Sciencemadness Discussion Board

Why did my ETN turn blue, then green?

Chisholm - 21-6-2017 at 06:49

I'm aware that molecules with nitro groups can form colored complexes with amines; What surprised me was that I got two different colors out of the same two substances, and I don't fully understand why.

So I've synthesized ETN twice; once via the addition of erythritol to SA+AN according to instructions I found here, which gave dismal yields, and again (much more successfully) with addition of erythritol to yellow fuming nitric acid followed by precipitation with sulfuric acid.

Long story short, in each case I dissolved the ETN in dichloromethane, added a few milligram-sized flakes of freebase diphenylamine (which is also soluble in DCM) and waited for the DCM to evaporate before melt-casting the product.

In the first case, the melt-cast product was a deep navy blue bordering on indigo; in the second, it was a deep forest green. (These colors were apparent prior to melt-casting as tinges to the crystals concentrated at the tip, where evaporation had been fastest.)

Even weirder, when I let 50mL of a saturated DCM solution of ETN with a few mg diphenylamine evaporate, there were blue spots above the level of the liquid where traces of ETN+DPA had dried, but the main deposit (~12 g ETN) was green.

So what made the absorption bands shift by over 60 nm? Did some DPA convert to diphenylnitrosoamine? Or are there multiple ETN+DPA complexes with different mole ratios?

PHILOU Zrealone - 21-6-2017 at 08:35

Ohhh J...

Noone can use keywords and a simple search engine anymore? Maybe should there be a specific course to learn how to use a search engine...

"Nitrosation diphenylamine" afwords into Google...the following document...
Took me 5 seconds...to find it and 5 seconds to open it to check...result of the test blue and green color...


Test diphenylamine for nitrocompounds

Bert - 21-6-2017 at 08:44

Diphenylamine can form up to 12 different compounds as it takes on up to 6 NOX. You probably have several different products (and proportions of these) from that process.

Google will tell you more than I have time to.

Chisholm - 23-6-2017 at 06:36

Quote: Originally posted by PHILOU Zrealone  
Ohhh J...

Noone can use keywords and a simple search engine anymore? Maybe should there be a specific course to learn how to use a search engine...

"Nitrosation diphenylamine" afwords into Google...the following document...
Took me 5 seconds...to find it and 5 seconds to open it to check...result of the test blue and green color...


Test diphenylamine for nitrocompounds


No need to get snippy; I found that, but it specifically dealt with aliphatic nitro compounds, not nitric esters.

[Edited on 6-23-2017 by Chisholm]

Also, there is no mention of a green color; that paper only discusses the blue color.

Also also, SHIT. Does the blue color mean that there is still trace sulfuric acid dissolved in the ETN??!!

[Edited on 6-23-2017 by Chisholm]

PHILOU Zrealone - 23-6-2017 at 12:20

Not only nitrocarbons R-NO2, but nitrosamines R-N(-NO)-R', nitrates and nitrites...and oxydising agents...do provide the blue color.

Exctracted from the provided document:
"Spectroscopic measurements indicate that the blue color in the diphenylamine test with nitrosating agents is similar to that produced by oxidizing agents. It is probably caused by colored phenazine and benzidine derivatives. A possible free radical mechanism for the reactions involved is presented."

"The blue color that has been obtained by the action of nitrosamines, nitrates, nitrites, and aliphatic nitrocompounds on diphenylamine in sulfuric acid has been regarded as a specific test for these substances in the absence of various oxidizing agents that also produce a blue color."

So yes you eather have traces of H2SO4, HNO3 or HNO2 into your product...thus all proof of a decomposition reaction taking place...the test is very sensitive thus maybe only trace decomposition is occuring but stil bad news for storage and safety.

Hydrolysis of R-ONO2 produces R-CH2-OH and HO-NO2.

Homolytic decomposition provides R-CH2O° and NO2° then R-CH=O + HONO + heat

2 HONO --> H2O + N2O3

Blue with yellow = green ...so probably that during decomposition of your ETN...you have at the same time a yellowing...this is often the case with nitric esters...yellowing is bad news...

[Edited on 23-6-2017 by PHILOU Zrealone]