it should
be sufficiently high to not be deprotonated by NaOH. I would guess that it’s at least 25.
|
|
|
Parakeet
Hazard to Self
Posts: 74
Registered: 22-12-2022
Location: Japan
Member Is Offline
Mood: V (V)
|
|
So, no reaction happenes because it's not acidic enough?
I was acutually thinking that SN2 or something might happen to produce gem-diol. But, if dichloroethane is resistant to nucleophilic substitutions,
there's little chance...
|
|
|
Texium
Administrator
Posts: 4569
Registered: 11-1-2014
Location: Salt Lake City
Member Is Offline
Mood: PhD candidate!
|
|
No, DCM definitely won’t undergo nucleophilic substitution with hydroxide. I honestly hadn’t even thought about that possibility because it’s
generally considered to be inert towards milder nucleophiles.
Chloroform doesn’t undergo nucleophilic substitution either. Its reactivity towards bases is due to its acidity.
[Edited on 11-27-2023 by Texium]
|
|
|
woelen
Super Administrator
Posts: 8012
Registered: 20-8-2005
Location: Netherlands
Member Is Offline
Mood: interested
|
|
I have personal experience with CH2Cl2 and hydroxide. They do not react with each other, not when the solid NaOH is added to CH2Cl2, nor when the
solution of NaOH in water is added to CH2Cl2 and the two liquids are shaken vigorously. In the latter case, the liquids simply separate again.
With CHCl3 things are different. CHCl3 is more reactive than CH2Cl2. CHCl3 does not give a violent reaction with NaOH, but they do react.
|
|
|
unionised
International Hazard
Posts: 5124
Registered: 1-11-2003
Location: UK
Member Is Offline
Mood: No Mood
|
|
Formaldehyde is not stable in the presence of NaOH
|
|
|
Parakeet
Hazard to Self
Posts: 74
Registered: 22-12-2022
Location: Japan
Member Is Offline
Mood: V (V)
|
|
Okay, seems it was a shallow idea.
Thank you for saving me from wasting the reagents.
|
|
|
Keras
National Hazard
Posts: 887
Registered: 20-8-2018
Location: (48, 2)
Member Is Offline
|
|
Quote: Originally posted by woelen  | | With CHCl3 things are different. CHCl3 is more reactive than CH2Cl2. CHCl3 does not give a violent reaction with NaOH, but they do react.
|
This reaction is quite exothermic, if my experiment at synthesising salicylaldehyde from phenol and chloroform is anything to go by.
|
|
|
Texium
|
Threads Merged
5-12-2023 at 13:40 |
![[*]](images/xpblue/default_icon.gif){kind=icon}
