Methylorange
- Sodium -4-( dimethylamino) - azobenzene -4' -sulfonic acid
- Helianthin
- Orange III
- Gold Orange
- Tropaeolin D
- C. I. 13025
- C. I. Acid Orange 52
Orange solid
Fixed
1.28 g · cm -3
> 300 ° C
Poorly in water (approximately 5 g · l -1)
Risk
60 mg · kg -1 ( LD50, rat, oral)
Template: Infobox chemical / molecular formula search available
Methyl orange belongs to the group of azo dyes. It is the sodium salt of 4'-( dimethylamino) -azobenzene -4 -sulfonic acid and is most commonly used as a pH indicator.
Properties
Methyl orange is orange crystals. In a strongly acidic pH range, the azo group is protonated. In addition, the base group is deprotonated in the pH range from 3.1 to 4.4 and there is a color change from red to yellow orange.
Use
Methyl orange is used as the acid-base indicator.
Synthesis
Sulfanilic acid is diazotized with nitrous acid and then converted to 4- Benzoldiazoniumsulfonsäure:
Then the 4- Benzoldiazoniumsulfonsäure with N, N -dimethylaniline (green) is coupled and transferred to the sodium salt with sodium hydroxide solution and precipitated:
The resulting sodium salt - at the same time, an azo dye - is methyl orange.