Unsymmetrical dimethylhydrazine explained

Unsymmetrical dimethylhydrazine (UDMH; 1,1-dimethylhydrazine, heptyl or codenamed Geptil) is a chemical compound with the formula H2NN(CH3)2 that is used as a rocket propellant.[1] 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. UDMH can be oxidized in air to form many different substances, including toxic ones.[2] [3] [4]

Production

UDMH is produced industrially by two routes. 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.[5] 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.[12]

See also

External links

Notes and References

  1. Semenkov . Ivan . Koroleva . Tatyana . 1 December 2022 . Review on the environmental impact of emissions from space launches: a case study for areas affected by the Russian space programme . Environmental Science and Pollution Research . en . 29 . 60 . 89807–89822 . 10.1007/s11356-022-23888-8 . 36346528 . 2022ESPR...2989807S . 253396676 . 1614-7499.
  2. Unsymmetrical dimethylhydrazine transformation products: A review. Aleksey Milyushkin, Anastasia Karnaeva. Science of the Total Environment. 891. 2023. 164367. 10.1016/j.scitotenv.2023.164367. 37236454. 2023ScTEn.89164367M. 258899003.
  3. Ul'yanovskii . Nikolay V. . Lakhmanov . Dmitry E. . Pikovskoi . Ilya I. . Falev . Danil I. . Popov . Mark S. . Kozhevnikov . Alexander Yu. . Kosyakov . Dmitry S. . 15 July 2020 . Migration and transformation of 1,1-dimethylhydrazine in peat bog soil of rocket stage fall site in Russian North . Science of the Total Environment . 726 . 138483 . 10.1016/j.scitotenv.2020.138483 . 32315849 . 2020ScTEn.72638483U . 216073493 . 0048-9697.
  4. Koroleva . T. V. . Semenkov . I. N. . Lednev . S. A. . Soldatova . O. S. . 1 February 2023 . Unsymmetrical Dimethylhydrazine (UDMH) and Its Transformation Products in Soils: A Review of the Sources, Detection, Behavior, Toxicity, and Remediation of Polluted Territories . Eurasian Soil Science . en . 56 . 2 . 210–225 . 10.1134/S1064229322602001 . 2023EurSS..56..210K . 257903133 . 1556-195X.
  5. Semenkov . Ivan . Koroleva . Tatyana . 1 December 2022 . Review on the environmental impact of emissions from space launches: a case study for areas affected by the Russian space programme . Environmental Science and Pollution Research . en . 29 . 60 . 89807–89822 . 10.1007/s11356-022-23888-8 . 36346528 . 2022ESPR...2989807S . 253396676 . 1614-7499.
  6. Web site: PERFORMANCE SPECIFICATION PROPELLANT, uns-DIMETHYLHYDRAZINE (MIL-PRF-25604F). 11 March 2014. ASSIST Database Quicksearch. 26 May 2020.
  7. Web site: Following Russian rocket explosion, experts warn of 'major contamination'. 2 July 2013.
  8. Book: Clark, John D. . John Drury Clark . Ignition! An Informal History of Liquid Rocket Propellants . Rutgers University Press . 1972 . 45 . 0-8135-0725-1 .
  9. News: The Rare, Potent Fuel Powering North Korea's Weapons. William J.. Broad. David E.. Sanger. The New York Times. 17 September 2017.
  10. Web site: 4 . unsym-Dimethylhydrazine Safedy data . 23 January 2018 . 6 July 2018 . https://web.archive.org/web/20180706161800/https://www.fishersci.com/shop/msdsproxy?productName=AC116320100&productDescription=UNSYM-DIMETHYLHYDRAZINE%252C+10ML&catNo=AC116320100&vendorId=VN00032119&storeId=10652 . dead .
  11. Human health perspective of environmental exposure to hydrazines: A review. Gangadhar Choudhary, Hugh Hansen. Chemosphere. 37. 1998. 5. 801–843. 10.1016/S0045-6535(98)00088-5. 9717244. 1998Chmsp..37..801C.
  12. The impact of the cosmodrome 'Baikonur' on the environment and human health. P. Kh. Abdrazak. K. Sh. Musa. 21 June 2015. 8. 1. 26–29. 2 August 2016. ijbch.kaznu.kz. International Journal of Biology and Chemistry. 10.26577/2218-7979-2015-8-1-26-29 . 8 August 2016. https://web.archive.org/web/20160808090550/http://ijbch.kaznu.kz/index.php/kaznu/article/view/172. live. free.

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