Hydrazine
Properties
| State | Liquid (colorless, fuming, with ammonia-like odor) |
| Color | Colorless |
| Solubility | Miscible with water; soluble in ethanol and methanol |
| Melting Point | 2°C |
| Boiling Point | 114°C |
About Hydrazine
Hydrazine (N2H4, 32.045 g/mol) is the simplest stable N-N single-bonded compound and one of those reagents that sits at the intersection of beautiful synthetic utility and genuine danger. Structurally it's two amine groups stitched together — H2N-NH2 — and the N-N bond's modest dissociation energy (~270 kJ/mol) plus high heat of formation (+50.6 kJ/mol) is the source of both its rocket-propellant chemistry and its reducing power. In organic synthesis, hydrazine is the workhorse for the Wolff-Kishner reduction: ketone or aldehyde plus N2H4 in hot KOH/diethylene glycol forms the hydrazone, which then loses N2 to give the methylene group. It's the standard answer for reducing a carbonyl all the way to CH2 when your substrate can't survive Clemmensen acidic conditions. It's also the precursor for synthesizing pyrazoles, indazoles, and triazines, and it makes hydrazones that are used to deprotect cyclopentadiene-derived auxiliaries. In aerospace, anhydrous hydrazine and its methylated relatives (MMH, UDMH) power spacecraft thrusters because they're hypergolic with N2O4 — they ignite on contact with no spark needed, which is exactly what you want when you're trying to restart an attitude-control thruster in deep space. The Apollo lunar module's descent and ascent engines both ran on Aerozine 50 (50/50 hydrazine/UDMH). In power plants, hydrazine is dosed into boiler feedwater at low ppm to scavenge dissolved O2 and prevent corrosion: N2H4 + O2 → N2 + 2 H2O.
Where you'll encounter it
If you've ever read about a satellite's station-keeping burns, run a Wolff-Kishner reduction in a sophomore organic lab, or worked in a power plant where boiler chemistry mattered, you've intersected with hydrazine — though the lab version is almost always the much safer hydrazine hydrate (N2H4·H2O) rather than the anhydrous form. The 35% aqueous bottle on the shelf is roughly 7 M hydrazine in water; weigh out 5 mL and you have enough for a gram-scale Huang-Minlon protocol in diethylene glycol at 200 °C, where the hydrazone forms first and then loses N2 over a few hours of reflux. In the boiler-treatment world, the dosing pump runs at 50–200 ppb to scavenge dissolved O2 below the threshold where ferrous metals start pitting. Spacecraft engineers, meanwhile, treat anhydrous N2H4 like the hypergolic propellant it is — separate fill lines, no shared seals, full SCAPE suits during loading.
Common Uses
- Wolff-Kishner reduction of ketones and aldehydes to methylene groups
- Hypergolic propellant in spacecraft attitude-control thrusters (with N2O4 oxidizer)
- Oxygen scavenger in high-pressure boiler feedwater (dosed at 50-200 ppb)
- Reducing agent for nickel and cobalt salts in electroless plating baths
- Synthesis precursor for pyrazoles, triazines, and azo dyes
- Foaming agent precursor (azodicarbonamide) for expanded plastics
- Reducing agent in semiconductor cleaning and metal-ion removal
Safety Information
Highly toxic and a confirmed animal carcinogen — IARC Group 2A (probable human carcinogen). OSHA PEL is 1 ppm (8-hr TWA, skin notation); ACGIH TLV is 0.01 ppm with skin notation. Penetrates intact skin readily. Symptoms of acute exposure: severe irritation, central nervous system depression, hemolytic anemia, liver damage, seizures. Chronic exposure linked to lung, liver, and nasal tumors. Ignition temperature is only 24-270 °C depending on surface (some metals catalyze decomposition at room temperature). GHS: H226 (flammable liquid), H301+H311+H331 (toxic by all routes), H314 (severe burns), H317 (skin sensitizer), H350 (carcinogen Cat 1B), H410 (very toxic to aquatic life). Handle only in a fume hood with full PPE — splash apron, face shield, neoprene gloves. Most academic labs now use hydrazine hydrate (much less hazardous than anhydrous) and only at gram scale.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.