Monomethylhydrazine (MMH) is a volatile hydrazine chemical with the chemical formula CH3(NH)NH2. It is used as a rocket propellant in bipropellant rocket engines because it is hypergolic with various oxidizers such as nitrogen tetroxide (N2O4) and nitric acid (HNO3). As a propellant, it is described in specification MIL-PRF-27404.
MMH is a hydrazine derivative that was once used in the orbital maneuvering system (OMS) and reaction control system (RCS) engines of NASA's Space Shuttle, which used MMH and MON-3 (a mixture of nitrogen tetroxide with approximately 3% nitric oxide). This chemical is toxic and carcinogenic in small amounts, but it is easily stored in orbit providing moderate performance for very low fuel tank system weight. Recently the European Space Agency (ESA) has attempted to seek new options in terms of bipropellant rocket combinations to avoid poisonous chemicals such as this and its relatives.
MMH and its chemical relative unsymmetrical dimethylhydrazine (UDMH) have a key advantage that they are stable enough to be used in regeneratively cooled rocket engines. The Apollo Lunar Modules used a one-to-one mixture of hydrazine and UDMH (called Aerozine 50, or A-50) as one part of the rocket fuel for lunar landings and takeoff: the rocket motors formed a hypergolic mixture of the hydrazines with liquid dinitrogen tetroxide as the usual oxidizer. (Otherwise, red fuming nitric acid works.) About three tons of mixed hydrazines and four and one half tons of the oxidizer were required for each landing, and about one-third of those amounts for the lunar take-off to orbit.
Monomethylhydrazine is believed to be the main cause of the toxicity of mushrooms of genus Gyromitra, especially the false morel (Gyromitra esculenta). In these cases, MMH is formed by the hydrolysis of gyromitrin.
A known use of MMH is in the synthesis of Suritozole.
3D model (JSmol)
|Molar mass||46.07 g·mol−1|
|Appearance||Fuming, colourless liquid|
|Density||875 mg mL−1 (at 20 °C)|
|Melting point||−52 °C (−62 °F; 221 K)|
|Boiling point||87.50 °C; 189.50 °F; 360.65 K|
|Vapor pressure||5.00 kPa (at 20 °C)|
Refractive index (nD)
|134.93 J K−1 mol−1|
|165.94 J K−1 mol−1|
Std enthalpy of
|54.14 kJ mol−1|
Std enthalpy of
|−1305.8–−1304.6 kJ mol−1|
|Safety data sheet||inchem.org|
|GHS signal word||DANGER|
|H225, H300, H311, H314, H330, H351, H411|
|P210, P260, P273, P280, P284|
|Flash point||−8 °C; 17 °F; 265 K |
|196 °C (385 °F; 469 K)|
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
|32 mg kg−1 (oral, rat)|
LC50 (median concentration)
|34 ppm (rat, 4 hr)|
74 ppm (rat, 4 hr)
162 ppm (monkey, 1 hr)
195 ppm (dog, 30 min)
145 ppm (monkey, 30 min)
272 ppm (mouse, 30 min)
427 ppm (rat, 30 min)
56 ppm (mouse, 4 hr)
143 ppm (hamster, 4 hr)
|US health exposure limits (NIOSH):|
|C 0.2 ppm (0.35 mg/m3) [skin]|
|Ca C 0.04 ppm (0.08 mg/m3) [2-hr]|
IDLH (Immediate danger)
|Ca [20 ppm]|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).