Sciencemadness Discussion Board - OTC Oxalyl Chloride Challenge

OTC Oxalyl Chloride Challenge

JJay - 20-5-2017 at 13:17

I think we can all agree that oxalyl chloride is an interesting and useful reagent. It's not that hard to make, but most of the readily accessible syntheses require using phosphorus. While phosphorus is a chemical within reach of many amateurs, it is even harder to obtain than oxalyl chloride, and it cannot be obtained in all jurisdictions. For this reason, as well as other reasons, it would benefit many amateurs to have a working synthesis for oxalyl chloride that does not require any phosphorus compounds. Obviously, it would also be best to avoid using chlorinating agents like thionyl chloride unless they can be generated from readily available chemicals.

So I'm tossing around the idea of running a contest around finding a workable amateur synthesis for oxalyl chloride. An ideal synthesis would involve the use of only OTC compounds, but it would be more or less equally desirable to have one using only common reagents can be easily obtained online. I'm not really sure what I can offer for a prize for this challenge... the only rare and exotic chemical I have in quantity is sodium ethyl sulfate monohydrate... perhaps a small quartz distillation flask would be a suitable trophy?

What would be a suitable prize for such a challenge?

Sulaiman - 20-5-2017 at 15:08

I guess that you will have to specify "OTC" first,
e.g. I buy almost everything, other than food, online,
does mail-order available to the public count ?
Or, if you're going for 'clandestine', cash-only sales ?

by region;
e.g. here in UK I am allowed red phosphorous, oxalyl chloride and thionyl chloride^*,
but not oxalic acid >10% w/w

other members cannot legally purchase sulphuric acid, etc.

so, I for example should have little difficulty in obtaining whatever starting reagents are the most convenient,
whilst others may have to boil-dowm battery acid, do a non-trivial plant extraction ..... etc.

not a level playing field.

^* provided that I produce less than 30 tonnes per year, which would make it a Schdule 3 substance under the Chemical Weapons Convention

[Edited on 20-5-2017 by Sulaiman]

Texium - 20-5-2017 at 15:19

I would disagree that phosphorus is "even harder to obtain" than oxalyl chloride, as I own phosphorus that I was able to easily purchase online, while I have not been able to find a source of oxalyl chloride that is available to amateurs (as in it's only for sale from companies like Sigma and Acros). It's a shame, I've been wanting to make some TCPO. Making PCl5 seems like such a hassle.

Crowfjord - 20-5-2017 at 15:36

Elemental Scientific sells it as a special order chemical. Or did they go out of business? Doesn't look like the site has updated since November, and I don't recall Tom having posted for a while.

Texium - 20-5-2017 at 15:40

They haven't gone out of business, but they haven't done special orders in a long time. The things on the current list have been out of stock ever since the last time he organized one.

clearly_not_atara - 20-5-2017 at 16:05

I suggest using SCl4.

This species is generated by the reaction of sulfur with two equivalents of liquid chlorine. It decomposes to SCl2 and Cl2 above -30 C. Hydrolysis is very exothermic; it might be possible to make SOCl2 this way, but I know of no successful report. It reacts with AlCl3 to give trichlorosulfonium tetrachloroaluminate which is stable to somewhat higher temperatures but most refs about SCl3AlCl4 are in German.

The challenge is to find a way to dissolve oxalate salts at those temperatures and a solvent you can do it in. The best approach looks like an ionic liquid or deep eutectic solvent where neither component will react with SCl4, and particularly the case where one of the components is a metal halide seems interesting. I believe CrCl3/tetramethylammonium chloride or CrCl3/dimethylimidazolium chloride is a candidate solvent here.

So my suggestion is the reaction of oxalate salts with SCl4 or a stabilized derivative in an ionic liquid comprising a metal chloride and a quaternary ammonium chloride.

gdflp - 20-5-2017 at 16:09

Understandable, really. It seemed like a hassle for them and I can't imagine there was ever a huge demand.

They've always been very helpful when I've spoken to them though, so I'm sure they'd be more than willing to help if you contacted them directly.

j_sum1 - 20-5-2017 at 16:12

When did gdflp become super moderator? Congratulations.

[Edited on 21-5-2017 by j_sum1]

Assured Fish - 20-5-2017 at 18:54

Well since TCT (cyanuric chloride) can chlorinate oxalic acid to oxalyl chloride, i would imagine this would be the most OTCish way to go about preparing your oxalyl chloride.
Of coarse preparation of cyanuric chloride is not something to be taken lightly. Typically its prepared by trimerization of cyanogen chloride over a catalyst. Cyanogen chloride could be prepared by carefully adding an aqueous solution of sodium cyanide to an aqueous solution of chlorine at a low temp, followed by a rather frightening low temperature distillation and drying.

I can see no reason why all of this could not be achieved by a determined chemist with a good quality respirator working outside or in a fume hood although im not evoking anyone to try.
Personally if i were going to attempt something like this id rather work with cyanogen bromide given the higher BP and lower volatility.

Everything required to do such a preparation could be bought over the counter: TCCA, oxalic acid, HCl etc. My only exception would be for the trimerization catalyst to which i have no idea what sort of carbon catalyst we would require here, i have not been able to find much information on it although i haven't tried very hard, but typically trimerization of alkenes is accomplished using a catalyst such as palladium on carbon Pd/C.
I did find this but i don't have access to it:
http://onlinelibrary.wiley.com/doi/10.1002/14356007.a08_191/...

JJay - 20-5-2017 at 19:10

I should clarify that routes involving phosgene are disallowed, even if you make it yourself. Chemicals available by mail order to the public can be used within reason, but it must be possible to carry out your synthesis without purchasing any chemicals from clandestine sources or chemical suppliers. So bleaching powder, permanganate, nitric acid, etc. are fine, but alkali metals and borohydride are borderline. Building blocks are out, as are all exotic reagents typically only used by professional chemists, unless they can be made by amateurs. Chemicals available from soapmaking companies, pottery suppliers, pyro suppliers, nuclear hobby companies, biodiesel supply, flavoring manufacturers, Asian distributors, etc. are fair game.

You can make oxalic acid from OTC materials if necessary, but this is not required. I would like to be as fair as possible, but the aim of this challenge is to discover a working route to produce oxalyl chloride, and this may not be possible or legal everywhere, and it is solely your responsibility to ensure that you have whatever licenses or authorizations you may require to attempt the challenge or win the prize. Obviously, a fully OTC synthesis of oxalyl chloride using only simple beakers would be what is most desired, but online purchases and sophisticated equipment are permitted.

The prize will be a quartz distillation flask, with judging to take place on September 1. It will be delivered to whatever address you specify, anywhere in the world, by parcel post. To win the challenge, you must actually produce some oxalyl chloride using your proposed synthesis.

[Edited on 21-5-2017 by JJay]

JnPS - 21-5-2017 at 14:38

Already looking up old patents and bugging professors for copies of ancient ACS articles, I'll be on vacation for a little over a week, but once I get back, this will be a fun way to start off my summer break. Thanks for the challenge JJay!

Sulaiman - 21-5-2017 at 15:16

Just in case anyone interested missed this thread http://www.sciencemadness.org/talk/viewthread.php?tid=8742

Melgar - 21-5-2017 at 20:18

Oxalic acid should be accessible by carefully adding potassium permanganate to ethylene glycol. Manganese will then form a water-soluble oxalate salt with it, which spares you the annoyance of having to deal with MnO2 crud. It's also a nice visual indicator of the reaction progress. This most likely oxidizes quite a lot to CO2 as well, but at least antifreeze is pretty cheap.

theAngryLittleBunny - 21-5-2017 at 20:47

Quote: Originally posted by Melgar

Oxalic acid should be accessible by carefully adding potassium permanganate to ethylene glycol. Manganese will then form a water-soluble oxalate salt with it, which spares you the annoyance of having to deal with MnO2 crud. It's also a nice visual indicator of the reaction progress. This most likely oxidizes quite a lot to CO2 as well, but at least antifreeze is pretty cheap.

But potassium permanganate isn't cheap, you need to take 8 elecrons from an ethylen glycol in order to turn it into oxalic acid one KMnO4 takes 5 electrons if the MnO2 oxidizes as well, so you need 1.66 KMnO4 for every ethylen glycol, which is a ratio of about 25:6 of potassium permanganate to ethylen glycol, so your problem won't be the antifreeze. I think a much better methode would nitric acud + cane sugar, like nile red did.

Melgar - 21-5-2017 at 21:17

Quote: Originally posted by theAngryLittleBunny

Where I am, nitric acid isn't cheap or easy at all, and separating all that is a big mess. My thought was just to go with stuff that most people would have on hand, and would have an easy workup. If you want to go even cheaper though, then how about chlorine bleach and antifreeze? No need to waste nitric acid.

Also, what do you think the yield is oxidizing cane sugar to oxalic acid? Far more of that carbon is going to be oxidized to CO2 than oxalic acid. For an easy workup, you'd probably want to overdo it on the nitric acid, so you could evaporate the residue, which I don't recommend doing if there's anything metal in the vicinity.

Incidentally, the next time someone cites a Youtuber as though they were the one who discovered a particular reaction, I think I'm going to punch whoever happens to be next to me at the time. I'm not sure why it annoys me so much, but it does.

clearly_not_atara - 21-5-2017 at 22:41

KMnO4 cleaves most diols. Won't it also cleave ethylene glycol? CrO3 et al seem better.

It might also be possible to oxidize ethylene glycol with only chlorine. Products however may include phosgene.

j_sum1 - 21-5-2017 at 22:43

I promised myself I would get involved with the next challenge. But this one is out of my league for the moment. And besides I have no need for oxalyl chloride. I love the idea of a challenge though. It's been a while since we had one and even longer since we had one that had a high participation level.

I thought oxalic acid was pretty readily available in most places. If you can't get it then you would want a way of making it at reasonable purity at reasonable volume with minimal time and expense. And I guess that does depend a lot on what is available where you live. To my thinking, nitric acid and cane sugar is a more accessible route than propylene glycol and permanganate. But both seem a waste of reagents. I am not sure what the other options are.

@Melgar
I don't share your dislike for YT citations. I think there is a place for them. Obviously I would not use them for a scientific paper. But in the realm of amateur chemistry they serve as a good way to cite a procedure. Ours is a pretty visual science and a lot can be learned by watching actual practice. If someone wished to investigate the production of OA from sucrose, NileRed's video is not a particularly bad place to start. Of course it is not going to give the depth of a literature survey. But in this case the goal seems to be to get hold of a starting reagent. In that case, depth is not really required. But a working procedure is. 15 minutes watching a video is going to get me that quicker than trawling through a pile of scientific papers or patents.

Melgar - 22-5-2017 at 00:56

Quote: Originally posted by clearly_not_atara

KMnO4 cleaves most diols. Won't it also cleave ethylene glycol? CrO3 et al seem better.

It might also be possible to oxidize ethylene glycol with only chlorine. Products however may include phosgene.

Oh, oxalic acid is definitely not stable in the presence of KMnO4, however by that point you typically have MnO2, not KMnO4. And even that will oxidize oxalic acid, reducing itself to the +2 oxidation state. It's not a particularly practical reaction, but it is a pretty cool one to watch, I have to say. In this sort of competition, you just have to prove a reaction works and is OTC, no?

As far as oxidizing ethylene glycol with chlorine, I believe you're thinking of the similar reaction between benzyl alcohol and chlorine, no? However I think benzyl alcohol is a special case, and most alcohols don't do that. However, I'm not 100% sure on this one.

Quote: Originally posted by j_sum1

@Melgar
I don't share your dislike for YT citations. I think there is a place for them. Obviously I would not use them for a scientific paper. But in the realm of amateur chemistry they serve as a good way to cite a procedure. Ours is a pretty visual science and a lot can be learned by watching actual practice. If someone wished to investigate the production of OA from sucrose, NileRed's video is not a particularly bad place to start. Of course it is not going to give the depth of a literature survey. But in this case the goal seems to be to get hold of a starting reagent. In that case, depth is not really required. But a working procedure is. 15 minutes watching a video is going to get me that quicker than trawling through a pile of scientific papers or patents.

I think the annoying thing is the fact that I learned all this stuff back before these Youtubers had their videos, so when someone tells me "like NileRed" or "like NurdRage", I've usually read about the procedure already, and for a quick refresher, skimming a paper to the relevant part will be MUCH faster than watching a 15-minute youtube video. In chemistry, there's already a set of named reactions, AND NONE OF THEM INCLUDE THE NAMES "NURDRAGE" OR "NILERED"!!!! Ok, sorry, I needed to get that off of my chest.

[Edited on 5/22/17 by Melgar]

j_sum1 - 22-5-2017 at 01:29

Point taken. It's not like these guys have ownership of the procedures. (Although Nurdrage has developed some novel processes and deserves some credit.) It just ends up being a convenient handle to refrence the information. Too convenient perhaps.

I'll try to be a bit more careful and avoid phrases like "Cody's process". But I do confess that I have learned an awful lot in a short time from YT channels. Given that input it seems a sensible thing to discuss.

Sulaiman - 22-5-2017 at 03:20

As a pure amateur I have to say that YouTube videos have been invaluable to me,
it is so helpful to have an informal medium where tips, tricks, warnings etc can be disseminated,
and to see what should (or may) happen before I try gives me more confidence to try things myself,
YT has generated enough cash for some that they can afford to do stupid or exotic experiments and show me in detail, wonderful.

One semi-negative aspect,
sometimes I have an interrest in a reaction so I watch a few YT vids on it,
often I have learned enough from the vids to not bother doing the reaction myself !

EDIT: it is just like cookery;
. personal tuition to boil an egg
. video for process control
. books with pictures for intermediate level
. textbooks for the initiated
. exotic ancient recipies for the enthusiast
etc.
all are useful

[Edited on 22-5-2017 by Sulaiman]

[Edited on 22-5-2017 by Sulaiman]

Chemetix - 22-5-2017 at 03:38

YT has a long way to go to topple the heavyweights of name reactions, and the H.W.Z. does definitely not need another name attached. Huang - Minlon- youtoober variant number 403 is not something I want to see either. But back to the point... umm why Ox chloride ? I don't seem to get the importance of this one.

byko3y - 22-5-2017 at 03:56

The reason why i don't even try to make videos is because text and few pictures are much more informative than watching a video. 5-20 seconds of video might be needed, but that's more than enough.
Many of those making youtube videos actually fail to ascertain the quality of the product, and some even don't bother with idendification at all. That's the result of focus on making video and not on making a reaction product. For this reason it would be great if someone made some new-age picture- and video-assisted guides on preparatory methods while being guided by a hardcore autistic experimentalist.

JJay - 22-5-2017 at 05:42

Oxalyl chloride is interesting in that it can be used to make glowsticks. Also, it is a mild chlorinating agent, or at least it is more mild than many other chlorinating agents. In addition, it is less regulated than certain other chlorinating agents like thionyl chloride, which have historically been used to make chemical weapons. It raises fewer eyebrows than phosphorus oxychloride/trichloride/pentachloride because it doesn't contain phosphorus. And it's not nearly as dangerous as phosgene.

A clear writeup specifying reaction conditions and yields is probably easier to follow than a YouTube video, but there is something to be said for actually seeing a successful reaction take place. Often, written procedures are vague or simply don't work exactly as described, and it is certainly much easier to watch a 15 minute YouTube video than to spend several hours compiling documents and doing calculations before running several trial experiments to find something that works.

I think a 500 mL quartz distillation flask is a suitable trophy, and I think that home chemists definitely want to know how to make oxalyl chloride using readily available chemicals. That is why I am running this challenge.

Melgar - 22-5-2017 at 07:41

To be fair, I have nothing against the YouTubers themselves, only people who reference procedures from their videos by the YouTuber's name, as opposed to the actual name of the reaction.

theAngryLittleBunny - 22-5-2017 at 08:29

Quote: Originally posted by Melgar

To be fair, I have nothing against the YouTubers themselves, only people who reference procedures from their videos by the YouTuber's name, as opposed to the actual name of the reaction.

The actual name of the reaction, hmm....as far as I know, I don't think there is a name for the oxidation of sugar by nitric acid, but please correct me if I'am wrong. And I didn't know that you're 13 years older then me and therefore probably much more experienced. As others said, I rather like to see the whole procedure, because I generally like to know exactly what to expect before doing it myself. But if you you're more experiwnced, reading a paper is much more efficient.

Melgar - 22-5-2017 at 10:13

Quote: Originally posted by theAngryLittleBunny

Actually, you at least were considerate enough to describe the reaction, so I really shouldn't be complaining in this thread, but some other one. The reaction is pretty ancient though (first recorded in 1745):

https://en.wikipedia.org/wiki/Oxalic_acid#History

I don't fault anyone for learning chemistry from Youtube videos, I'm sure they're helpful for seeing exactly how a reaction is done and how it looks to do it. It just sounds silly to attribute a centuries-old reaction to a Youtuber, at least to me. The only thing that really grates on me is when I'm trying to answer someone's question, and ask something like "well, what reaction did you use to make it?", and they say "the one NileRed used" or something, rather than actually describe the reaction.

However, you are hereby commended for actually describing the reaction as "oxidation of sugar by nitric acid" so that I could tell what you were talking about. My irritation was, in fact, misdirected.

To get the subject back on topic, adding hydrogen peroxide to nitric acid is very helpful for reducing NOx fumes and increasing the useful life of your acid. Also, benzotrichloride is probably the most OTC-accessible reagent I can think of for preparing acyl chlorides. It'd probably work really well for oxalyl chloride too, since oxalyl chloride has a boiling point of like 61˚C, and is easily distilled from a mixture of oxalic acid, benzotrichloride, benzoyl chloride, and benzoic acid.

JJay - 22-5-2017 at 10:21

Whoah, cool, the original reference is in Latin: https://books.google.com/books?id=HcuNbkfxYQMC&pg=PA238#...

clearly_not_atara - 22-5-2017 at 14:48

Yeah, the problem with most chlorinating agents here is that the anhydride of oxalic acid, if produced, decomposes instantly to CO2 + CO, ruining your procedure. I assume this is why PCl5 is preferred over any related reagent: it forms an intermediate phosphate ester, and one equivalent of PCl5 can convert oxalate all the way to oxalyl chloride wothout the intermediacy of HO2CCOCl (oxalyl monochloride), which likely decomposes spontaneously to CO2 + CO + HCl.

SCl4 can chlorinate oxalate fully in one go. Benzotrichloride might work. Phthaloyl chloride, SOCl2, POCl3, TsCl, MeCN*HCl, etc will likely fail and produce gases.

EDIT:

Quote:

Historically oxalic acid was obtained exclusively by using caustics, such as sodium or potassium hydroxide, on sawdust.

[Edited on 22-5-2017 by clearly_not_atara]

Alice - 22-5-2017 at 16:16

Not directly a contribution to this challenge, as it is reported not to work for oxalic acid is the use of SiCl4 to convert carboxylic acids into the corresponding acid chlorides: Silicon tetrachloride as a reagent for the preparation of acid chlorides

Maybe TiCl4 then?

clearly_not_atara - 23-5-2017 at 00:46

I suspect that TiCl4 would react by the same or similar mechanism as SiCl4; particularly, that a second equivalent of TiCl4 must react with the titanium carboxylate in order to generate the acyl chloride, and this occurs with titanium and silicon particularly because they are not very eager double-bond formers, so it does not make sense to draw a mechanism involving Si or Ti with a double bond in it. So in order to release the carboxyl group, the oxygen must have something else to bond to, most likely Ti.

However, in this case the molecular metal carboxylate could react with itself generating oxalyl anhydride (particularly because oxalyl is an ok leaving group) and thus decomposing.

By contrast here is the mechanism I am proposing for SCl4:

although I am not sure of this. Clearly if SOCl2 is used the cyclic intermediate would decompose to SO2 + CO + CO2, right?

But with benzotrichloride you get benzoyl chloroglyoxylate which is fine. I think.

Alice - 23-5-2017 at 05:29

Regarding TiCl4, I think you are right, didn't think about the double bond issue...

Hypothetically Ti(C2O4)2 may form as well as a the mixed compound TiCl2(C2O4) which might give a TiO2 network - or not.

Some hints about the action of TiCl4 on acetic acid can be found here: http://pubs.acs.org/doi/abs/10.1021/ja01490a047 or for benzoic acid: http://onlinelibrary.wiley.com/doi/10.1002/prac.19590080108/...

For SCl4 I would have drawn the same mechanism although not sure if SCl2(C2O4) or SCl(C2O4)⁺ x Cl⁻ or there is an equilibrium anyway.

For SOCl2 I imagine either decomposition occurs on the cyclic intermediate or it survives resulting in the mixed anhydride: HSO3-C2O2-Cl which may further decompose leading to HO-C2O2-Cl and SO2.

Quote:

But with benzotrichloride you get benzoyl chloroglyoxylate which is fine. I think.

Looks good, I wonder if there is a literature procedure for the reaction or similar reactions?

[Edited on 23-5-2017 by Alice]

JJay - 17-6-2017 at 13:34

It's been a while since I posted this, so I figured I would give this thread a bump.

The challenge is most definitely still on. There has been some very interesting and I think fruitful discussion so far. Submissions are due September 1 at midnight in your time zone. Remember, to win the prize you must actually produce some oxalyl chloride. If more than one person successfully produces oxalyl chloride, the easiest and most accessible synthesis will be chosen as the winner.

The prize will be a new flask like this one: http://www.ebay.com/itm/500ml-Customized-Quartz-Distilling-F...

chemplayer... - 25-6-2017 at 22:44

Interesting challenge! We tried directly chlorinating anhydrous oxalic acid with PCl3 and this didn't work, apparently requiring PCl5 to work. So phosphorus-based reagents are not necessarily suitable intermediates anyway.

The only thing we found which could (in limited yield) generate an OTC acid chloride was the reaction of the cold acid amide and acetonitrile together with HCl gas (all under anhydrous conditions of course).

Does oxalylamide (oxalic acid diamide) exist? Could it be produced from oxalic acid and urea? Could this be dissolved in acetonitrile and then dry HCl gas passed in whilst cold for a duration, and the result then distilled (bp ~60C)...

Of course this then requires to get acetonitrile via OTC sources...

Cryolite. - 25-6-2017 at 23:16

Oxamide does in fact exist. It is made industrially by hydrating cyanogen or dehydrating ammonium oxalate. However, I worry that the mono chlorinated intermediate may just decompose or dehydrate, to either CO or cyanogen.

clearly_not_atara - 26-6-2017 at 00:39

Oxamide is produced by the pyrolysis of ammonium oxalate. This is not a high yielding reaction:

4(NH4)2O2CCO2 >> 4 NH3 + CO + CO2 + 2NH2COCO2H + NH2COCONH2 + 5 H2O

Oxamic acid, the other component, dissolves in alkaline water and precipitates with addition of Ca2+ or Ba2+. Oxamide is poorly soluble. Small amounts of hydrogen cyanide are produced.

See "The decomposition of bioxolate of ammonia by heat". In the case where oxamide rather than oxamate is progressively chlorinated I think there is a significantly better chance of success.

[Edited on 26-6-2017 by clearly_not_atara]

[Edited on 26-6-2017 by clearly_not_atara]

JJay - 26-6-2017 at 08:25

Some research on the subject suggests that it is possible to prepare acetonitrile from alanine and TCCA: http://www.sciencemadness.org/talk/viewthread.php?tid=9094#p... Apparently, sodium hypochlorite has a similar action.

I've read that pH can influence whether an aldehyde or a nitrile forms, with alkaline pH leading to nitrile formation. I've also read results that contradict these findings. It has been suggested that concentration of the amino acid matters also. I tried forming aldehydes in very dilute solution this way a while back and never managed to isolate any, but Amos posted NMR results for phenylacetonitrile made with concentrated bleach some months ago: http://www.sciencemadness.org/talk/viewthread.php?tid=32534

It seems reasonable to suppose that acetonitrile could be made by the action of concentrated bleach on alanine.

Melgar - 26-6-2017 at 09:02

Quote: Originally posted by JJay

It seems reasonable to suppose that acetonitrile could be made by the action of concentrated bleach on alanine.

The only annoying part would be sourcing the TEMPO, which is a lot harder to get than acetonitrile.

JJay - 26-6-2017 at 09:43

Quote: Originally posted by Melgar

Quote: Originally posted by JJay

It seems reasonable to suppose that acetonitrile could be made by the action of concentrated bleach on alanine.

The only annoying part would be sourcing the TEMPO, which is a lot harder to get than acetonitrile.

They used TEMPO in the first paper on that thread but not in the others. Also, it was used for an experiment involving benzylamine in DCM to elucidate the mechanism of the reaction; the procedures at the end of the document performed in aqueous base on amino acids do not require TEMPO, nor do the (admittedly lower-yielding) procedures in the half dozen other papers on the subject.

clearly_not_atara - 26-6-2017 at 09:49

The only acetonitrile synth anyone needs is refluxing acetamide over Al2O3 that was washed with phosphoric acid. Acetonitrile distills out (bp 82 C) and can be collected in a condenser.

http://www.sciencemadness.org/talk/viewthread.php?tid=11137&...

JJay - 26-6-2017 at 10:55

I wonder if garden-grade pumice would work instead of alumina. The trick is cooling your reflux column with boiling water.

Maybe you could use a coffee percolator?

fac358b66aa5448fe362c5eb767d745c.jpg - 8kB

fac358b66aa5448fe362c5eb767d745c.jpg - 8kB

JJay - 8-7-2017 at 11:39

Here's a good example of oxalyl chloride in amateur use: Making Glow Sticks

And here's another: Vapor Activated Glow Stick

karlos³ - 8-7-2017 at 13:09

The Anthony-Speeter synthesis of indole glyoxylic amides is another quite interesting application of oxalyl chloride, very easy to do for the amateur and a rewarding experience as well.

Rhodanide - 10-7-2017 at 09:31

Quote: Originally posted by Alice

Maybe TiCl4 then?

Good luck even obtaining TiCl4, I sure tried... and failed. If you find any, it's probably somewhere where it can't *legally* be removed.

clearly_not_atara - 10-7-2017 at 18:49

I was thinking about other esters that could be converted to the chloride -- maybe try radical chlorination of dibenzyl oxalate? If I had to guess, I'd say that 1,6-diphenyl-1,1,6,6-tetrachloro-2,5-dioxa-3,4-dioxohexane should decompose to oxalyl chloride and benzoyl chloride, as long as the intermediate products don't decompose first.

Maybe ethylene oxalate could be perchlorinated somehow... pyrolysis might give two equivalents of oxalyl chloride if you're lucky.

JJay - 10-7-2017 at 18:58

I'm surprised no one has suggested antimony pentachloride.

Edit: I just found this thread, where Nicoderm stated that won't work: http://www.sciencemadness.org/talk/viewthread.php?tid=11989

[Edited on 11-7-2017 by JJay]

alternate synthesis

fumingjohnny - 12-7-2017 at 02:55

1. Thionyl chloride can be easily prepared by the action of dichlorine monoxide on elemental sulphur at -12 degree celcius(salt-ice bath can cool down to -20). The thionyl chloride formed is excellent in converting oxalic acid to oxalyl chlorides. Dichlorine monoxide can be made by passing chlorine over mercuric oxide or sodium carbonate.
2. You may want to try treating silicon with chlorine to form silicon tetrachloride and then reacting oxalic acid with SiCl4 to form SiO2 and HCl and Oxalyl chloride.

3.

fumingjohnny - 12-7-2017 at 04:02

3. chlorination of diethyl oxalate.....(CH3CHCl)2(COO)2 and subsequent heating will disproportionate it into acetaldehyde and oxalyl chloride. The oxalyl chloride is immediately distilled off using a water bath.
4. Reaction of Triphenylphosphine with Carbon tetrachloride and oxalic acid should yield oxalyl chloride, triphenylphosphine oxide and chloroform. (please try it and let me know the results)

fumingjohnny - 12-7-2017 at 07:06

5. Sulfuryl chloride SO2Cl2 is used for chlorinating calcium salts of carboxylic acids to form acid chlorides and calcium sulphate. If anyone here has access to sulfuryl chloride then try reacting it with calcium oxalate. The products should be calcium sulphate and oxalyl chloride.
P.S: please post the results.

woelen - 12-7-2017 at 07:23

@fumingjohnny: It is best to put everything in a single post. These three posts can be left as they are now, but if you post again, we would like to have everything combined in a single post.

JJay - 12-7-2017 at 10:21

Quote: Originally posted by fumingjohnny

1. Thionyl chloride can be easily prepared by the action of dichlorine monoxide on elemental sulphur at -12 degree celcius(salt-ice bath can cool down to -20). The thionyl chloride formed is excellent in converting oxalic acid to oxalyl chlorides. Dichlorine monoxide can be made by passing chlorine over mercuric oxide or sodium carbonate.
2. You may want to try treating silicon with chlorine to form silicon tetrachloride and then reacting oxalic acid with SiCl4 to form SiO2 and HCl and Oxalyl chloride.

I don't know how easy that is in practice.... It is theoretically possible to make thionyl chloride by cracking sodium bisulfate to prepare oleum and reacting the oleum with sulfur dichloride, but this requires high temperatures and is quite toxic and extremely smelly. The purification method suggested in Small Scale Synthesis of Laboratory Chemicals is to distill the thionyl chloride from quinoline and linseed oil. This is all conceivably OTC (except for the quinoline, but you might find a substitute or manage to get through intermediate steps with an impure product and purify later), but thionyl chloride can't be used to chlorinate oxalic acid directly... which doesn't necessarily mean that there's no way to do it.

It is said that silicon tetrachloride can't be used for a direct chlorination either, but again, that doesn't mean it's impossible to use it in some sort of chlorination. It's theoretically available OTC.

I'm very curious about benzotrichloride. Free radical chlorination of toluene is about as OTC as it gets.

[Edited on 12-7-2017 by JJay]

clearly_not_atara - 12-7-2017 at 11:13

I think sulfur tetrachloride with liquid chlorine is already easier than using hella-nasty and explosive Cl2O. The downside of course is that SCl4 is unstable above -30 (need dry ice) and it's gonna be tough to solvate oxalic acid at that temperature.

http://en.wikipedia.org/wiki/Dichlorine_monoxide#Explosive_p...

[Edited on 12-7-2017 by clearly_not_atara]

JJay - 12-7-2017 at 11:56

Making sulfur tetrachloride probably requires handling liquid chlorine, but how hard can it be to condense chlorine gas with dry ice?

Tellurium - 12-7-2017 at 23:40

I once condensed chlorine using a bath of dry ice and acetone, it worked out quite well, but I was somewhat scared to accidentally drop the tube full of liquid chlorine

fumingjohnny - 13-7-2017 at 00:28

Got it @woelen
give option no. 3,4,5 a try.
Cl2O is only explosive at higher concentrations. for lower yields of SOCl2 it may be used.

JJay - 13-7-2017 at 01:06

I don't know what to think about #3, chlorination of diethyl oxalate. It's pretty easy to do a Fischer esterification of oxalic acid with ethanol, right? Then what?

#4 requires use of phosphorus compounds, which are not permitted. But it occurred to me today that you could conceivably ignite a calcium phosphate thermite and then chlorinate the slag in a 250 C oven to make phosphorus pentachloride and chlorinate the oxalyl chloride with it. It is even possible to do it purely OTC, although I imagine it could be hard to set off calcium phosphate thermite made by heating chicken bones in a crucible and grinding aluminum foil in a coffee grinder.

I'm not sure what to think about #5, but I remember seeing a writeup recently on an experiment that obtained sulfuryl chloride as a significant byproduct....

[Edited on 13-7-2017 by JJay]

plastics - 13-7-2017 at 03:45

Quote: Originally posted by JJay

I don't know what to think about #3, chlorination of diethyl oxalate. It's pretty easy to do a Fischer esterification of oxalic acid with ethanol, right? Then what?

#4 requires use of phosphorus compounds, which are not permitted. But it occurred to me today that you could conceivably ignite a calcium phosphate thermite and then chlorinate the slag in a 250 C oven to make phosphorus pentachloride and chlorinate the oxalyl chloride with it. It is even possible to do it purely OTC, although I imagine it could be hard to set off calcium phosphate thermite made by heating chicken bones in a crucible and grinding aluminum foil in a coffee grinder.

I'm not sure what to think about #5, but I remember seeing a writeup recently on an experiment that obtained sulfuryl chloride as a significant byproduct....

[Edited on 13-7-2017 by JJay]

Only patents I know, curious nonetheless

Attachment: TetrachloroethyleneOxalate.pdf (204kB)
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Attachment: OxalylChloride.pdf (209kB)
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clearly_not_atara - 13-7-2017 at 11:46

I suggest using iron phosphate with titanium metal since the corresponding phosphides are much less prone to hydrolysis and do not release phosphine.

JJay - 13-7-2017 at 12:08

I think iron phosphide can be purchased also. I do assume that if you have measures in place to deal with chlorine fumes, you can also deal with a little phosphine, but it is worth mentioning that all traces of water should be kept away from calcium and aluminum phosphides, and people should only attempt to work with them if they understand what they're getting into.

[Edited on 13-7-2017 by JJay]

fumingjohnny - 13-7-2017 at 22:12

Sulfuryl chloride SO2Cl2 is prepared by the reaction of sulphur dioxide and chlorine in the presence of activated charcoal or camphor catalyst. If small quantities can be prepared by anyone having a reasonably good lab then it may be tested against oxalic acid to confirm the formation of oxalyl chloride.
P.S If you never try youl'll never know.......My lab is not good enough to make these compounds.
somebody give it a go and spread the word on the results.

fumingjohnny - 13-7-2017 at 22:21

sorry.....not oxalic acid but calcium oxalate +sulfuryl chloride

JJay - 30-8-2017 at 20:40

Hello everyone. I think some great information has been compiled here. I know I've certainly learned a lot about chlorinating agents while researching possible routes to oxalyl chloride. But the challenge won't be a complete success unless someone actually synthesizes some oxalyl chloride. The challenge deadline is still September 1, midnight in your time zone (so you can spend all day on September 1 on your entry if you like) although I could extend it if anyone is close and needs more time.

Please post here or contact me by U2U for further instructions if you intend to submit an entry for the prize. Good luck!!

Melgar - 30-8-2017 at 21:19

I may actually give it a shot. I'm only missing one chemical, and have large excesses of the others. If I can find the one for sale that I'm looking for, then sure. But I only can test one specific theoretical synthesis, and if it doesn't work, I've got nothing.

XeonTheMGPony - 31-8-2017 at 07:56

Quote: Originally posted by byko3y

The reason why i don't even try to make videos is because text and few pictures are much more informative than watching a video. 5-20 seconds of video might be needed, but that's more than enough.
Many of those making youtube videos actually fail to ascertain the quality of the product, and some even don't bother with idendification at all. That's the result of focus on making video and not on making a reaction product. For this reason it would be great if someone made some new-age picture- and video-assisted guides on preparatory methods while being guided by a hardcore autistic experimentalist.

That's what I plan to do some point, I'll be starting on core lab techniques as I notice not allot of use full treaties on say proper distillation methods where they get to all the 5 W's and on why you do what is don.

Then start on the making of use full lab solvents, Ethanol/Chloroform/Acetic Acid and GAA, so on.

But that thing called life eats allot of my time!

XeonTheMGPony - 31-8-2017 at 08:23

Quote: Originally posted by fumingjohnny

Sulfuryl chloride SO2Cl2 is prepared by the reaction of sulphur dioxide and chlorine in the presence of activated charcoal or camphor catalyst. If small quantities can be prepared by anyone having a reasonably good lab then it may be tested against oxalic acid to confirm the formation of oxalyl chloride.
P.S If you never try youl'll never know.......My lab is not good enough to make these compounds.
somebody give it a go and spread the word on the results.

Can you provide names for these reactions or the reaction conditions, as I am adept at doing gas phase reactions!, mind you still rebuilding/building my lab.

clearly_not_atara - 31-8-2017 at 10:34

Sulfuryl chloride will not work for this reaction, so it doesn't matter.

Melgar: What route? Benzotrichloride?

JJay: bit silly to end the contest with no entries don't you think?

[Edited on 31-8-2017 by clearly_not_atara]

JJay - 31-8-2017 at 11:01

Well, I can't extend the deadline forever, but I can push it back 1-2 weeks if someone is working on an entry and needs more time.

Geocachmaster - 31-8-2017 at 17:22

I made a good plan that started with 100% hardware store chemicals, I'm 60-70% sure that it would work. Only a few steps too. Unfortunately I would probably need at least a full week (all day everyday) of experimenting to get it working and I am very short on time. Maybe if I devoted all of my free time from now on I could do it by October but I've got a bunch of other projects to do too. I won't be able to enter the competition, but maybe sometime later (IDK December?) I'll post about it. Sorry for being cryptic but I think it's a very good idea and I don't want to give it away or embarrass myself if it doesn't work.

Melgar - 2-9-2017 at 02:41

Quote: Originally posted by clearly_not_atara

Melgar: What route? Benzotrichloride?

Yes. Toluene hasn't been easy to find, although I'm pretty sure there are auto body shops nearby that would sell it. I called up a Sherwin-Williams in Manhattan, but apparently the closest one to me that carries any is on the far side of the Bronx. I guess I'll have to call up auto body shops again today.

If I'm going to be gassing all the way to benzotrichloride, I'd need to do a much better job than usual of drying the chlorine going into it, as well as scrubbing the off-gases. Sodium sulfite solution (NaOH + metabisulfite) should get HCl and Cl2, right? I'd probably use like 90% NaOH and 10% metabisulfite.

By the way, how hard is it usually to get dry ice? There's one place in Manhattan that sells it for sure, but I feel like it has to be more common. I don't think I've ever seen it advertised though.

Crowfjord - 2-9-2017 at 05:59

Dry ice accessibility is kind of touch and go. It's not usually advertised but some grocery stores will sell it, they will have a cooler in the open under lock and key. Sometimes hardware stores will sell it in areas where hunting and fishing are popular. Barring those, you might try an ice cream place like Baskin Robins, or ask a vendor that sells that super-cold "future" ice cream, Dippin Dots.

zed - 2-9-2017 at 12:52

Here in Portland, the local supermarkets carry dry ice. Fred Meyer has it. About $1.50 per pound.

As for Toluene, our local auto-parts stores (Shucks/O'Reilly) sell it for about $25.00 per gallon.

Kinda spendy if you ask me, but alas, I didn't make the world as it is....and I can't make it cheaper.

TheNerdyFarmer - 4-9-2017 at 16:12

So, I have seen that this challenge has been postponed. What is the new ending date of this now?

JJay - 4-9-2017 at 17:13

I'm pretty sure the prize is off the table at this point. If someone feels this is unfair to him/her personally, we can talk about it, but I'm not convinced that postponing even two weeks would generate any oxalyl chloride, and I'd like to try to make some. So let's say that if you make some oxalyl chloride before I do, feel free to hit me up.

boilingstone - 25-8-2018 at 13:13

Ozonolysis of acetylenes can give the diketone, among other products. As awful an idea attempting an ozonolysis of dichloroacetylene is, could something like that work? How does dibromoacetylene compare to dichloroacetylene, and would oxalyl bromide be just as useful?

This prepchem page describes a simple synthesis of dibromoacetylene from 1,1,2-tribromoethylene at least.
http://www.prepchem.com/synthesis-of-dibromoacetylene/

Edit:
Here's my brainstorm,

1. Pass acetylene through dry bromine to yield tetrabromoethane
http://www.sciencemadness.org/talk/viewthread.php?tid=24781
2. React with a base to yield 1,1,2-tribromoethylene

3. Follow Prepchem procedure linked above to yield dibromoacetylene

4. Ozonolysis(?) to yield oxalyl bromide

The War Gases Chemistry and Analysis, by M. Sartory, 51, 1939 has a good section on acetylene halides (pg. 57) and oxalyl halides (pg. 66), but doesn't mention synthesizing one from the other. Interestingly, the acetylene halides are ranked in stability from I>Br>Cl, where as the oxalyl halides are ranked in stability from Cl>Br>I. Working with the bromides might be a happy medium, in a very loose sense of the word "happy".

Attachment: The War Gases Chemistry and Analysis.pdf (4.1MB)
This file has been downloaded 648 times

[Edited on 25-8-2018 by boilingstone]

JJay - 26-8-2018 at 05:43

For people reading this thread, the challenge is back up: https://www.sciencemadness.org/whisper/viewthread.php?tid=82...

boilingstone:

I have no idea if your proposed route would work. Ozone would not be the first oxidizer I would think of for that oxidation... why ozone?

clearly_not_atara - 26-8-2018 at 13:40

If chloroacetyl chloride is available, this might be converted to a thioglycolic thioester by rxn with eg thiophenol. That can become an oxalic dithioester by rxn with SeO2 if the Riley oxidation works on such a substrate. Sulfuryl chloride can convert some thioesters to the acyl chlorides as illustrated by the conversion of monothiocarbonates to chloroformates:

https://www.google.com/amp/s/www.researchgate.net/publicatio...

boilingstone - 27-8-2018 at 01:47

Taken straight from wikipedia:

"Ozonolysis of alkynes generally gives an acid anhydride or diketone product, not complete fragmentation as for alkenes. A reducing agent is not needed for these reactions. The exact mechanism is not completely known."

If in this reaction, R = halogen is in scope, then ozonolysis of the dihaloacetylene should yield the oxalyl halide.

I have a paper on the ozonolysis of acetylenes if anyone is interested

[Edited on 27-8-2018 by boilingstone]

JJay - 27-8-2018 at 03:49

Quote: Originally posted by boilingstone

Taken straight from wikipedia:

"Ozonolysis of alkynes generally gives an acid anhydride or diketone product, not complete fragmentation as for alkenes. A reducing agent is not needed for these reactions. The exact mechanism is not completely known."

If in this reaction, R = halogen is in scope, then ozonolysis of the dihaloacetylene should yield the oxalyl halide.

I have a paper on the ozonolysis of acetylenes if anyone is interested

[Edited on 27-8-2018 by boilingstone]

I am interested. I'm looking at a few proposed mechanisms for the reaction (it is typically performed at dry ice temperatures with non-halogenated alkynes), and they don't show what happens to the singlet oxygen radicals... apparently, peroxide polymers can be produced as a byproduct. I bet the workup is exciting.

Potassium permanganate can similarly oxidize alkynes to diketones, and the reaction can be performed at room temperature in DCM... at least for alkynes where R and R' are carbon chains.

Dichloroacetylene can probably be prepared from tetrachloroethene, either by reducing it directly to dichloroethyne or reducing it to trichloroethene and dehydrohalogenating it with a strong base.

[Edited on 27-8-2018 by JJay]

boilingstone - 27-8-2018 at 08:42

From what I've read about dichloroacetylene, I would have to strongly advise against its synthesis. According to wikipedia (again) dichloroacetylene is extremely toxic, pyrophoric, and may detonate at its boiling point. It seems there is a good reason it was mentioned in "The War Gasses...".

While dibromoacetylene suffers from similar issues, apparently these issues are less severe.

again, reference "The War Gasses..." I posted last time for more info

AJKOER - 27-8-2018 at 08:57

First, one may wish to investigate a claim of a successful photochlorination path to (COCl)2, which has been previously presented on SM, see http://www.sciencemadness.org/talk/viewthread.php?tid=8291 ..
------------------------------------------

Found a photolysis path reported in the literature (see p. 23 to 24 at https://books.google.com/books?id=nxkHzjcjMe0C&pg=PA23&a... . However, the methods employs ethylene carbonate, a phosgene equivalent. The reaction takes place at 70-100 C in the presence of chlorine (no solvent) and an initiator using a high-pressure Hg lamp. Interestingly, since (CH2O)2CO is classified as the carbonate ester of ethylene glycol and carbonic acid, this prep is related to the previous procedure.
--------------------------------------------

Next idea, less toxic but much more speculative. Those acquainted with photolysis may remember how hydrogen and chlorine can be easily radicalized with light at low temperatures. In the current case, we need to radicalize only some of the chlorine via photochlorination (see general reaction mechanics outlined in Wikipedia at https://en.wikipedia.org/wiki/Photochlorination ). An important comment per Wikipedia, is, to quote:

“The selectivity of photochlorination (with regard to substitution of primary, secondary or tertiary hydrogens) can be controlled by the interaction of the chlorine radical with the solvent, such as benzene, tert-butylbenzene or carbon disulfide.[14] The complex formation between benzene and the chloride radical reduces its reactivity which increases the selectivity.[15] By varying the solvent the ratio of primary to secondary hydrogens can be tailored to ratios between 1: 3 to 1: 31.[16] At higher temperatures, the reaction rates of primary, secondary and tertiary hydrogen atoms equallize. Therefore, photochlorination is usually carried out at lower temperatures.[13)“

So, an attempt at photolysis would be to apply light in the presence of dry chlorine and dry oxalic acid in an appropriate solvent (per above or none, just use less efficient gaseous nitrogen, since the net reaction implies only half of the Cl2 should be radicalized, I would try to avoid over radicalization of the chlorine with a possible loss of yield). One of many speculated schemes includes:

Cl2 + hv → •Cl + •Cl

H2C2O4 + •Cl → HCl + •HC2O4

•HC2O4 + Cl2→ HCl + •C2O4Cl

•C2O4Cl + •Cl → (COCl)2 + O2 or, possibly unsuccessfully, 2 CO + Cl2 + O2

[ or, possibly as well:

•C2O4Cl + Cl2 → (COCl)2 + •Cl or, possibly unsuccessfully, 2 CO + Cl2 + •Cl ]

With an implied net:

2 Cl2 + H2C2O4 + hv → 2 HCl + O2 + (COCl)2

Note, my speculation on a key problematic reaction:

•HC2O4 + •Cl→ HCl + 2 CO2

Hence, my suspected need to limit the relative creation of •Cl to remaining Cl2.
-------------------

The literature also cites the use of atomic chlorine on aqueous H2C2O4 and FeCl3, which I claim is different from the dry acid (no H+ + C2O4(2-) ions, see https://cdn-pubs.acs.org/doi/10.1021/ja01208a024 ) producing only CO2 and HCl.

[Edited on 27-8-2018 by AJKOER]

Metacelsus - 27-8-2018 at 09:21

I strongly advise against the synthesis of dichloroacetylene. We had an incident a few months ago in my university lab when a graduate student was a bit sloppy with a reaction, and dichloroacetylene was produced as a byproduct. It immediately exploded. Luckily, nobody was hurt, since the reaction was on a small scale.

Anyway, intentionally trying to produce dichloracetylene is extremely dangerous. Reacting it with ozone would be sheer insanity.

JJay - 27-8-2018 at 11:24

Trichloroethene acts as a stabilizer for dichloroacetylene, but I am pretty sure it forms phosgene under ozonolysis or permanganate oxidation.

mackolol - 27-8-2018 at 12:19

Quote: Originally posted by AJKOER

First, one may wish to investigate a claim of a successful photochlorination path to (COCl)2, which has been previously presented on SM, see http://www.sciencemadness.org/talk/viewthread.php?tid=8291 ..
------------------------------------------

So, an attempt at photolysis would be to apply light in the presence of dry chlorine and dry oxalic acid in an appropriate solvent (per above or none, just use less efficient gaseous nitrogen, since the net reaction implies only half of the Cl2 should be radicalized, I would try to avoid over radicalization of the chlorine with a possible loss of yield).

But chlorine decomposes oxalic acid to CO2 CO and HCl. Doesn't it?

AJKOER - 27-8-2018 at 12:47

My prep avoids water as the targeted product (COCl)2 is also water sensitive.

Per this source: "A dictionary of chemistry and the allied branches of other sciences", Volume 4, by Henry Watts, page 250.
Link: http://books.google.com/books?pg=PA250&id=lYXPAAAAMAAJ#v...

"Chlorine does not act on dry oxalic acid; but in presence of water, decomposition quickly takes place, thus:

H2C2O4 + Cl2 = 2CO2 + 2HCl

A similar reaction is produced by bromine, hypochlorous acid, and the chlorides of easily reducible metals. Hence oxalic acid precipitates metallic gold from auric chloride, especially on boiling;"

[Edited on 27-8-2018 by AJKOER]

boilingstone - 27-8-2018 at 13:22

Quote:

From what I've read about dichloroacetylene, I would have to strongly advise against its synthesis. According to wikipedia (again) dichloroacetylene is extremely toxic, pyrophoric, and may detonate at its boiling point. It seems there is a good reason it was mentioned in "The War Gasses...". While dibromoacetylene suffers from similar issues, apparently these issues are less severe. again, reference "The War Gasses..." I posted last time for more info

Quote:

I strongly advise against the synthesis of dichloroacetylene. We had an incident a few months ago in my university lab when a graduate student was a bit sloppy with a reaction, and dichloroacetylene was produced as a byproduct. It immediately exploded. Luckily, nobody was hurt, since the reaction was on a small scale. Anyway, intentionally trying to produce dichloracetylene is extremely dangerous. Reacting it with ozone would be sheer insanity.

We seem to be in agreement. What then of dibromoacetylene? The acetylene halides become more stable as the halides proceed down the group.

Hunterman2244 - 27-8-2018 at 13:48

How about using oxamide? Displacement to chlorine seems plausible.

clearly_not_atara - 27-8-2018 at 14:36

I would be afraid of generating cyanogen, which itself has a tendency to explode, polymerize or both.

JJay - 27-8-2018 at 16:15

If someone makes oxalyl bromide, that would be interesting since it could be substituted in many places for oxalyl chloride, but there is much more literature on oxalyl chloride. I would want to see a step that produces oxalyl chloride from oxalyl bromide.

boilingstone - 27-8-2018 at 16:32

JJay:

A quick search on prepchem shows a procedure for the opposite:
http://www.prepchem.com/synthesis-oxalyl-bromide/