Unsymmetrical dimethylhydrazine

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Unsymmetrical dimethylhydrazine
Skeletal formula of unsymmetrical dimethylhydrazine with some implicit hydrogens shown
Ball and stick model of unsymmetrical dimethylhydrazine
Identifiers
CAS number 57-14-7 YesY
PubChem 5976
ChemSpider 5756 N
EC number 200-316-0
UN number 1163
KEGG C19233 YesY
MeSH dimazine
ChEBI CHEBI:18853 N
RTECS number MV2450000
Beilstein Reference 605261
Jmol-3D images Image 1
Properties
Molecular formula C2H8N2
Molar mass 60.10 g mol−1
Appearance Colourless liquid
Odor Ichtyal, ammoniacal
Density 790 mg mL−1 (at 20 °C)
Melting point −57 °C; −71 °F; 216 K
Boiling point 64.0 °C; 147.1 °F; 337.1 K
Vapor pressure 13.7 kPa (at 20 °C)
Refractive index (nD) 1.4075
Thermochemistry
Specific
heat capacity
C
164.05 J K−1 mol−1
Std molar
entropy
So298
200.25 J K−1 mol−1
Std enthalpy of
formation
ΔfHo298
48.3 kJ mol−1
Std enthalpy of
combustion
ΔcHo298
−1982.3–−1975.1 kJ mol−1
Hazards
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
GHS hazard statements H225, H301, H314, H331, H350, H411
GHS precautionary statements P210, P261, P273, P280, P301+310
EU Index 007-012-00-5
EU classification 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)
Explosive limits 2–95%
LD50
  • 122 mg kg−1 (oral, rat)
  • 1.06 g kg−1 (dermal, rabbit)
Related compounds
Related compounds
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
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. Symmetrical dimethylhydrazine (CH3NHNH(CH3)) is also known but is not as useful.[2]

Production[edit]

UDMH is produced industrially by two routes.[2] One, based on the Olin Raschig process, involves reaction of chloramine with dimethylamine. This method gives the hydrochloride of the hydrazine:

(CH3)2NH + NH2Cl → (CH3)2NNH2 + HCl

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

CH3C(O)NHNH2 + 2 CH2O + 2 H2 → CH3C(O)NHN(CH3)2 + 2 H2O
CH3C(O)NHN(CH3)2 + H2O → CH3COOH + H2NN(CH3)2

Uses[edit]

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.[3]

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[4]). The Titan, GSLV, and Delta rocket families use a mixture of 50% hydrazine and 50% UDMH, called Aerozine 50, in different stages.[5]

Apart from its use as rocket fuel, UDMH is a nitrogen source in metalorganic vapour phase epitaxy thin-film deposition.[citation needed] UDMH is a contaminant, metabolite, and breakdown product of daminozide.[citation needed]

Safety[edit]

UDMH is toxic, a carcinogen and can explode in the presence of oxidisers. It can be absorbed through 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.[6]

See also[edit]

References[edit]

  1. ^ "dimazine - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 26 March 2005. Identification. Retrieved 21 February 2012. 
  2. ^ a b Jean-Pierre Schirmann, Paul Bourdauducq "Hydrazine" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2002. doi:10.1002/14356007.a13_177.
  3. ^ MIL-PRF-25604 (1997-10-01). "Performance Specification, Propellant, uns-Dimethylhydrazine". Retrieved 2011-05-21. 
  4. ^ "Following Russian rocket explosion, experts warn of 'major contamination'". 
  5. ^ Clark, John D. (1972). Ignition! An Informal History of Liquid Rocket Propellants. Rutgers University Press. p. 45. ISBN 0-8135-0725-1. 
  6. ^ "Are pesticides posing intolerable risks?". Cornell University. 

External links[edit]