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Title: Phenylhydrazine  
Author: World Heritage Encyclopedia
Language: English
Subject: Osazone, Hydrazines, Krikor Pambuccian, Pyridazine, Carbazole
Collection: Aromatic Compounds, Hydrazines, Monoamine Oxidase Inhibitors
Publisher: World Heritage Encyclopedia


Ball-and-stick model of phenylhydrazine
Space-filling model of phenylhydrazine
IUPAC name
Other names
ChemSpider  Y
Jmol-3D images Image
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; 292.7 K) (24 °C for hemihydrate)
Boiling point 243.5 °C (470.3 °F; 516.7 K) (decomposition)
Vapor pressure 0.04 mmHg (25°C)[3]
NFPA 704
Flash point 88 °C; 190 °F; 361 K [3]
Lethal dose or concentration (LD, LC):
LD50 (Median dose)
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]
US health exposure limits (NIOSH):
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]
Ca [15 ppm][3]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
 Y  (: Y/N?)

Phenylhydrazine is the chemical compound with the formula C6H5NHNH2. Organic chemists abbreviate the compound as PhNHNH2.


  • Chemical properties 1
  • Preparation 2
  • History 3
  • Uses 4
  • Safety 5
  • See also 6
  • References 7
  • External links 8

Chemical properties

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 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.


Phenylhydrazine is used to prepare indoles via 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]

The compound is also used to induce acute hemolytic anemia in studies examining the hematopoietic system.


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

See also


  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".  
  4. ^ "Phenylhydrazine". Immediately Dangerous to Life and Health.  
  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. ^  

External links

  • Phenylhydrazines at the US National Library of Medicine Medical Subject Headings (MeSH)
  • PubChem
  • Additional chemical properties of phenylhydrazine
  • CDC - NIOSH Pocket Guide to Chemical Hazards
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