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| Names | |||
|---|---|---|---|
| Preferred IUPAC name 1,1-Dimethylhydrazine[1] | |||
| Other names Dimazine 1,1-Dimethyldiazane | |||
| Identifiers | |||
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3D model (JSmol) | |||
| 605261 | |||
| ChEBI | |||
| ChemSpider |
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| ECHA InfoCard | 100.000.287 | ||
| EC Number |
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| KEGG |
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| MeSH | dimazine | ||
| RTECS number |
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| UNII | |||
| UN number | 1163 | ||
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| 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) | ||
Refractive index (nD) | 1.4075 | ||
| Thermochemistry | |||
| 164.05 J K−1 mol−1 | |||
Std molar entropy(S⦵298) | 200.25 J K−1 mol−1 | ||
Std enthalpy of formation(ΔfH⦵298) | 48.3 kJ mol−1 | ||
Std enthalpy of combustion(ΔcH⦵298) | −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: | |||
     | |||
| Danger | |||
| H225,H301,H314,H331,H350,H411 | |||
| P210,P261,P273,P280,P301+P310 | |||
| NFPA 704 (fire 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) |
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LC50 (median concentration) |
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| 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 theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Unsymmetrical dimethylhydrazine (abbreviated asUDMH; also known as1,1-dimethylhydrazine,heptyl orGeptil) is achemical compound with the formula H2NN(CH3)2 that is primarily used as arocket propellant.[4] At room temperature, UDMH is a colorless liquid, with a sharp, fishy, ammonia-like smell typical of organicamines. Samples turn yellowish on exposure to air and absorboxygen andcarbon dioxide. It ismiscible with water,ethanol, andkerosene. At concentrations between 2.5% and 95% in air, its vapors are flammable. It is not sensitive to shock.
Symmetrical dimethylhydrazine (1,2-dimethylhydrazine) also exists, but it is not as useful.[5] UDMH can be oxidized in air to form many different substances, including toxic ones.[6][7][8]
In 1875, UDMH was first prepared byEmil Fischer, who discovered and named the class ofhydrazines, by reducingN-Nitrosodimethylamine with zinc in boilingacetic acid.[9][10] Fischer's studentEdward Renouf later studied UDMH more extensively as part of his doctoral dissertation. Other historical lab routes includemethylation ofhydrazine, reduction of nitrodimethylamine andamination ofdimethylamine with aminopersulfuric acid.[11]
UDMH is produced industrially by two routes.[5] Based on theOlin Raschig process, one method involves reaction ofmonochloramine withdimethylamine giving 1,1-dimethylhydrazinium chloride:
In the presence of suitable catalysts, acetylhydrazine can be N-dimethylated usingformaldehyde and hydrogen to give the N,N-dimethyl-N'-acetylhydrazine, which can subsequently be hydrolyzed:
UDMH is often used inhypergolicrocket fuels as abipropellant in combination with the oxidizernitrogen tetroxide and less frequently withIRFNA (inhibited red fuming nitric acid) orliquid oxygen.[12] UDMH is a derivative ofhydrazine and is sometimes referred to as a hydrazine. As a fuel, it is described in specification MIL-PRF-25604 in the United States.[13]
UDMH is stable and can be kept loaded in rocket fuel systems for long periods, which makes it appealing for use in manyliquid rocket engines, despite its cost. In some applications, such as the OMS in theSpace Shuttle ormaneuvering engines,monomethylhydrazine is used instead due to its slightly higherspecific 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 RussianSS-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 ChineseLong March 2 are the most notable users of UDMH (which is referred to as "heptyl" (codename fromSoviet era)[citation needed] by Russian engineers[14]). TheTitan,GSLV, andDelta rocket families use a mixture of 50% hydrazine and 50% UDMH, calledAerozine 50, in different stages.[15] There is speculation that it is the fuel used in the ballistic missiles that North Korea has developed and tested in 2017.[16]
Hydrazine and its methyl derivatives are toxic butLD50 values have not been reported.[17] It is a precursor todimethylnitrosamine, which is carcinogenic.[18]According to scientific data, usage of UDMH in rockets atBaikonur Cosmodrome has had adverse effects on the environment.[19]One such instance was theNedelin catastrophe in 1960 when UDMH anddinitrogen tetroxide leaked from a rocket after an explosion and killed a number of bystanders through burn injuries and its toxicity.
