Thioindigo is an organosulfur compound that is used to dye polyester fabric. A synthetic dye, thioindigo is related to the plant-derived dye indigo, replacing two NH groups with two sulfur atoms to create a shade of pink.

Thioindigo
Skeletal formula of thioindigo
Ball-and-stick model of the thioindigo molecule
Names
Preferred IUPAC name
[2(2′)E]-3H,3′H-[2,2′-Bi-1-benzothiophenylidene]-3,3′-dione
Other names
DyStar, C.I. Vat Red 41, C.I. 73 300
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.007.580 Edit this at Wikidata
UNII
  • InChI=1S/C16H8O2S2/c17-13-9-5-1-3-7-11(9)19-15(13)16-14(18)10-6-2-4-8-12(10)20-16/h1-8H/b16-15+ ☒N
    Key: JOUDBUYBGJYFFP-FOCLMDBBSA-N ☒N
  • InChI=1/C16H8O2S2/c17-13-9-5-1-3-7-11(9)19-15(13)16-14(18)10-6-2-4-8-12(10)20-16/h1-8H/b16-15+
    Key: JOUDBUYBGJYFFP-FOCLMDBBBL
  • O=C3c4ccccc4S/C3=C2/Sc1ccccc1C2=O
Properties
C16H8O2S2
Molar mass 296.36 g·mol−1
Appearance Red solid
Melting point 280 °C (536 °F; 553 K)
Insoluble
Solubility in ethanol, xylene Soluble[vague]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Thioindigo is generated by the alkylation of the sulfur in thiosalicylic acid with chloroacetic acid. The resulting thioether cyclizes to 2-hydroxythianaphthene, which is easily converted to thioindigo.[1] The related compound 4,7,4',7'-tetrachlorothioindigo, also a commercially important dye (Pigment Red 88), can be prepared by chlorination of thioindigo.

References

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  1. ^ Elmar Steingruber "Indigo and Indigo Colorants" in Ullmann's Encyclopedia of Industrial Chemistry, 2004, Wiley-VCH, Weinheim. doi:10.1002/14356007.a14_149.pub2