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Physical & Chemical properties

Water solubility

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Description of key information

Determination and significance of the water solubility values.

Key value for chemical safety assessment

Water solubility:
2 mg/L
at the temperature of:
22 °C

Additional information

Red SN is a co-precipitate of Basic Red 1 (BR1) and DowFax 2A1 as defined in section 1 of the IUCLID dossier with a ratio of 2 moles of BR1 for 1 mole of Dowfax 2A1.

The molecule Red SN has no specific absorbance and is therefore identified by the absorbance of both the BR1+ and the Dowfax 2A1 -. In normal conditions, there is no dissociation of the molecule Red SN, thus when both concentrations (BR1 and Dowfax) are measured as equivalent, it should correspond to the concentrations of the Red SN.


Several aqueous extractions have been prepared and analyzed thanks to photometry and then an HPLC has been performed to detect the different fractions (isomers, BR1+, Dowfax 2A1-).


All the 3 different assays reached the same conclusion: an excess of BR1+ from 1.9 to 3 mg/L and the possible presence of some Dowfax 2A1 traces.

Those findings imply that the hydrosolubility of Red SN is either not existing or existing but less than 0.1 mg/L. All the assays have been performed on the same batch. No dissociation of the molecule in water is expected. Although the manufacturing process is designed to be under stoichiometric conditions, the BR1+ excess is coming from an excess of BR1 during the manufacturing (and despite the purification steps). Assays on other dyes have shown that the excess of the starting material could be on either the cation or the anion. Therefore an excess of Dowfax cannot be excluded with another batch. This excess would be in the same range of values (1 to 5 mg/L max). Although it has been shown that the solubility of RED SN is less than 0.1 mg/L or not existing, a median value for the Red SN hydrosolubility of 2 mg/L has been used for the ecotoxicity and biodegradation assay, which corresponds to the excess of either the cation or the anion.