Pentasodium bis{7-[4-(1-butyl-5-cyano-1,2-dihydro-2-hydroxy-4-methyl-6-oxo-3-pyridylazo)phenylsulfonylamino]-5'-nitro-3,3'-disulfonatonaphthalene-2-azobenzene-1,2'-diolato} chromate (III)

Hydrolysis

Description of key information

The half-time  at 25 °C were found to be:

- at pH 4 t½ (25 °C) > 1 year

- at pH 7.0 t½ (25 °C) = 1.8 years

- at pH 9.0 t½(25 °C) = 4.8 years.

Key value for chemical safety assessment

Half-life for hydrolysis:

1.8 yr

at the temperature of:

25 °C

Additional information

Hydrolysis as a function of pH was determined according to OECD Guideline No. 111 (1981) and the Method C.7 of the EEC Directive 92/69.The hydrolysis of the test substance was performed at 50 °C ± 0.1 °C at each of pH 4.0, pH 7.0, and pH 9.0.

The results of pH 4.0 showed no significant degradation of test item. The percentage of hydrolysis at pH 4.0 was found to be less than 10 % after 5 days incubation at 50 °C ± 0.1 °C. Therefore the substance was considered to be hydrolytically stable at pH 4.0 and according to the guidelines no further testing was performed pH 4.0.

The results at pH 7.0 and pH 9.0 showed that the substance is not stable at this pH range. The percentage of hydrolysis at pH 7.0 and pH 9.0 were found to be more than 10 % after 5 days at 50 °C. Therefore, according to the guidelines advanced testing was performed to determine the rate constant (k25) of test item reaction at pH 7.0 and pH 9.0.