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amrhamed2
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[*] posted on 23-7-2009 at 15:15
triphosgene


I would like to ask about ur experience with syn of this reagent
Literature method used chlorination of dimethyl carbonate irradiated with uv lamp for 18 hours

I want to ask if there is any method to chlorinate the DMC in situ like using calcium hypochlorite to prepare chloroform .........I would like know ur opinion in that plz

The problem is that I find it hard to produce chlorine gas for 18 hours continuously




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len1
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[*] posted on 23-7-2009 at 20:46


The generator in prepublication can produce Cl2 for any length of time - whats important is the number of moles. Is there any mention of the excess chlorine required.
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Arrhenius
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[*] posted on 23-7-2009 at 21:41


Calcium hypochlorite will likely destroy the reagent. The reaction would have to be strictly anhydrous and completely free of even the weakest nucleophile. If you can buy this reagent I think you're far better off doing so. Every time I open the bottle I get the nice 'fresh cut grass' smell of phosgene. Mind you that the subsequent reactions with triphosgene can be extremely challenging as well.
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[*] posted on 24-7-2009 at 01:00


Quote: Originally posted by Arrhenius  
Calcium hypochlorite will likely destroy the reagent. The reaction would have to be strictly anhydrous and completely free of even the weakest nucleophile. If you can buy this reagent I think you're far better off doing so. Every time I open the bottle I get the nice 'fresh cut grass' smell of phosgene. Mind you that the subsequent reactions with triphosgene can be extremely challenging as well.


? My undestanding was that if you can smell phosgene you are breathing it at well beyond the concentration at which its doing you harm. Have you experienced any after effects after smelling it?
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[*] posted on 24-7-2009 at 11:03


If you can smell it you're over your OSHA / NIOSH 8 hour average, but not necessarily into the harmful range. There is a table available of the physiological responses to increasing phosgene concentration (Phosgene and related carbonyl halides: ISBN 978-0444824455 ) that gives a much better indicator of what kind of exposures are tolerable and beyond tolerable (for short exposures). However if you think that it smells like fresh cut grass you are smelling doses that are almost so low as to be imperceptible. Yes, you see the smell referenced as such everywhere, but that description is antiquated, anyone with a chemical background that has smelled phosgene can give you a better/more accurate description of the smell which most certainly only resembles fresh cut grass/hay on the most superficial level.

With regards to triphosgene, there is another method using ethylene carbonate as the starting material. I don't remember much about it but it was discussed on this forum somewhere. I doubt the reaction conditions are any more accommodating but it might be worth a look.

[Edited on 7/24/2009 by BromicAcid]




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Arrhenius
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[*] posted on 27-7-2009 at 21:10


Len1: Sure, it's probably harmful. I felt funny once after using it, but ultimately decided it was a placebo effect. Smelling it is well below the lethal level undoubtedly.

BromicAcid: Ok, don't trust me... it really does smell a bit like cut grass. If this description is 'antiquated', either I'm old, or the human nose has evolved in recent years. Perhaps you can give us all a better/more accurate description. I'll send you some triphosgene if you need to check again what it smells like.
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[*] posted on 28-7-2009 at 13:58


Four days a week I work with phosgene and occasionally triphosgene. If you know what chlorinated hydrocarbons smell like, you've got half of the equation right there, if you know what hydrogen chloride smells like you've got the other. It is sweet, bitingly so at first and pungent, burning... I'm just saying that people fall back on the freshly mown hay description as a crutch, people in WWI were describing it that way because they had no chemical background on which to base their descriptions on. I've smelled fresh cut grass and I honestly don't see much of a comparison. Historically it's been related to fresh cut hay, not sure if there is a difference but there could be. Personally, if I had to compare the smell to something simple and OTC, I would compare it to the smell of an isle of new shoes :D



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Arrhenius
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[*] posted on 28-7-2009 at 19:42


Haha.. I'll be honest then... The smell freaks me out enough to not want to try to characterize its odor. I just open the bottle, weigh what I need as quick as possible and move on. I do find its use to be a bit of a pain in the ass sometimes though. Have you managed to make any chloroformates with it?
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[*] posted on 28-7-2009 at 22:45


The smell of freshly cut hay (both dry and just from the meadow) is a smell I have smelt many times and which I do like (I associate it with good summer days). In no way can this smell be compared with the acrid smell of HCl and also the sweetish smell of chlorinated hydrocarbons is quite different. So, if the smell of phosgene is like a mix of the smells of HCl and chlorinated hydrocarbons, then I'm 100% sure that this is not the same as the smell of freshly cut grass or freshly cut hay. I however never smelled phosgene and I think it is good if it keeps that way :P



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entropy51
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[*] posted on 29-7-2009 at 08:45


Pure COCl2 smells a little like fresh corn, especially green corn.

Moisture in the air hydrolyzes it to HCl and then it smells like, well, HCl.

Woelen, admit it. You want to make just a little, 100 mg or so.
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[*] posted on 30-7-2009 at 06:29


Quote: Originally posted by entropy51  
Woelen, admit it. You want to make just a little, 100 mg or so.
Ok ok... just a little :P, just to get the idea of it and then quickly move on to another funny thing like ClN3 or BrCN.



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[*] posted on 30-7-2009 at 23:31


The key paper on preparation of hexachlorodimethyl carbonate is in Angewandte Chemi by Eckerd and the English translation is in the International Edition of same. I believe it has already been posted on this forum so UTFSE.

If that fails the Wiley SE will find it. The chlorination is under UV in CCl4, and the product is a solid.

It is a useful replacement for COCl2 that works most of the time. Diphosgene (trichloromethyl chloroformate) is more reactive but not quite as safe.

Do not make or use either outside of a hood.
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[*] posted on 8-2-2018 at 03:22


Wikipedia says triiphosgene needs phosgene to begin with. So, why work with triiphosgene?
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[*] posted on 8-2-2018 at 07:20


The place, where triphosgene is made need not be the place where the triphosgene is used. Handling triphosgene is much easier and less risky than handling phosgene (albeit still quite risky and not something for the starting kitchen-chemist).

Btw, where does Wikipedia say that triphosgene needs phosgene to begin with? I do not read that on the wiki-page. It apparently is made from dimethylcarbonate and chlorine, by completely chlorinating the methyl groups of this ester.




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[*] posted on 8-2-2018 at 12:26


any time I've ever been exposed to phosgene, it's smelled like the bottom of an old lawn mower- nothing "fresh" about it.



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[*] posted on 8-2-2018 at 14:28


I've always thought phosgene smelled like rotten grass, not fresh grass.

But I only got small whiffs, as I've only handled it inside a strong fume hood. Schlenkware from then on, so no further smell.




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[*] posted on 8-2-2018 at 15:19


Triphosgene is made from dimethylcarbonate yes.
CH3OCO2CH3 + 6 Cl2 → CCl3OCO2CCl3 + 6 HCl

But dimethylcarbonate is made from phosgene.
COCl2 + 2 CH3OH → CH3OCO2CH3 + 2 HCl

So i suppose an amateur could prepare and use triphosgene from dimethylcarbonate if they were able to aquire dimethylcarbonate without making it themselves, or making it without phosgene.
However, the statement about triphosgene being less dangerous or more easy to handle than phosgene seems incorrect by my assessment.

Triphosgene decomposes to phosgene by heat or hydrolysis.
OP, what is it you are intending to do with triphosgene?
or is this purely theoretical.
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[*] posted on 8-2-2018 at 15:38


This is an old thread resurrected for some reason by e14. Check the post history and determine how serious the line of enquiry is.



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[*] posted on 8-2-2018 at 18:23


As wiki correctly states, nobody's producing the DMC via phosgene route nowadays, except some small scale production, isotopes, etc.
Triphosgene is at least order of magnitude safer to work with due to the fact it has some vapor pressure of phosgene above the solid's surface instead of being a pure phosgene.
My experience without fumehood tells me that i could keep the maximum concentration for a gas near the system below 5 ppm, while for a solid-liquid 1-2 ppm is possible. E.g. I made a distillation of elemental bromine without a need for ventilation, approx 1-2 ppm concentration of bromine could be detected near the device.
Thus, triphosgene places this technique close to the edge of safe handling (I'd say not more than 10-20 minutes of exposure allowed in a few days, even without odor sensible), while the use of phosgene gas is completely unacceptable (suicidal).
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[*] posted on 8-2-2018 at 18:40


1 L of DMC for $30 on Amazon:
https://www.amazon.com/MG-Chemicals-Dimethyl-Carbonate-Metal...
Bit pricey in my opinion, but for such an exotic chemical it isn't bad.




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[*] posted on 11-2-2018 at 15:51


Huh. Dimethyl carbonate has always been elusive for me. Interesting to see it on Amazon. I've wanted to attempt my bromide-catalyzed chlorination reaction with this stuff, but never had the requisite safety equipment.

I've never smelled phosgene, but it certainly can't be good for you:





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