# Is there a quantitative test/analysis technique that can determine if some chloroform has degraded into phosgene?

Before I go to use any chemical that I've had in storage for a while, I try to check if it's degraded into something else (e.g.: checking the $$\ce{H2O}$$ content of $$\ce{H2O2}$$, checking for $$\ce{H2O2}$$ in $$\ce{Et2O}$$, etc.). This can usually be done using the appropriate test strip.

I have a 3/4 full bottle of chloroform that's been sitting on a shelf for about a year (probably less, actually), in an amber bottle to restrict the amount of light that can get to the chloroform. I'm aware that chloroform can break down into phosgene, and I know there are some ways to test for this, but I was hoping for a quick quantitative test that can be done without any hassle, but I can't seem to find anything out there. The Wikipedia page for chloroform states:

Suspected samples can be tested for phosgene using filter paper (treated with 5% diphenylamine, 5% dimethylaminobenzaldehyde in ethanol, and then dried), which turns yellow in phosgene vapor.

I don't have either of the diphenylamine or the dimethylaminobenzaldehyde, and would prefer not to have to purchase them just for this simple test (I don't have any use for either chemical currently). Does anyone know if there is a simple quantitative test that accomplishes the same thing? Preferably a test strip.

• Phosgene reacts with ethanol. Thus, if your chloroform is ethanol protected then your risk is minimal. – Mathew Mahindaratne May 19 at 8:03

Not a quantitative test but a good proof of phosgene. You could use a pH paper strip. Chloroform should show a neutral pH, but if there is phosgene/HCl the paper will show acidity.

• I see - That seems simple enough! Thank you – Justin Jun 7 at 9:18

I admire your safety precautions. Like we always check for peroxide content in older ether bottles, we should also test older chloroform bottles, specifically those of alkene-preserved, for the presence of phosgene (Ref.1). The C&E News letter recommended use of filter paper strips, wetted with 5% diphenylamine, 5% dimethylaminobenzaldehyde and then dried, which turn yellow in phosgene vapor (a qualitative test). Note that as test strips age they become light yellow/brown, they will still show a significant change to bright yellow upon detection of phosgene (Wooley Lab).

There are also Draeger tubes available for phosgene testing, but they are kind of expensive (e.g., check on Shopcross.com). The Draeger tube test uses the general reaction of an aromatic amine with phosgene to obtain the corresponding aromatic isocyanate (I believe), which has long been known. However, their aromatic amine turns red in the presence of phosgene. It has been suggested that such reactions proceed thru the acid salt of the amine such as an amine hydrochloride or an amine-$$\ce{CO2}$$ adduct either by forming the salt in situ in the process or by starting with the salt, to form the corresponding aromatic carbamyl chloride, which in turn is decomposed to the isocyanate with liberation of hydrogen chloride.

In addition, qualitative (and can develop for quantitative) analysis by GC/MS would work as well. However, Ref.1 has used UV-vis colorimetric quantitation described in Ref.2. The abstract states that:

A reagent consisting of 0.25% 4-p-nitrobenzylpyridine and 0.5% N-benzylaniline in diethylphthalate was tested and proved to be highly sensitive and relatively specific for the spectrophotometric determination of phosgene in air. Concentrations under $$\pu{0.1 ppm}$$ of phosgene in air may be determined with reliability. The color developed with the reagent was stable for several hours and only slightly affected by normal ambient humidity. None of the following substances interfered with the reaction: hydrogen chloride, chlorine, chlorine dioxide, carbon tetrachloride, chloroform, trichloroethylene, tetrachlorethylene, and dichlorodifluoromethane in concentrations likely to be encountered under industrial conditions.

It seems there is some development in teststrips containing a fluorophore for phosgene detection (See diagram below; Ref.3), which changes the color from blue to green with a hand-held UV light in the presence of phosgene.

References:

1. Eric Turk, “Phosgene from chloroform,” Chemical & Engineering News 1998, 76(9), p 6 (DOI: 10.1021/cen-v076n009.p006).
2. M. H. Noweir, E. A. Pfitzer, “An Improved Method for Determination of Phosgene in Air,” American Industrial Hygiene Association Journal 1971, 32(3), 163–169 (https://doi.org/10.1080/0002889718506431).
3. H. Xie, Y. Wu, F. Zeng, J. Chena, S. Wu, “An AIE-based fluorescent test strip for the portable detection of gaseous phosgene,” Chem. Comm. 2017, 53(70), 9813–9816 (DOI: 10.1039/c7cc05313d).