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Ball-and-stick model of phenylhydrazine
Space-filling model of phenylhydrazine
IUPAC name
Other names
3D model (JSmol)
ECHA InfoCard 100.002.612
Molar mass 108.14 g/mol
Appearance Colorless to pale-yellow liquid or solid[3]
Odor faint, aromatic[3]
Density 1.0978 g/cm3
Melting point 19.5 °C (67.1 °F; 292.6 K) (24 °C for hemihydrate)
Boiling point 243.5 °C (470.3 °F; 516.6 K) (decomposition)
Vapor pressure 0.04 mmHg (25°C)[3]
-67.82·10−6 cm3/mol
NFPA 704 (fire diamond)
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelHealth code 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity code 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g. hydrogen peroxideSpecial hazards (white): no codeNFPA 704 four-colored diamond
Flash point 88 °C; 190 °F; 361 K [3]
Lethal dose or concentration (LD, LC):
188 mg/kg (rat, oral)
175 mg/kg (mouse, oral)
80 mg/kg (rabbit, oral)
80 mg/kg (guinea pig, oral)
200-250 mg/kg (dog, oral)[4]
NIOSH (US health exposure limits):
PEL (Permissible)
TWA 5 ppm (22 mg/m3) [skin][3]
REL (Recommended)
Ca C 0.14 ppm (0.6 mg/m3) [2-hr] [skin][3]
IDLH (Immediate danger)
Ca [15 ppm][3]
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

Phenylhydrazine is the chemical compound with the formula C6H5NHNH2. It is often abbreviated as PhNHNH2.


Phenylhydrazine forms monoclinic prisms that melt to an oil around room temperature which may turn yellow to dark red upon exposure to air.[1] Phenylhydrazine is miscible with ethanol, diethyl ether, chloroform and benzene. It is sparingly soluble in water.


Phenylhydrazine is prepared by oxidizing aniline with sodium nitrite in the presence of hydrogen chloride to form the diazonium salt, which is subsequently reduced using sodium sulfite in the presence of sodium hydroxide to form the final product.[5]


Phenylhydrazine was the first hydrazine derivative characterized, reported by Hermann Emil Fischer in 1875.[6][7] He prepared it by reduction of a phenyl diazonium salt using sulfite salts. Fischer used phenylhydrazine to characterize sugars via formation of hydrazones with the sugar aldehyde. He also demonstrated in this first paper many of the key properties recognized for hydrazines.


Phenyl-hydrazine is used to prepare indoles by the Fischer indole synthesis, which are intermediates in the synthesis of various dyes and pharmaceuticals.

Phenylhydrazine is used to form phenylhydrazones of natural mixtures of simple sugars in order to render the differing sugars easily separable from each other.[8]

This molecule is also used to induce acute hemolytic anemia in animal models.


Exposure to phenylhydrazine may cause contact dermatitis, hemolytic anemia, and liver damage.[1]


  1. ^ a b c Merck Index, 11th Edition, 7264.
  2. ^ Pure component properties
  3. ^ a b c d e f g NIOSH Pocket Guide to Chemical Hazards. "#0499". National Institute for Occupational Safety and Health (NIOSH).
  4. ^ "Phenylhydrazine". Immediately Dangerous to Life and Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  5. ^ Merck Index of Chemicals and Drugs, 9th ed. monograph 7098
  6. ^ Nobel Committee Emil Fischer - Biographical
  7. ^ Fischer, E. (1875) "Ueber aromatische Hydrazinverbindungen," Berichte der deutschen chemischen Gesellschaft, 8: 589-594.
  8. ^ Andrew Streitwieser; Clayton Heathcock (1976). Introduction to Organic Chemistry. Macmillan. ISBN 0-02-418010-6.

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