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3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||60.1 g/mol|
|Melting point||−57 °C (−71 °F; 216 K)|
|Boiling point||63 °C (145 °F; 336 K)|
|Toxic (T), Flammable (F), Harmful for the environment (N)|
|R-phrases (outdated)||R45 R11 R23/25 R34 R51/53|
|S-phrases (outdated)||S53 S45 S61|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Unsymmetrical dimethylhydrazine (UDMH) (1,1-Dimethylhydrazine) is a toxic volatile hygroscopic clear liquid, with a sharp, fishy, ammoniacal smell typical for organic amines. It turns yellowish on exposure to air and absorbs oxygen and carbon dioxide. It mixes completely with water, ethanol, and kerosene. In concentration between 2.5% and 95% in air, its vapors are flammable. It is not sensitive to shock.
UDMH is often used in hypergolic rocket fuels as a bipropellant in combination with the oxidizer nitrogen tetroxide and less frequently with IRFNA (red fuming nitric acid) or liquid oxygen. UDMH is a derivative of hydrazine and is sometimes referred to as a hydrazine. As a fuel, it is described in specification MIL-D-25064.
UDMH is stable and can be kept loaded in rocket fuel systems for long periods, which makes it appealing for use in many liquid rocket engines, despite its high density and cost. In some applications, such as the OMS in the Space Shuttle or maneuvering engines, monomethylhydrazine is used instead due to its slightly higher specific impulse. UDMH functions as a starter fuel to start combustion and warm the rocket engine prior to switching to kerosene. UDMH has higher stability than hydrazine, especially at elevated temperatures, and can be used as its replacement or together in a mixture. UDMH is used in many European, Russian, Indian, and Chinese rocket designs. The Titan, GSLV, and Delta rocket families use a mixture of 50% hydrazine and 50% UDMH, called Aerozine 50, in different stages.
UDMH is toxic, a carcinogen and can explode in the presence of oxidisers. It is toxic and is absorbed through the skin. During the 1980s there was concern about the levels of UDMH in various foods being a cancer risk, especially for apple juice.
- UDMH released into the environment can react in air to form dimethylnitrosamine, a persistent carcinogen and groundwater pollutant. "Are pesticides posing intolerable risks?". Cornell University.