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Author: Subject: Dichloromethane from methanol?
DJF90
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[*] posted on 23-9-2008 at 09:21


Hydrochlorinate? You mean use HCl in a nucleophillic substitution reaction? I dont think it would work like that but I need to polish up on my substition/elimination "rules"... As for the further chlorination, there are many side products as it is free radical substitution occuring (unless you have another method?) and these variety of products can be difficult to separate.
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Sauron
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[*] posted on 23-9-2008 at 14:42


Using thionyl chloride on methanol gets you SO2, HCl and MeCl, three gases, which would need to be seperated. A bit of a muddle.

An elegant way to prepare methyl chloride is th react cyanuric chloride with methanol (excess methanol) at 15 C below reflux, then cold trap the MeCl. No HCl is produced. A dry ice/alcohol dewar condenser will do fine and the MeCl can be stores in a lecture bottle or (better) Sure/Pac cylinder with a brass control valve till needed. There's an article in JACS on this method of preparing alkyl chlorides from alcohols and I have posted it previously.

For some idea of what might happen on direct chlorination of methanol with Cl2, consider carefully the elemental chlorination of ethanol. Ethanol is oxidized by chlorine to acetaldehyde, probably via ethyl hypochlorite. Acetaldehyde is smoothly chlorinated to mainly dichloroacetaldehyde, then the chlorination slows and becomes less efficient while the final chlorine is added to produce chloral (trichloroacetaldehyde).

Therefore I suggest to you that methyl hypochlorite as intermediate to formaldehyde (methanal) is a BAD IDEA as it tends to go BOOM and in any case formaldehyde is not going to yield any MeCl or DCM.

[Edited on 24-9-2008 by Sauron]




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