Neutral red

Neutral red
IUPAC name	toluylene red
Identifiers
CAS number	553-24-2 Y
SMILES	CC3=CC2=NC1=CC=C (N(C)C)C=C1N C2=C/C3=[N+](C)/C
Properties
Molecular formula	C15H17ClN4
Molar mass	288.78 g/mol
Melting point	290°C
Boiling point	°C
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Neutral Red (or toluylene red, Basic Red 5, or C.I. 50040) is a eurhodin dye used for staining in histology. It stains lysosomes red ^[1]. It is used as a general stain in histology, as a counterstain in combination with other dyes, and for many staining methods. Together with Janus Green B it is used to stain embryonal tissues and supravital staining of blood. Can be used for staining Golgi apparatus in cells and Nissl granules in neurons.

Neutral red can be used as a vital stain, to stain living cells. It is used to stain cell cultures for plate titration of viruses.

Neutral Red is added to some growth media for bacteria and cell cultures. It usually comes as a chloride salt.

Neutral Red acts as a pH indicator, changing from red to yellow between the pH 6.8-8.0.

Practical Joke Uses

It's claimed that Neutral Red turns human urine red. The Wiretap Practical Joke Archive details doctoring red wine with Neutral Red to convince the subject they are urinating blood. Neutral red's tendency to turn from red to yellow between the pH 6.8-8.0 throws doubt on the validity of this claim, as the pH of urine is often 5.5-7.0 to become red, the pH of 8 will cause the color be yellow. Hence, it might not work every time.

There are similar claims about Methylene Blue.

References

1. ^ Winckler, J. Vital staining of lysosomes and other cell organelles of the rat with neutral Red. Prog. Histochem. Cytochem. 6, 1–89 (1974).