Sauron
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SbCl5 Chlorination: Methyl Formate? Dimethyl Carbonate?
Normally the chlorination of these esters is done by Cl2 with UV photolysis.
In the case of methyl formate this is somewhat hazardous since the ester is volatile and mixtires of Cl2 and methyl formate vapor are explosive.
Once you get to the methyl chloroformate stage the stepwise perchlorination of the methyl group is undramatic.
So I was considering trying to use SbCl5 to put on the first Cl.
SbCl5 is known to chlorinate CS2 at room temperature, something PCl5 will not do.
So my proposed reaction is
SbCl5 + HC(O)OMe -> ClC(O)OMe + HCl + SbCl3
Passing Cl2 into methyl formate and SbCl3 ought to go same way, SbCl5 forms in situ.
This reaction is a lot safer sand UV. If it works of course.
I have previously posted the Org Syn prep of trichloromethyl chloroformate and the paper on the use of SbCl5 to prepare CCl4 from CS2. See those.
[Edited on 1-6-2009 by Sauron]
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panziandi
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Reaction of PCl5 with methyl formate is used to generate dichloromethyl methyl ether, unsure if the reaction with SbCl5 would behave similarly.
Organic Syntheses, Coll. Vol. 5, p.365 (1973); Vol. 47, p.51 (1967).
And SbCl5 is very powerful chlorinating agent, used IIRC to break up organic compounds.
I'd say that it would have to be used in minute, catalytic quantity at a cool temperature. Why not just chlorinate methyl formate using chlorine and a
UV bulb keeping the reaction mixture cold to prevent volatizing the ester and thus reduce risk of explosion. This was the method I was considering.
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DJF90
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I was considering the use of antimony pentachloride to chlorinate DCM to chloroform and carbon tet. as indicated a possibility in another thread. If
methyl formate can be chlorinated using SbCl5 as a catalyst then this is a potentially useful route to trichloromethyl chloroformate, aka. diphosgene,
and as such will open a few doors that were previously barred to us amateur chemists.
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Sauron
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The reasons for looking fir alternatives to UV chlorination of mrthyl formate are safety issues, sd Cl2 and methyl formate vaor form explosive
mixtures that can be ignited by US. Thus it mandatory to start irradiation before Cl2 is passed in and to limit rate so that all chlorine reacts
rather than accululating in the headspace.
It is perhaps worth considering the prep of methyl chloroformate from phosgene and methanol, using a toluene soln of phosgene, but it is a delicate
judgement as to which prep is more hazardous.
A way around both is to chlorinate dimethyl carbonate in CCl4 and obtain triphosgene - solid, hexachlorodimethyl carbonate which for many reactions is
a phosgenating agent almost as useful as diphosgene, although slower. Safer too.
PCl5 adds to the carbonyl to obtain 1m1-dichloromethyl methyl ether, NOT to be confused with 1,2-dichloromethyl ether. The product is useful and
noncarcinogenic, and if SbCl5 reacts this way I will be happy. anyway. SbCl5 is easier to come by than PCl5, especially if you make it from SbCl3.
[Edited on 3-6-2009 by Sauron]
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panziandi
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Sauron have you found anything more on the reaction of SbCl5 with methyl formate or dimethyl carbonate? I might get one of these two and chlorinate it
(distinct lack of SbCl3/SbCl5 at the moment however).
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Sauron
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Despite the thread titlr I do not think dimethyl carbonate is a candidate as it has no formyl hydrogens.
I priced SbCl3 and it is cheap and in local stock so I will buy a couple Kg and chlorinate it up to pentachloride. A lot cheaper than buying SbCk5. I
will just prepare what I need at any given time as the pentachloride is hard to store (highly corrosive.) So better to store as the trichloride.
From reactions of the pentachloride, the trichloride is recoverable as well.
But no I have not had time to spend on paper chase, I have been busy scanning Mellor.
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