Primuline is a dye containing the benzothiazole ring system. Primuline itself is also known as Direct yellow 7, Carnotine, or C.I. 49010.

Primuline

Names
Preferred IUPAC name Sodium 2′-(4-aminophenyl)-6-methyl[2,6′-bi-1,3-benzothiazole]-7-sulfonate
Other names Direct yellow 59
Identifiers
CAS Number	8064-60-6 N
3D model (JSmol)	Interactive image
ChEBI	CHEBI:90399 Y
ChemSpider	74524 Y
ECHA InfoCard	100.030.698
EC Number	233-781-3
PubChem CID	3769888
CompTox Dashboard (EPA)	DTXSID1065051
InChI InChI=1S/C21H15N3O3S3.Na/c1-11-2-8-16-18(19(11)30(25,26)27)29-21(24-16)13-5-9-15-17(10-13)28-20(23-15)12-3-6-14(22)7-4-12;/h2-10H,22H2,1H3,(H,25,26,27);/q;+1/p-1 Y Key: RSRNHSYYBLEMOI-UHFFFAOYSA-M Y InChI=1/C21H15N3O3S3.Na/c1-11-2-8-16-18(19(11)30(25,26)27)29-21(24-16)13-5-9-15-17(10-13)28-20(23-15)12-3-6-14(22)7-4-12;/h2-10H,22H2,1H3,(H,25,26,27);/q;+1/p-1 Key: RSRNHSYYBLEMOI-REWHXWOFAP
SMILES [Na+].[O-]S(=O)(=O)c1c(ccc2nc(sc12)c4ccc3nc(sc3c4)c5ccc(N)cc5)C
Properties
Chemical formula	C21H15N3O3S3 (free acid)
Molar mass	453.557 g/mol (free acid)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

The primulines are considered derivatives of dehydrothiotoluidine (aminobenzenyltoluylmercaptan), which is obtained when para-toluidine is heated with sulfur for eighteen hours at 180–190 °C and then for a further six hours at 200–220 °C^[1] Dehydrothiotoluidine is not itself a dye-stuff, but if the heating is carried out at a higher temperature in the presence of more sulfur, then a base is formed, which gives primuline yellow upon sulfonation.^[2]

Primuline yellow is a mixture of sodium salts and probably contains at least three thiazole rings in combination. It is a substantive cotton dye of rather fugitive shade, but can be diazotized on the fibre and then developed with other components, yielding a series of ingrain colors.^[3]

Primuline is usually available as a sodium salt. Primuline is fluorescent.

Thioflavin T is obtained by the methylation of dehydrothiotoluidine with methanol in the presence of hydrochloric acid. Thioflavin S results from the methylation of dehydrothiotoluidine with sulfonic acid. This sulfonic acid on oxidation with bleaching powder or with lead peroxide, in alkaline solution yields chloramine yellow, which dyes cotton a beautiful yellow.^[3]