Methyl yellow

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Methyl yellow

IUPAC name	p-Dimethylaminoazobenzene
Other names	4-Dimethylaminoazobenzene, N,N-Dimethyl-4-phenylazoaniline, N,N-Dimethyl-4-aminoazobenzene, Butter Yellow, Solvent Yellow 2, C.I. 11020
Identifiers
CAS number	[60-11-7]
PubChem	6053
EINECS number	200-455-7
RTECS number	BX7350000
SMILES	CN(C)C(C=C2)=CC=C2N=NC1=CC=CC=C1
Properties
Molecular formula	C₁₄H₁₅N₃
Molar mass	225.289 g.mol^-1
Appearance	Yellow crystals
Melting point	116 °C (decomp.)
Solubility in water	13.6 mg.l^-1
log P	4.58
Hazards
Main hazards	Toxic (T)
NFPA 704	1 2 0
R-phrases	R25, R40
S-phrases	S36/37, S45
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Methyl yellow, or C.I. 11020, is a chemical compound which may be used as a pH indicator.

Methyl yellow (pH indicator)
below pH 2.9		above pH 4.0
2.9	↔	4.0

In aqueous solution at low pH, methyl yellow appears red. Between pH 2.9 and 4.0, methyl yellow undergoes a transition, to become yellow above pH 4.0.

Additional indicators are listed in the article on pH indicators.

As "butter yellow" the agent had been used as a food additive before its toxicity was recognized (Opie EL)

[edit] References

NIOSH Pocket Guide to Chemical Hazards 0220
Eugene L. Opie. The Pathogenesis of Tumors of the Liver Produced by Butter Yellow. The Journal of Experimental Medicine, Vol 80, 231-246, 1944.