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EC number: 205-087-0
CAS number: 133-06-2
The hydrolysis preliminary test was performed with THPI at 50.0 ± 0.1°C at each of pH 4.0, pH 7.0 and pH 9.0 in duplicate. The test solutions of THPI were thermostated to 50.0°C and analysed in time intervals.
The concentrations of THPI found in the test solutions after Incubation times of 2.4 hours, 24 hours and 5 days are given in the following table. The tabulated values represent rounded results which were obtained by calculation using the exact raw data (please look at attached background material).
The hydrolysis of the
test item was performed at 50.0°C ± 0.1 °C at each of pH 4.0, pH 7.0 and
THPI was found to be
stable at pH 4.0 and 50°C. Therefore no further testing was performed at
THPI was not stable at
pH 7.0 and at pH 9.0, further testing was performed at elevated
temperatures in order to calculate the rate constant (k25) and the
half-life time of the hydrolysis at pH 7.0, pH 9.0 at 25°C.
Several unknown degradation products were found by HPLC analysis.
Decomposition products depend on pH (refer to tables attched).
The hydrolysis of
[trichloromethyl-14C]captan has been examined at 25°C in
aqueous solutions buffered at pH 5, 7, and 9. The studies were carried
out in the dark, under sterile conditions, with concentrations of
labeled captan at 2.15 mg/L. At 25°C, captan degraded rapidly in water
with a half-life of 18.8 hours at pH 5, 4.9 hours at pH 7, and 8.3
minutes at pH 9.
At pH 5, the major
hydrolytic degradate was identified as CO2.
At pH 7 and pH 9, CO2was
also formed in addition to two other degradates. Available evidence
suggested that the latter, too unstable to be characterized fully, are
presumably sodium thiocarbonate and sodium
S-(tetrahydrophthalimido)thiocarbonate, both of which rapidly degraded
to produce CO2 -recovery, obtained from the analysis of
radioactivity, was nearly quantitative; 97% at pH 5, 92% at pH 7, and
103% at pH 9.
In the present study,
characterizations were attempted only for those products containing the
trichloromethyl moiety leading to carbon dioxide and sodium carbonate as
Addtionally it is well known
from studies on captan as active substance in plant protection products
that further transformation products are THPI and THPAM.
Captan is hydrolysing with half-life times from 18.8 hours at pH 5 to 8.3 minutes at pH 9. The major hydrolytic degradation product was found to be CO2 and THPI.
THPI is stable at pH 4.0. Its half-life time is longer than one year at 25 °C.THPI at pH 7.0 has a half-life time of 3658 hours (152 days) at 25 °C.THPI at pH 9.0 has a half-life time of 76 hours (3 days) at 25 °C.
Hydrolysis of captan is in a range from 18.8 hours in acidic to 8.3
minutes in alkaline water. At pH 7 a half-life time of 4.9 hours was
determined. Fast hydrolysis and low solubility of 3.8 mg/L has to be
considered for formulation uses and subsequent cleaning processes
Captan exhibited very rapid first order hydrolysis at all pH values in
sterile water, the rate of degradation increasing with pH. The first
order half-lives were in the range 11 to 18.8 hours at pH 5, 2.6 to 4.9
hours at pH 7 and 3.6 to 8.3 minutes at pH 9 at 25°C in various
experiments. Carbon dioxide was evolved at acidic and neutral pH´s, and
dissolved in solution as carbonate at alkaline pH´s. At neutral and
alkaline pH, three unidentified degradates were observed, containing
radiolabel derived from the trichloromethyl [14C] position, two of which
did not contain the tetrahydrophthalate moiety.
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