Methyl Red Indicator ACS, Ph Eur C.I. 13020

C.I. 13020  (Acid Red 2)

Methyl red (2-(N,N-Dimethyl-4-aminophenyl)azobenzenecarboxylic acid), also called C.I. Acid Red 2, is an indicator dye that turns red in acidic solutions. It is an azo dye, and is a dark red crystalline powder. Methyl red is a pH indicator; it is red in pH under 4.4, yellow in pH over 6.2, and orange in between, with a pKa of 5.1.

• pH Indicator
• Identification of bacteria in Microbiology

C.I. 13020

Molecular Formula: C₁₅H₁₅N₃O₂ 
Molecular Weight: 269.30
Melting Point: 179-182 deg C
Absorption Min (pH 4.5 Buffer): 523-526nm
Absorption Max (pH 4.5 Buffer): 427-437nm
Specific Absorptivity (A1%/1cm): 1350-1450 (0.005g/L Buffer pH 4.5)
Specific Absorptivity (A1%/1cm): 700-800 (0.005g/L Buffer pH 6.2)
Transition Range: pH 4.4-6.0 (Red-Yellow)
Loss on Drying (110degC): <5%

Cas Number: 493-52-7

Einecs Number: 207-776-1

HS Code / Commodity Code: 29270000