Sodium 2,4-diamino-5-(4-(2-sulfoxyethanesulfonyl)phenylazo)benzenesulfonate

Hydrolysis

Description of key information

Substance is not hydrolytically stable at pH 7, and 9 at environmental or use-conditions

Key value for chemical safety assessment

Half-life for hydrolysis:

78 h

at the temperature of:

25 °C

Additional information

The objective of this study was the determination of the abiotic degradation of the test substance Reactive Yellow 201, i.e. the determination of the hydrolysis rate as a function of the pH-value according to guideline 92/69/EEC. appendix, C7. Study performed in accordance with the Principles of Good Laboratory Practice (GLP).

 

A preliminary test at pH 4, 7, and 9 was carried out at 50°C.

At pH 4, less than 10% hydrolysis was observed after 5 days at 50°C. Hence the test substance was considered stable at acidic pH with an estimated half-life of greater than 1 year at 24°C.

At pH 7 and 50°C, only 55% test substance remained after 2.4 hours, and no substance was detected after 23 hours. Based on these results, a further test was carried out at pH 7 for 25°C, resulting in a half-life of 78 hours.

  

At pH 9 and 50°C, no substance was detected at the first measurement of 2.4 hours, hence the test substance was considered instable at basic pH. According to the guideline a half-life period of less than one day under environmental conditions (25°C) may be estimated.

In summary, it was concluded that the rate of hydrolysis increases with pH.

The rate constant and half-lifes are summrised in the following table:

pH	Rate constant (s^-1)	Half life at 25°C
4	-	Greater than 1 year
7	2.47 x 10^-6	78.0 hours
9	-	Less than 1 day