October 17, 2019, 02:14:11 PM
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Topic: Hydrazines, which are toxic?  (Read 7702 times)

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Offline Enthalpy

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Re: Hydrazines, which are toxic?
« Reply #15 on: June 25, 2018, 07:31:04 AM »
Thanks wildfyr!

Err, yes, H are implied - but I had to write them in CH2O to distinguish from carbon monoxide.

Offline Enthalpy

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Re: Hydrazines, which are toxic?
« Reply #16 on: December 23, 2018, 08:47:21 AM »
TheUnassuming hinted (thanks!) at efficient N-N coupling by O2+catalyst or by electrolysis
http://www.chemicalforums.com/index.php?topic=97919.msg345959#msg345959
https://pubs.acs.org/doi/10.1021/jacs.8b05245 and https://pubs.acs.org/doi/10.1021/ja5013323
which achieves molecules as crowded as tetraphenylhydrazine, so cyclopropylmethylhydrazines look accessible. This needs a good path to dicyclopropylamine, as some previous compounds here do.

The dicyclopropyldimethyl would be slightly flammable but a mix with heavier compounds shall improve it and lower the freezing point, the isomers being welcome too.

The Osiris applet estimates that these hydrazines are harmless (but it considers Udmh as slightly carcinogenic).

The seemingly cheap N-N coupling would apply to other compounds here like diazetidyl.

Cyclopropyls are expected to weaken the N-N bond further. Bad for the heat stability, but it may improve the hypergolic ignition with N2O4.

Marc Schaefer, aka Enthalpy

Offline Enthalpy

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Re: Hydrazines, which are toxic?
« Reply #17 on: September 15, 2019, 07:40:59 AM »
Careful hand estimations of the heats of formation, as liquids at 298K, give all cyclopropylmethylhydrazines +7s specific impulse advantage over RG-1 "kerosene" rocket propellant.

The Osiris applet can't give certainty about the health risks of cyclopropylmethylhydrazines, which are 3s short of dangerous Mmh and Udmh but only 2s better than the supposedly safe diazetidylcyclopropane, so alternatives exist.

Marc Schaefer, aka Enthalpy

Offline Enthalpy

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Re: Hydrazines, which are toxic?
« Reply #18 on: September 15, 2019, 05:53:40 PM »
I tried to estimate the heats of formation of cyclopropylated and cyclobutylated diazetidines, but insufficient data lets cumulate many uncertainties.
  • Dicyclobutyl was measured by Katorgyn, so 1,2-dicyclobutylcyclobutane is accessible.
  • To 1,2-dicyclopropylcyclobutane, I applied the same +46.2kJ/mol as from methylcyclobutane to methylcyclopropane.
  • From tertiary C-C to N-N, I applied +251.4kJ/mol because it's +175.1 from propane to Mmh, +200.0 from butane, +203.1 from isobutane.
  • And I supposed that the ring strain acts on diazetidine as on cyclobutane.
N,N'-Dicyclopropyl-1,2-diazetidine is then 10s better than RG-1, as efficient as Mmh. The Osiris applet doesn't consider it badly toxic, but that's only software. C+N=10 makes it flammable if lukewarm, similarly to turpentine.

Mixing some cyclobutylcyclopropyldiazetidine raises the flash point and depresses the melting point. Being 8s better than RG-1, it wastes little performance.

While matching the perfomance of Mmh would be an achievement, dicyclopropyldiazetidine can't replace it on existing rockets, as the mix ratios differ too much. The photocoupling synthesis I suggested on June 23, 2018 is hypothetic too.

Marc Schaefer, aka Enthalpy

Offline hollytara

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Re: Hydrazines, which are toxic?
« Reply #19 on: September 15, 2019, 09:43:57 PM »
So the diazetidines:  typical C-C bond strength is 350 kJ/mol. typical N-N bond strength is much less - 165 kJ/mol.  Meanwhile, cyclobutane ring has strain energy of 110 kJ/mol - so the bond strength in the diazetidines will only be about 55 kJ/mol - that is 13 kcal/mol.  Bonds this weak can't be isolated at room temperature. 

I would be vaery careful with all of these compounds - put me in mind of mustard gases. 



Offline rolnor

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Re: Hydrazines, which are toxic?
« Reply #20 on: September 16, 2019, 05:54:54 AM »
I dont think they are alkylating but hydrazines are never non-toxic. They could be impossible to synthesize and non-stable.

Offline Enthalpy

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Re: Hydrazines, which are toxic?
« Reply #21 on: September 16, 2019, 01:50:40 PM »
Hi Rolnor, thanks for your interest!

One nice improvement here is that the hydrazines are far less volatile than Mmh or Udmh. If a leak occurs at a satellite or rocket, people won't lick it, but Mmh is as volatile as ethanol, ouch.

At least N, N'-dimethyl-1,2-diazetidine was synthesized, although in small amount using a path unsuitable to rocket amounts: ethylene bromide and sym-dimethylhydrazine, big dilution, low yield. It was stable enough to measure the 70°C boiling point. Appended is a screenshot of page numbered 28 in the report, is 39/123 in the Pdf
https://apps.dtic.mil/dtic/tr/fulltext/u2/093924.pdf

The page 80 of the document uses an estimated heat of formation for dimethyldiazetidine. I get far better figures for the estimated dicyclopropyl.

Offline Enthalpy

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Re: Hydrazines, which are toxic?
« Reply #22 on: September 16, 2019, 02:00:36 PM »
Hi hollytara, nice to read you!

To my understanding, the strain energy spreads on four bonds (N-N may reacts differently to it, but I have no data), so with your figures, N-N would retain 137kJ. Accordingly, 1,2-diazetidines were already synthesized, see page numbered 28 in
https://apps.dtic.mil/dtic/tr/fulltext/u2/093924.pdf

The authors of the report didn't investigate this compound more. They boiled the dimethyl at 1atm and 70°C without detonation, but for instance sensitivity to shocks would be no-no.

Offline hollytara

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Re: Hydrazines, which are toxic?
« Reply #23 on: September 17, 2019, 01:14:08 PM »
If they made it, they made it. I read about the cyclic hydrazine with one of the N's in a 4 membered ring - it was pretty reactive, and ring opened quite easily.   

Offline rolnor

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Re: Hydrazines, which are toxic?
« Reply #24 on: September 17, 2019, 09:56:30 PM »
OK, the 3-membered is reactive I know, its maybe different when the nitrogen in the 4-membered ring is connected to another nitrogen atom. The mustard gas type of compounds are different with the ability to cross-link DNA etc.

Offline hollytara

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Re: Hydrazines, which are toxic?
« Reply #25 on: September 19, 2019, 12:42:45 PM »
There is this issue of "neighboring group participation" which is what makes the mustards so reactive. 

Offline Enthalpy

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Re: Hydrazines, which are toxic?
« Reply #26 on: September 30, 2019, 07:50:38 PM »
Synthesis of 1,2-diazetidines: a thesis exists
http://wrap.warwick.ac.uk/38106/7/WRAP_THESIS_Brown_2011b.pdf
especially page 18 of the pdf, marked page 8, gets 60% yield with
RNNR+BrCCBr -> R-diazetidine-R
where R is isopropyl, giving me hope for cyclopropyl.
Whether ethylene oxide is better?
I've seen no mention of photoaddition there.

Just below,
"These  diazetidines  were  found  to  be  very  stable  compounds."
but this is on a chemists' scale. Rockets are more demanding.

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