Indigo red, molecular formula: c8h5no2, molecular weight: 147.13, is used for the preparation of vat dyes and drugs, and also used for the analysis of cuprous ions, mercaptans, thiophene, and indosine. It is also known as indoleanedione; indolinone; 2,3-dihydroindolydione; refined indigo.
Indigo is yellow red crystal / orange red monoclinic prismatic crystal with bitter taste. It is insoluble in water (1.9 g / L, 20 ° C), but soluble in ethanol, ether and concentrated alkali solution. 201-204 ℃ sublimation (203 ～ 205 ℃)

                           

　The source of preparation of indigo: from indophenol or Indigo by oxidation. Indigo was first isolated by French chemist Auguste Laurent. In 1878, Adolf von Baer completed the total synthesis of indigo. In 1880, Bayer developed a method to synthesize indigo from o-nitrocinnamic acid. In 1883, Bayer applied for a patent for the synthesis of indigo from o-nitrobenzaldehyde. Since then, the method of synthesizing indigo with indigo as raw material has gradually replaced the method of extracting from plants and become the main source of indigo.
Use of indigo: indigo and its derivatives are used as raw materials for indigo and related dyes and some drugs. Because of its hepatotoxicity, indigo derivatives are no longer used in the pharmaceutical industry.
Usage and dosage of indigo: if urine is blue within 10 minutes after intravenous or intramuscular injection, it is normal.