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Hydrolysis

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Description of key information

The hydrolysis of KMPS (triple salt) was investigated in one key study and two supporting studies. The key study is in accordance with the OECD Test Guidelines 111. However, as mentioned above organic materials present in water significantly influcene the rate of hydrolysis. Therefore, to realistically reflect environmental scenarios the hydrolysis rate in soil was used for chemical safety assessment (see IUCLID section 5.2.3).

Key value for chemical safety assessment

Half-life for hydrolysis:
0.02 d
at the temperature of:
12 °C

Additional information

KHSO5 can be degraded abiotically by hydrolysis to H2O2 and by disproportionation to O2. In both cases, potassium and hydrogensulfate ions are formed.

KHSO5 + H2O -> K+ + HSO4- + H2O2 (hydrolysis)

KHSO5 -> K+ + HSO4- + ½ O2 (disproportionation)

The degradation of KMPS triple salt in aqueous solution is pH and temperature dependant.

In the study, the degradation of KMPS triple salt was measured by determining the loss of active oxygen by iodometric titration. As the hydrolysis of KHSO5 does not result in a net loss in active oxygen (see equation above) but only in a transfer of the active oxygen from KHSO5 to water, which leads to the formation of hydrogen peroxide, only the degradation by disproportionation was determined in the above test.

The degradation of KMPS in aqueous solution is pH and temperature dependant. Degradation is accelerated with increasing temperature and increasing pH. While KMPS has a half-life of above 800 h (at 20°C) in a buffered solution of pH 4, the half-life at pH 7 is 145 hours and only 2.8 hours at pH 9. Degradation in seawater is considerably faster (DT50 = 5.5 hours, pH 8.0-8.2, 20°C) than in freshwater (DT50 = 215 hours, pH 7.8-8.2, 20°C).

The reason for the faster degradation of KMPS in seawater is the so-called Haber-Will-Statter Reaction. In this, the sodium chloride of the seawater is oxidised by KMPS so that chlorine is released.

HSO5- +2Cl- + 2H+ -> HSO4- + Cl2 +H2O

This endpoint is addressed for sake of completeness. It is no REACH requirement

The chlorine reacts with water to form hypochlorous acid:

Cl2 +H2O -> HOCl +HCl

Hypochlorous acid (HOCl) is only of transient nature, hypochlorous acid is extremely rapidly eliminated in the environment due to reaction with ammonia and organic material which act as reductants.