Title: Azolitmin
CAS Registry Number: 1395-18-2
Literature References: Purified coloring matter from litmus: I. M. Kolthoff, C. Rosenblum, Acid-Base Indicators (MacMillan Co., New York, 1937) pp 160-162, 174, 208, 355, 361, 365-366, 368-369, 373, 377, 387.
Properties: Dark violet scales or dark red powder. Sparingly soluble in water; insol in alc; freely sol in dil alkali hydroxides or carbonates. The indicator solution is prepared by dissolving 0.5 g in 80 ml of warm H2O, then adding 20 ml alcohol.
Use: Indicator instead of litmus. pH: 4.5 red, 8.3 blue. Usable with most mineral, some organic acids (not hydroxy acids) and some alkaloids; also used for preparing litmus media for bacteriologic purposes.
Azomycin Azosemide Azoxybenzene Azoxystrobin Aztreonam

Litmus powder
Chemical structure of 7-hydroxyphenoxazone, the chromophore of litmus components

Litmus is a water-soluble mixture of different dyes extracted from lichens, especially Roccella tinctoria. It is often absorbed onto filter paper to produce one of the oldest forms of pH indicator, used to test materials for acidity. Blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic (i.e. alkaline) conditions, with the color change occurring over the pH range 4.5-8.3 at 25 °C. Neutral litmus paper is purple.[1] Litmus can also be prepared as an aqueous solution that functions similarly. Under acidic conditions the solution is red, and under basic conditions the solution is blue.

The litmus mixture has the CAS number 1393-92-6 and contains 10 to 15 different dyes. Most of the chemical components of litmus are likely to be the same as those of the related mixture known as orcein, but in different proportions. In contrast with orcein, the principal constituent of litmus has average molecular weight of 3300.[2] Acid-base indicators on litmus owe their properties to a 7-hydroxyphenoxazone chromophore.[3] Some fractions of litmus were given specific names including erythrolitmin (or erythrolein), azolitmin, spaniolitmin, leucoorcein and leucazolitmin. Azolitmin shows nearly the same effect as litmus.[4]