Nitryl cyanide: synthesis, properties and potential applications in EM science

In a recent article published in the Angewandte Chemie journal a team of scientist from the Loker Hydrocarbon Research Institute and Department of Chemistry synthesized a small but very important molecule called nitryl cyanide [1]. It’s structure is shown below:

Synthesis:

Nitryl cyanide was synthesized by reacting nitronium tetrafluoroborate (NO₂BF₄) with tert-Butyldimethylsilyl cyanide (tBuMe₂SiCN) in nitromethane (CH₃NO₂) as a solvent at -30°C:

Fractional condensation was used for the purification of nitryl cyanide. A yield of 40% of nitryl cyanide (with >95% purity) was obtained after three fractional condensation.

Properties:

Nitryl cyanide is a colorless liquid at room temperature. It’s melting point is -85+/-1°C. The density of the liquid at -79°C is 1.24+/- 0.08 g/cm³. Nitryl cyanide is stable at room temperature, quotes from [1]:

“The thermal decomposition of NCNO₂ was studied by heating the compound in a stainless steel cylinder, separating the products by fractional condensation, and analyzing them by IR spectroscopy. Heating for one hour to 50 and 100°C, respectively, resulted only in little decomposition with most of the NCNO₂ being recovered unchanged, and heating to 140°C for several hours was required to achieve complete decomposition. The major decomposition products were CO₂ (80 mol% based on carbon) and N₂, but smaller amounts of NO and some NO₂ and N₂O were also observed...”

Importance as an energetic material:

The heat of formation of nitryl cyanide in the liquid state was estimated to be +43.9+/-2 kcal/mol which is pretty high for a small molecule. The molecule of nitryl cyanide has a zero oxygen balance: one mole of nitryl cyanide yield one mole of nitrogen (N₂) and one mole of carbon dioxide (CO₂). Nitryl cyanide behave as an excellent propellant, quotes from [1]:

“As NCNO₂ has an excellent oxygen balance and a large positive heat of formation, it might be of interest as a high energy density material (HEDM). We have estimated the specific impulse (Isp, rocket propellant performance) of NCNO₂ in vacuum, and predicted a value of 343 s. This value can be compared to 240 s for hydrazine. It even exceeds that of a standard (NO₂)₂/hydrazine bipropellant by 10 s.”

The authors didn’t mention any detonation performance for nitryl cyanide. Based on the reported density and heat of formation, I calculate the detonation performance (detonation velocity and pressure) using the BKW thermochemical code [2]:

D_CJ= 6.62 km/s

P_CJ= 158 kbar.

These generally low detonation performance are directly linked to the low condensed density (1.24 g/cm³ of nitryl cyanide.

Nitryl cyanide as an important building block for other energetic materials:

Theoretical calculations have shown that many molecule displays excellent performance as explosive and propellant. Two of these molecules are shown below:

The properties of 2,4,6-trinitro-1,3,5-triazine are taken from [3] while the performance of the cubane derivative was taken from [4]. These two theoretical molecules are very interesting as explosive and propellant. Nitryl cyanide has been proposed as a building block for the formation of the two molecules shown above [5]:

The calculations shows that the reaction is exothermic (ΔE(0°K)= -70.2 kcal/mol) for reaction (2) which is due to aromatic stabilization of 2,4,6-trinitro-1,3,5-triazine.

Conclusion:

Nitryl cyanide has been synthesized with moderate yield (40%) from nitronium tetrafluoroborate (NO₂BF₄) and tert-Butyldimethylsilyl cyanide (tBuMe₂SiCN) in nitromethane (CH₃NO₂) as a solvent at -30°C. Nitryl cyanide is a liquid with a density of 1.24 g/cm³ and is stable at room temperature. The calculated energetic performance shows that nitryl cyanide possess excellent propellant performance (Isp= 343 s) and moderate to low detonation performance (calculated via BKW thermochemical code). Nitryl cyanide is also a potential building block for the synthesis of other interesting energetic molecules, namely 2,4,6-trinitro-1,3,5-triazine and 1,3,5,7-tetranitro-2,4,6,8-tetraazacubane.

References:

[1] M. Rahm, G. Bélanger-Chabot, R. Haiges, K. O. Christe, Angew. Chem. Int. Ed. 2014, 53, 6893-6897.

[2]Mader, C. L. 1963. Detonation properties of condensed explosives computed using the Becker-Kistiakowsky- Wilson equation of state. Report LA-2900. Los Alamos Scientific Laboratory

[3] YAKUP ÇAMUR, A COMPUTATIONAL STUDY ON NITROTRIAZINE DERIVATIVES, MIDDLE EAST TECHNICAL UNIVERSITY, 2008, Master thesis.

[4] Peter POLITZER, Pat LANE and Jane S. MURRAY, CEJEM, 2011, 8(1), 39-52.

[5] Peter POLITZER, Pat LANE and John J.M. Wiener, cyclooligomerizations as possible routes to cubane-like systems, OFFICE OF NAVAL RESEARCH, contract N00014-99-1-0393, 1999.

Dany.

[Edited on 15-12-2014 by Dany]

Thanks Dany,
Very nice finding and infos
I will comment deeper later on this compound and related multimers.

For now on, I'm just curious about the detonation parameters you calculated...if you go just 7 degrees Celcius lower in temperature, you would be below the melting point of the molecule; the density would then be higher and close to 1,348 g/ccm (if it display aliphatic properties) or to 1,400 (if it display aromatic properties - due to the triple bond -C#N and conjugated -N(=O) of the nitro group).

--> Could you redo the calculations of Dcj and Pcj with that info? Thanks in advance .

BTW, I wonder what is precisely the impact of the freezing/lowering of the temperature on the detonation parameters, since density is temperature dependant; dillatation coefficients might be considered reversely as a contraction coefficient and expands or constricts the material linearly over wide temperature areas (dillatation/contraction coefficients are larger for organic materials than for mineral or metalic materials...what is good news for this specific energetic material application)...
--> Theorycaly absolute zero would result in maximum density but the explosive material migh become unsensitive, or at a certain stage lose power due to the heat capacity of the material that has to be integrated from zero to ambiant temperature into thermodynamic calculations...
--> Each explosive might display an optimum minimal temperature to maximise density and output energy without loosing initiability!


Hereunder the results from Engager's Sciencemadness detonation utility program for the 3 densities...


[Edited on 17-12-2014 by PHILOU Zrealone]

The first theoretical study (via ab initio method) performed on nitryl cyanide and it's isomers was performed by Anatoli KORKIN and Rodney BARTLETT back in 1996 [1]. They predicted that nitryl cyanide and two of it's isomers should be stable and observable experimentally. The two other isomers are shown below:

The stability decrease as one goes from nitryl cyanide to isomer (II).
Nitryl cyanide> (I) > (II). However (I) and (II) should be observable.

deltaH if the authors didn't get any polymerization product from heating this doesn't mean that the idea of using nitryl cyanide as precursor for the formation of the triazine and azacubane is wrong. Nobody said that only by simple heating you will get the desired polymerization products. Maybe the formation should be carried out using a catalyst or via light irradiation using photochemistry.

Bert, nothing is said about the toxicity of nitryl cyanide. However this compound is reactive. Nityl cyanide is incompatible with fluorides, Lewis acids [BF₃ and B(C₆F5)₃], elemental mercury, amines, and K₃PO₄.

For a given propellant, the exact mechanism of decomposition and the nature of decomposition products as well as their quantity in a rocket motor is the one million dollar question. This is so difficult to predict due to the high combustion temperature encountered in a rocket motor which influence the chemical equilibrium for the different reaction that may occur in this environment.

Philou, the D_cj and P_cj of nitryl cyanide at 1.348 g/cm³ and 1.4 g/cm³ are:

For 1.348 g/cm³: D= 6.96 km/s; P= 187 kbar.

and

1.400 g/cm³: D= 7.13 km/s; P= 201 kbar.

Thanks for your own detonation calculation but these calculations should be checked for errors. I see that you have used 43.9 kJ/mol for your calculation while the true unit is kcal/mol...a big difference.

Also, the detonation temperature are constant in all your calculations at the three density which is impossible.

References:

[1] A. A. Korkin, J. Leszczynski, R. J. Bartlett, The Journal of Physical Chemistry 1996, 100, 19840-19846.

Dany.

[Edited on 18-12-2014 by Dany]

This molecule looks highly reactive (speculative, I know, but some reasoning why below), so I doubt you would need a catalyst to decompose it. Your main problem would be preventing detonation or progression of a deflagration from the exhaust into the fuel tank.

I might be wrong, but perhaps it would behave similar to the insanely toxic cyanogen halides or cyanogen itself. The nitro group is strongly electron withdrawing and I would hazard a guess that the C-NO2 bond in that molecule is weak and easily dissociated.

Since it's so new... I'd treat it as extremely toxic and able to detonate, until proven otherwise.

The author who synthesized nitryl cyanide didn't mention how they calculate the specific impulse I_sp which is 343 s for this compound.

we present here a simple (but rough) formula for the rapid estimation of I_sp. This formula can be applied to monopropellant as well as to bipropellent (e.g., H₂-O₂ system).



The unit of I_sp is the second. If one mole of nitryl cyanide decompose into one mole of CO₂ and one mole of N₂, the heat liberated is Q= -138 kcal/mol. The molecular weight of the gases is 72 g/mol. Using the above formula, one get an I_sp= 367 s, which is relatively close to the value of 343 s given in the paper. (the absolute value of Q is used).

For more information on this formula see the following report:

Rosen, G. Final Report for Project Propulsion Applications of Free Radicals and Electronically Excited Metastable Species

Dany.


[Edited on 19-12-2014 by Dany]

Since I had fun with 'burning' dimethylcyanamide with the open simulation software COCO, I figured I could give this a stab too.

STEP ONE: Adiabatic flame temperature calculation

This one was considerably more challenging than combusting dimethylcyanamide. My original idea was to approximate nitryl cyanide as one mole each of carbon, nitrogen and oxygen and feed that into the Gibbs reactor model to get a composition and adiabatic flame temperature. I would have simply added the heat of formation of nitryl cyanide as an energy feed stream into the reactor to account for the difference in enthalpies.

However, carbon is not a listed component in the databank, so I had to be a little shifty

What I did is to feed one mole of benzene as my carbon source, then split off the water after combustion, cool it to STP and add this heat back into the Gibbs reactor. I then also subtracted the heat of formation of benzene and water from the heat of formation of nitryl cyanide entering as the energy stream.

I have a funny feeling I've got a sign error in there somewhere

So by going this roundabout route, I've done the thermodynamic equivalent (hopefully) of feeding in carbon. Thermodynamics is not path dependent... so one just needs to draw a big black box over the whole thing and make sure that the IN's and OUT's are correct and accounted for.

Anyhow, the simulation is attached below, if you haven't installed COCO by now... do it... it's damn powerful and versatile!

The adiabatic flame temperature, tentatively, is a whopping ~4100°C

Not really surprising considering that this is a non-water producing EM, but still, it's f@$ing high.

Interestingly, it's so high, that a significant amount of CO2 is dissociated to CO and O2, in other words, while it has an OB of 0, the REAL/effective OB is quiet +ve and so the monopropellant would benefit from mixing with another. This could go some way to stabilising it by dilution and also lower effective costs (once an alternative synthesis is found)?

There's also lots of nitric oxide in the there as well.

The decomposition products per mole of nitry cyanide decomposed by equilibrating at 4100°C are:

0.265 mol. O2
0.936 mol. N2
0.342 mol. CO2
0.658 mol. CO
0.128 mol. NO

Please someone check this for me, attached simulation below. Once we're all satisfied with this, I can proceed with the ISP calculation by working out an nozzel exhaust velocity and finally the ISP.

EDIT: Corrected too much oxygen in feed error, originally was feeding 9 moles O2 per mole of benzene, should have been 7.5 moles O2, which it is now.

Attachment: nitryl cyanide combustion.fsd (249kB)
This file has been downloaded 728 times

References:

Download COCO from http://www.cocosimulator.org/

[Edited on 19-12-2014 by deltaH]

Quote: Originally posted by Dany

deltaH if the authors didn't get any polymerization product from heating this doesn't mean that the idea of using nitryl cyanide as precursor for the formation of the triazine and azacubane is wrong. Nobody said that only by simple heating you will get the desired polymerization products. Maybe the formation should be carried out using a catalyst or via light irradiation using photochemistry. Philou, the Dcj and Pcj of nitryl cyanide at 1.348 g/cm<sup>3</sup> and 1.4 g/cm<sup>3</sup> are: For 1.348 g/cm<sup>3</sup>: D= 6.96 km/s; P= 187 kbar. and 1.400 g/cm<sup>3</sup>: D= 7.13 km/s; P= 201 kbar. Thanks for your own detonation calculation but these calculations should be checked for errors. I see that you have used 43.9 kJ/mol for your calculation while the true unit is kcal/mol...a big difference. Also, the detonation temperature are constant in all your calculations at the three density which is impossible.

Philou and deltaH thanks for the calculations. Philou, The calculated detonation pressure (350 kbar) is too fantastic for a density of 1.4 g/cm³. I will stick to my reliable thermochemical code calculations. You can try to repeat the calculation of D_CJ and P_CJ (we are not interested in Q or T_CJ right now) with the simple method of Kamlet and Jacobs [1] which is known to be very reliable. deltaH, proceed to the I_sp calculation based on your method to see if you will obtain a value close to 343 s.

In connection with nitryl cyanide, it seems that trinitromethyl cyanide exist, and had existed long time ago.



The only english language paper which mention trinitromethyl cyanide is the article of WILSON et al. [2] published in 1947. Quote from [2]:

"Trinitromethane (nitroform) was first prepared by Schischkoff (Annalen, 1857, 101, 216) by the action of water or alcohol on trinitromethyl cyanide, and later several methods for its preparation from tetranitromethane were described..."

I've searched the old Annalen journal (which is now the European journal of organic chemistry, EurJOC) and found I found the 157 years old paper which is written in German. I've attached the paper below so if one of the members (Philou?) knows German he can help us to understand what the paper said about trinitromethyl cyanide (reactivity, synthesis, etc...).

References:

[1] M. J. Kamlet and S. J. Jacobs, “Chemistry of Detonation. I. A Simple Method for Calculating Detonation Properties of C, H, N, O Explosives,”
J. Chem. Phys. 48 (1), 23–35 (1968).

[2] W. S. Reich, G. G. Rose, W. Wilson, Journal of the Chemical Society (Resumed) 1947, 1234-1237.

Dany.

Attachment: German paper on trinitromethyl cyanide.pdf (230kB)
This file has been downloaded 542 times


[Edited on 20-12-2014 by Dany]

Quote: Originally posted by PHILOU Zrealone

Tris-trinitromethyl-triazine : An article of this was provided by Nicodem somewhere into the forum.