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Neutral Red

Neutral Red

Class: Eurhodin
Ionisation: Basic

Chemical structure of Neutral Red

Common Name: Neutral red
Suggested Name: Neutral red
Other Names:

Toluylene red Toluylene redNuclear fast red Toluylene redNuclear fast redKernechtrot

C.I. Number: 50040
C.I. Name: Basic red 5
Color: Red
Solubility Aqueous: 5.6% (Conn) 4% (Merck)
Solubility Ethanol: 5.6% (Conn) 4% (Merck)
Absorption Maximum: 540-542 (Conn) 533 (Merck) 529 (Gurr)
Empirical Formula: C15H17N4Cl
Formula Weight: 288.8


This dye has been widely used in many staining methods, but its commonest use is probably as a simple red nuclear counterstain. It is an indicator as well as a dye. It changes from red to yellow over the pH range 6.8 - 8.0. It has also been incorporated into bacteriological growth media.

The Merck Index gives the names nuclear fast red and kernechtrot as synonyms for neutral red. These two names are usually applied to another dye, CI 60760, which can be used as a red nuclear stain when mordanted with potassium alum. If a technique calls for nuclear fast red or kernechtrot, it is probably this latter dye to which it refers, not neutral red.


  1. R. D. Lillie.
    Conn’s Biological Stains
    Williams & Wilkins, Baltimore, MD., U.S.A.
  2. Aldrich chemical catalogue, 1992
    Aldrich Chemical Company, Milwaukee, WI, USA.
  3. Edward Gurr, 1971
    Synthetic dyes in biology, medicine and chemistry
    Academic Press, London, England.
  4. Susan Budavari, Editor,
    The Merck Index, Ed. 12
    Merck & Co., Inc., Whitehouse Station, NJ, USA