Exobiology Using Hydrazine as an Alternative (or Supplementary) Solvent to Water

Question

My question is this - are there any reasons why hydrazine may jump out as a poor solvent for a complex system such as life?

I am working on a worldbuilding sci-fi project and I was looking through a number of molecules that potentially could replace or supplement water on another planet.

The general background is that I'm trying to sketch up some interesting exotic planets for a sort of encyclopedia of known worlds. For one of the less earthlike worlds, I was thinking of using hydrazine (N₂H₄) as the dominant thalassogen (or, a substance capable of forming a planetary ocean).

In the context of the universe, this type of a planet is exceedingly rare, as water is the most common thalassogen on terrestrial worlds (save for maybe planets which are exceedingly close to their stars and have various molten materials).

It's stats seem pretty reasonable for thalassogen including:

• Hydrazine's liquid range of 112°C/202°F (2°C-114°C/35°F-237°F)
• Hydrazine hydrate's liquid range is even broader (-52°C-120°C/-61.6°F-248°F)
• A comparible density to that of water, being slightly more dense at 1.021 g/cm³, and hydrazine hydrate having a slightly higher density still at 1.032 g/cm³.
• Hydrazine hydrate seems to be extremely beneficial for keeping a wide liquid range which may allow for life to evolve into colder or potentially hotter environments.
• Hydrazine is comprised of, N₂H₄ - both constituents, Nitrogen and Hydrogen are exceedingly common with Hydrogen being the most common of all elements and Nitrogen being fairly "easy" for stellar nucleosynthesis to generate.
• Hydrazine is also polar and thus allows for hydrogen bonding.

Is there anything here that's a deal breaker in your opinion? I'd love to get some more thought on it.

Thank you in advance.

Answer 1

Hydrazine is a powerful reducing agent and would present problems for organic chemicals for example its ability to convert carbonyl groups to methylene groups. Give the widespread occurrence of carbonyl groups in nature this would present difficulties for a viable biochemistry.

https://en.wikipedia.org/wiki/Wolff%E2%80%93Kishner_reduction

It is also catalytically broken down by a range of metals and metal oxides slowly or quickly and does not spontaneously form so would eventually disappear and not reform unless great care was taken to exclude any materials that might catalyse its decomposition.

Answer 2

The main problem I see is that, while water is easily created by the reaction of oxygen and hydrogen, having natural production of large amounts of hydrazine seems very difficult.

And to have oceans of hydrazine you would need quite some of it.

Moreover, since it reacts and decompose with some substances, you would also need to carefully tune the composition of your rocks to avoid anything that would cause hydrazine to decompose.

Answer 3

Hydrazine is an extremely high energy molecule. It does not easily form spontaneously, and it decomposes easily and violently--enough so that it is used as a monopropellant rocket fuel. Low-temperature life that exists near the freezing point of hydrazine hydrate might be artificially engineered, but it's completely implausible that a planet would naturally form with an entire ocean of the stuff, and even at -50C, such engineered lifeforms would have to worry about spontaneously exploding.