Dichloromethane (Now healthier with 50% less chlorine!)

Chlorinated solvents are great solvents. The polarizability of chlorine, moderate electronegativity, moderate volatility, lack of acidic protons or reactivity - it all adds up to a great reaction medium. However, they usually are toxic.

Carbon tetrachloride, CCl4, used to find a lot of use, even in dry cleaning, but it's toxic, especially to the liver. Chloroform, CHCl3, is a little less toxic. And dichloromethane, CH2Cl2, is less toxic still.

A friend of mine used to joke that we'd use methyl chloride if only it weren't a gas.


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I don't think that methyl chloride would be relatively useful or safe, when compared against its poly-halogenated siblings, even if it were a liquid. Part of the increased reactivity (and toxicity) of methyl chloride is probably due to the absence of the stabilizing anomeric effect.

By Dave Pinkerton (not verified) on 01 May 2008 #permalink

But as dichloromethane is a less potent solvent, you'll need twice as much as if you were using the good ol' tetrachloride, won't you?

I know it is one of the simplest of all molecules ...but no structure pic..??

Working in a medical laboratory, performing toxicological and other extractions, this is a frequently used compound.



By ...tom... (not verified) on 01 May 2008 #permalink

Sometimes you can tell where a chemist is from based upon whether they say "dichloromethane" or "methylene chloride."

(help me out: how does the anomeric effect relate to stability/reactivity of methyl chloride vs dichloromethane?)

I used to use "trike", or trichloroethane, in an industrial valve shop I once worked in. It was used to wash valves and components of metal filings, etc. I always thought is was cool, literally and figuraively ( I was 17-18 at the time).

A few tidbits about each of the carbon chlorides:

I don't know much about its reactivity, but methyl chloride is extraordinarily flammable, due to it being a mostly carbon-and-hydrogen containing gas (by number of atoms, not weight). It'd probably make some HCl upon combustion, I don't know what else the Cl would form.
The third-largest single-building fire disaster in US history was caused by a leak of this stuff; this was the Cocoanut Grove fire in Boston. It was used as a refrigerant.
My grandmother was going to be there that one fateful night in 1942; I wouldn't exist if she did. o_o

I occasionally recycle petroleum solvents/thinners into waxy or gelled firestarters, but the one time I ran into something that contained methylene chloride (another name for this article's molecule, for those who don't know) I obviously didn't use it. It finds use as a paint stripper.

Chloroform is obviously famous for its ability to knock you out; mixing bleach with the wrong household chemicals, such as ammonia/alcohols (I think) can generate a cocktail of chlorinated compounds, perhaps chloroform if I recall correctly.

Carbon tetrachloride, thank God, isn't a fire-fighting chemical any more, because it actually wasn't immune to heat. It could be further oxidized to phosgene, COCl2, and maybe other nasty stuff too.

As for the comment about the anomeric effect, Wiki says this has to do with cyclohexane rings. How does this relate here?
I'm an undergrad student, and I've never heard of it.

Hi Barney and Dane,

The anomeric effect is invoked to explain why tetrahydropyran rings sometimes (surprisingly) adopt sterically congested conformations.

Molecular conformations, in which a lone pair of electrons from a hetero-atom are anti-periplanar to a an adjacent polarised bond, are stabilized.

Dichloromethane only has one conformation; It is set up so that there is a permanent donation of electron density from chlorine lone pairs into the C-Cl bond of its counterpart. In this way, dichloromethane is always stabilized by two pseudo-anomeric effects, and this effect makes it a fairly inert solvent.

Methyl chloride lacks this pseudo-anomeric effect and is thus a reactive electrophile. Of course, its sterically more-accessible carbon atom may also contribute to some of its increased reactivity.

By Dave Pinkerton (not verified) on 09 May 2008 #permalink