I have been synthesizing TCPO (bis(2,4,6-trichlorophenyl) oxalate) for chemiluminescent reactions, using 2,4,6-trichlorophenol and oxalyl chloride.

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Since I am tired of paying for oxalyl chloride (and hazard class 3 shipping), I wish to find a synthetic route to produce my own stock.

The most common synthesis of oxalyl chloride uses oxalic acid and phosphorus pentachloride. This would reduce the cost, but is also problematic because phosphorus chlorides are considered to be drug precursor (21 CFR 1310.02), still too expensive, and hazardous to ship.

Can anyone recommend a synthetic route to oxalyl chloride that does not use phosphorus? Or an alternate (safer / easier / less expensive) route to TCPO?

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    $\begingroup$ I believe you can try to find a route via transesterification. Excess of TCP heated with dialkyloxalate in presence of catalitic amound of strong base should give the desired product. The produced alcolohol should be distilled off to enforce the reaction. I highly discourage use of PCl5 or similar compounds outside a professional lab. $\endgroup$
    – permeakra
    Jul 26 '15 at 14:44
  • $\begingroup$ I would like to point out to you that TCP, or 2,4,6-trichlorophenol, is carcinogenic and I would not recommend using this. $\endgroup$
    – LiamH
    Jul 29 '15 at 10:13
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    $\begingroup$ @reluctantmathematician there are several notions of synthesis of acetyl chloride using $\ce{S2Cl2}$. This compound is not much better than $\ce{PCl5}$, but can be prepared from reasonably available and unregulated chlorine and sulfur (Chlorine can be obtained by reaction of hydrochloric acid and bleach, but it should be dried by bubbling through sulfuric acid). $\ce{S2Cl2}$ should work for oxalyl chloride as well. That said, I think that buying oxalyl chloride is preferable, and transesterification is even better. $\endgroup$
    – permeakra
    Aug 3 '15 at 4:20
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    $\begingroup$ T3P (n-propylphosphonic anhydride) is also another useful coupling agent for esters $\endgroup$
    – Beerhunter
    Aug 3 '15 at 16:46

Most amide coupling agents are suitable for esters. Feast your eyes on: Amide bond formation - beyond the myth of coupling reagents.

This lists old favourites such as CDI, carbodiimides, etc. A lot of it is overkill. The water soluble carbodiimides might be preferred for ease of urea removal later.

The likes of CDI or $\ce{Ac2O/DMAP}$ can react with your phenol when over-stoichiometric amounts are used.

Alternatives could be: boronic acid derivatives e.g. phenylboronic acid catalysis; scandium or yttrium triflate catalysts (all requiring water removal, but a Dean-Stark could be used if a water immiscible solvent is used); dimethyl oxalate (already suggested) but in conjunction with Takasago's ZnTAC24 catalyst. MeOH removal by distillation is required, which is quite trivial for such a volatile component.


i think you should use oxalic acid and convert it to oxalyl chloride by thionyl chloride.take a few mL of thionyl chloride and put oxalic acid into it and reflux for about three to four Hr, evaporate the remaining thionyl chloride. i used this method for the preparation of benzoyl chloride


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