Registration Dossier
Registration Dossier
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EC number: 204-707-7 | CAS number: 124-64-1
Hydrolysis
Administrative data
Link to relevant study record(s)
Description of key information
Two hydrolysis studies of reliability 1 are available and have been defined as key studies. They have been performed with the parent salt of the registered substance; THPS.
The first study (O'Connor, 1992) has been performed in anaerobic conditions, as required by the test method when substances are
known to oxidise.
The second study (Yeomans, 2002) has been performed in non-anaerobic conditions and shows the effect of oxygen on the degradation
properties of THPS main ingredient.
In both test conditions, THPS main ingredient hydrolyses to THPO (Tris(hydroxymethyl) phosphine oxide,CAS No. 1067-12-5) and
formaldehyde (CASNo. 50-00-0).
Key value for chemical safety assessment
- Half-life for hydrolysis:
- 6.45 d
- at the temperature of:
- 12 °C
Additional information
Because of the salt nature of THPC, hazard properties of chloride salt could be predicted to be equivalent to hazard properties of the sulphate salt (THPS). In the case of hydrolysis, THPS and THPC follow the same degradation pathway via THP and THPO formation. The read across with THPS is then considered as relevant.
In anaerobic conditions the degradation pathway is believed to proceed via the dissociation product THP (Tris (hydroxymethyl) phosphine, CAS No. 2767-80-8). The formation of THP is favoured as the pH is raised, and the hydrolysis rate constant increases with increasing pH.
In anaerobic conditions, the half lives measured at 25°C were:
131 days at pH=5
72 days at pH=7
7 days at pH= 9
In non-anaerobic conditions, THPS reacts with dissolved oxygen to form THPO and formaldehyde. The degradation rate constants are higher in presence of oxygen, and increase with decreasing pH.
In non-anaerobic conditions, the half lives measured at 20°C were:
1.5 d at pH=5
and 3.4 d at pH=9,
which gives values calculated at 12°C:
2.8 d at pH=5
and 6.45 d at pH=9
THPC is then expected to behave in a similar way:
- in anaerobic conditions, the hydrolysis (and THP formation) is favoured with increasing pH (with half lives in a range of a week at pH9)
- in aerobic conditions, the hydrolysis is faster in acidic conditions (with a half life about 3 days at pH 5)
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