Hi sriram, thanks for your interest!
Most amines are hypergolic with tetroxide, tertiary amines better so, hydrazines even better. A rocket engine a very fast
ignition by contact, and this is uncommon.
One reason is that accumulation of propellants in the chamber before ignition is a show stopper. An other reason is that hypergolic propellants don't demand a perfectly stable flame at the beginning of the chamber, since they can catch fire downstream occasionally if needed, and this eases the design of the chamber, and can make it smaller.
Additional choice criteria are (1) safety (2) safety and (3) safety. TMEDA with C+N=8 is as volatile and flammable as gasoline, nothing desired. PMDETA is good for this with C+N=11.https://www.chemicalforums.com/index.php?topic=79637
Diamines mass-produced for polyamines are a good start too. Permethylating improves the liquid range, important.
Though, my goal is not hypergolicity, because nobody wants to keep the toxic and inefficient tetroxide. The future is liquid oxygen. I have interest in amines because they bring 2-3s better performance than the alkane homologues and are easier to produce. Among these, PMDETA is my standard choice for safety, easy production, liquid range, and some performance improvement over RG-1 "kerosene" (it's nearer to Diesel oil). More exotic compounds, including the hydrazines of doubtful
harmlessness, are a speculative attempt at higher performance, exceeding the strained but probably sound amines like diazetidylcyclopropanehttps://www.chemicalforums.com/index.php?topic=86972.0
From my ramblings, you can trust my estimates for the heat of formation and the performance. The boiling and flash points are reasonable. The melting points are always doubtful. The toxicity of the hydrazines is essentially unknown, most are strongly undesired, but the present thread exists because aminoguanidine was tested as a drug and the volunteers survived. And from the synthesis paths I propose, don't believe a word, I'm not a chemist.
Whether engines and stages will exist with such propellants? They gain 4-7s while methane gains 11s. I'd prefer a safer strained amine, storable and denser than methane, but SpaceX and Blue Origin have already adopted methane.https://www.chemicalforums.com/index.php?topic=79637.msg337420#msg337420
The other option is to cool the engine with the liquid oxygen rather than the fuel: this enables better fuels and more pumping cycles where ethylene is a trivial choice, but other fuels can be more interesting.