Unsymmetrical dimethylhydrazine

Unsymmetrical dimethylhydrazine (UDMH; 1,1-dimethylhydrazine, НДМГ; Несимметричный диметилгидразин (NDMG / NDMH or codenamed гептил heptil) is a chemical compound with the formula H2NN(CH3)2 that is used as a rocket propellant. It is a colorless liquid, with a sharp, fishy, ammonia-like smell typical for organic amines. Samples turn yellowish on exposure to air and absorb oxygen and carbon dioxide. It is miscible 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, 1,2-dimethylhydrazine is also known but is not as useful.[4] UDMH can be oxidized in air to form many different substances, including toxic ones.[5]

Unsymmetrical dimethylhydrazine
Skeletal formula of unsymmetrical dimethylhydrazine with some implicit hydrogens shown
Ball and stick model of unsymmetrical dimethylhydrazine
Names
Preferred IUPAC name
1,1-Dimethylhydrazine[1]
Other names
Dimazine
Identifiers
3D model (JSmol)
605261
ChEBI
ChemSpider
ECHA InfoCard 100.000.287
EC Number
  • 200-316-0
KEGG
MeSH dimazine
RTECS number
  • MV2450000
UNII
UN number 1163
  • InChI=1S/C2H8N2/c1-4(2)3/h3H2,1-2H3 ☒N
    Key: RHUYHJGZWVXEHW-UHFFFAOYSA-N ☒N
  • CN(C)N
Properties
H2NN(CH3)2
Appearance Colorless 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[2]
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
Occupational safety and health (OHS/OSH):
Main hazards
 Carcinogen, spontaneously ignites on contact with oxidizers
GHS labelling:
GHS02: Flammable GHS05: Corrosive GHS06: Toxic GHS08: Health hazard GHS09: Environmental hazard
Danger
H225, H301, H314, H331, H350, H411
P210, P261, P273, P280, P301+P310
NFPA 704 (fire diamond)
NFPA 704 four-colored diamond
4
3
1
Flash point −10 °C (14 °F; 263 K)
248 °C (478 °F; 521 K)
Explosive limits 2–95%
Lethal dose or concentration (LD, LC):
  • 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)[3]
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 0.5 ppm (1 mg/m3) [skin][2]
REL (Recommended)
 Ca C 0.06 ppm (0.15 mg/m3) [2 hr][2]
IDLH (Immediate danger)
 Ca [15 ppm][2]
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

Production

UDMH is produced industrially by two routes.[4] Based on the Olin Raschig process, one method involves reaction of monochloramine with dimethylamine giving 1,1-dimethylhydrazinium chloride:

(CH3)2NH + NH2Cl → (CH3)2NNH2 ⋅ HCl

In the presence of suitable catalysts, acetylhydrazine can be N-dimethylated using formaldehyde and hydrogen to give the N,N-dimethyl-N'-acetylhydrazine, which can subsequently be hydrolyzed:

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

Uses

UDMH is often used in hypergolic rocket fuels as a bipropellant in combination with the oxidizer nitrogen tetroxide and less frequently with IRFNA (inhibited 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 in the United States.[6]

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 SS-11 Sego (aka 8K84) ICBM, SS-19 Stiletto (aka 15A30) ICBM, Proton, Kosmos-3M, R-29RMU2 Layner, R-36M, Rokot (based on 15A30) and the Chinese Long March 2F are the most notable users of UDMH (which is referred to as "heptyl" [codename from Soviet era] by Russian engineers[7]). The Titan, GSLV, and Delta rocket families use a mixture of 50% hydrazine and 50% UDMH, called Aerozine 50, in different stages.[8] There is speculation that it is the fuel used in the ballistic missiles that North Korea has developed and tested in 2017.[9]

Safety

Hydrazine and its methyl derivatives are toxic but LD50 values have not been reported.[10] It is a precursor to dimethylnitrosamine, which is carcinogenic.[11] According to scientific data, usage of UDMH in rockets at Baikonur Cosmodrome has had adverse effects on the environment and local population.[12]

See also

References
  1. "dimazine – Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 26 March 2005. Identification. Retrieved 21 February 2012.
  2. NIOSH Pocket Guide to Chemical Hazards. "#0227". National Institute for Occupational Safety and Health (NIOSH).
  3. "1,1-Dimethylhydrazine". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  4. Schirmann, Jean-Pierre; Bourdauducq, Paul (2001). "Hydrazine". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a13_177.
  5. Aleksey Milyushkin, Anastasia Karnaeva (2023). "Unsymmetrical dimethylhydrazine transformation products: A review". Science of the Total Environment. 891: 164367. Bibcode:2023ScTEn.891p4367M. doi:10.1016/j.scitotenv.2023.164367. PMID 37236454. S2CID 258899003.
  6. "PERFORMANCE SPECIFICATION PROPELLANT, uns-DIMETHYLHYDRAZINE (MIL-PRF-25604F)". ASSIST Database Quicksearch. 2014-03-11. Retrieved 2020-05-26.
  7. "Following Russian rocket explosion, experts warn of 'major contamination'". 2 July 2013.
  8. Clark, John D. (1972). Ignition! An Informal History of Liquid Rocket Propellants. Rutgers University Press. p. 45. ISBN 0-8135-0725-1.
  9. Broad, William J.; Sanger, David E. (17 September 2017). "The Rare, Potent Fuel Powering North Korea's Weapons". The New York Times.
  10. "Archived copy". Archived from the original on 2018-07-06. Retrieved 2018-07-06.{{cite web}}: CS1 maint: archived copy as title (link)
  11. Gangadhar Choudhary, Hugh Hansen (1998). "Human health perspective of environmental exposure to hydrazines: A review". Chemosphere. 37 (5): 801–843. Bibcode:1998Chmsp..37..801C. doi:10.1016/S0045-6535(98)00088-5. PMID 9717244.
  12. Abdrazak, P. Kh; Musa, K. Sh (21 June 2015). "The impact of the cosmodrome "Baikonur" on the environment and human health". International Journal of Biology and Chemistry. 8 (1): 26–29. doi:10.26577/2218-7979-2015-8-1-26-29. Archived from the original on 8 August 2016. Retrieved 2 August 2016 – via ijbch.kaznu.kz.
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