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Unsymmetrical dimethylhydrazine

Unsymmetrical dimethylhydrazine
Skeletal formula of unsymmetrical dimethylhydrazine with some implicit hydrogens shown
Ball and stick model of unsymmetrical dimethylhydrazine
Names
IUPAC name
1,1-dimethylhydrazine
Other names
Dimazine
Identifiers
3D model (Jmol)
605261
ChEBI
ChemSpider
ECHA InfoCard 100.000.287
EC Number 200-316-0
KEGG
MeSH dimazine
PubChem CID
RTECS number MV2450000
UN number 1163
Properties
C2H8N2
Molar mass 60.10 g·mol−1
Appearance Colourless liquid
Odor Ammoniacal, fishy
Density 791 kg m−3 (at 22 °C)
Melting point −57 °C; −71 °F; 216 K
Boiling point 64.0 °C; 147.1 °F; 337.1 K
miscible
Vapor pressure 13.7 kPa (at 20 °C)
1.4075
Thermochemistry
164.05 J K−1 mol−1
200.25 J K−1 mol−1
48.3 kJ mol−1
−1982.3–−1975.1 kJ mol−1
Hazards
Main hazards carcinogen, spontaneously ignites on contact with oxidizers
GHS pictograms The flame pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The corrosion pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The skull-and-crossbones pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The health hazard pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The environment pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word DANGER
H225, H301, H314, H331, H350, H411
P210, P261, P273, P280, P301+310
Highly Flammable F Toxic T Dangerous for the Environment (Nature) N
R-phrases R45, R11, R23/25, R34, R51/53
NFPA 704
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g., gasoline) Health code 4: Very short exposure could cause death or major residual injury. E.g., VX gas Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point −10 °C (14 °F; 263 K)
248 °C (478 °F; 521 K)
Explosive limits 2–95%
Lethal dose or concentration (LD, LC):
LD50 (median dose)
  • 122 mg kg−1(oral, rat)
  • 1.06 g kg−1(dermal, rabbit)
252 ppm (rat, 4 hr)
172 ppm (mouse, 4 hr)
392 ppm (hamster, 4 hr)
3580 ppm (dog, 15 min)
1410 ppm (rat, 1 hr)
981 ppm (dog, 1 hr)
US health exposure limits (NIOSH):
PEL (Permissible)
 TWA 0.5 ppm (1 mg/m3) [skin]
REL (Recommended)
 Ca C 0.06 ppm (0.15 mg/m3) [2-hr]
IDLH (Immediate danger)
 Ca [15 ppm]
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Unsymmetrical dimethylhydrazine (UDMH; 1,1-dimethylhydrazine) is a chemical compound with the formula H2NN(CH3)2. It is a colourless liquid, with a sharp, fishy, ammoniacal smell typical for organic amines. Samples turn yellowish on exposure to air and absorb 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. 1,2-Dimethylhydrazine (CH3NHNH(CH3)) is also known but is not as useful.

UDMH is produced industrially by two routes. One, based on the Olin Raschig process, involves reaction of chloramine with dimethylamine. This method gives the hydrochloride of the hydrazine:

Alternatively, acetylhydrazine can be N-methylated using formaldehyde to give the N,N-dimethyl-N'-acetylhydrazine, which can subsequently be hydrolyzed:

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-PRF-25604.

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 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. In some kerosene-fueled rockets, 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 Russian Proton, Kosmos-3M, and the Chinese Long March 2F are the most notable users of UDMH (which is referred to as "heptyl" by Russian engineers). The Titan, GSLV, and Delta rocket families use a mixture of 50% hydrazine and 50% UDMH, called Aerozine 50, in different stages.


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