Primuline

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

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The primulines are considered derivatives of dehydrothiotoluidine (aminobenzenyltoluylmercaptan), which is obtained when para-toluidine is heated with sulphur 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 sulphur, then a base is formed, which gives primuline yellow upon sulphonation.^[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.

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.

References

1. ^ P. Jacobson (1889). "N/A". Ber. 22: 333.
   L. Gatterrnann, ibid. p. 1084
2. ^ A. G. Green (1888). "N/A". Journ. Soc. Chem. Ind. 1: 194.

• This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.