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Environmental fate & pathways

Hydrolysis

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Administrative data

Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)

Data source

Reference
Reference Type:
publication
Title:
Stability of chlorine dioxide in aqueous solution
Author:
Medir M and Giralt F
Year:
1982
Bibliographic source:
Water Res., 16, 1379-1382

Materials and methods

Principles of method if other than guideline:
Chlorine dioxide was prepared from 20 % sodium chlorite (commercial grade) solution by dropwise addition of 1N sulfuric acid. The generated chlorine dioxide was swept from the solution using nitrogen as carrier, passed through sodium chlorite solution to remove any chlorine formed and dissolved in double distilled water or in an aqueous solution of sodium chloride placed in the reaction vessel.
Reactions were carried out at 25°C in a jacketed pyrex glass reaction vessel of 500 mL protected from light and in the absence of gaseous phase. The pH was maintained constant at 9 by automatic addition of sodium hydroxide from a burette controlled by a pH-stat.
Experiments were carried out in sodium chloride concentrations of 0, 0.1, 0.4, 0.8 or 2.0 mol/L. Initial concentrations of chlorine dioxide were between 0.002-0.02 mol/L.
The initial concentration of chlorine dioxide was determined by acid-neutral iodometric titration with sodium thiosulfate. Chlorine dioxide consumption was determined by recording the addition of sodium hydroxide. Chlorine dioxide, chlorite and chlorate concentrations were determined by iodometric titration with sodium thiosulfate at different pH values. The chloride concentration was determined by titration with silver nitrate solution using both the Mohr method and the potentiometric method for detection of end point, after flushing the remaining chlorine dioxide out of the solution.
GLP compliance:
not specified

Test material

Constituent 1
Chemical structure
Reference substance name:
Chlorine dioxide
EC Number:
233-162-8
EC Name:
Chlorine dioxide
Cas Number:
10049-04-4
Molecular formula:
ClO2
IUPAC Name:
Chlorine dioxide generated from sodium chlorate and hydrogen peroxide in the presence of a strong acid
Details on test material:
- Analytical purity:

Not reported, however expected to be close to 100 % due to the method of production.
- Other:

Chlorine dioxide was prepared from 20 % sodium chlorite (commercial grade) solution by dropwise addition of 1N sulfuric acid. The generated chlorine dioxide was swept from the solution using nitrogen as carrier, passed through sodium chlorite solution to remove any chlorine formed and dissolved in double distilled water or in an aqueous solution of sodium chloride placed in the reaction vessel.
Radiolabelling:
no

Study design

Analytical monitoring:
yes
Details on test conditions:
Reactions were carried out at 25 °C in a jacketed pyrex glass reaction vessel of 500 mL protected from light and in the absence of gaseous phase. The pH was maintained constant at 9 by automatic addition of sodium hydroxide from a burette controlled by a pH-stat.
Experiments were carried out in sodium chloride concentrations of 0, 0.1, 0.4, 0.8 or 2.0 mol/L. Initial concentrations of chlorine dioxide were between 0.002-0.02 mol/L.
Duration of test
Duration:
400 min
pH:
9
Temp.:
25 °C
Initial conc. measured:
>= 0.002 - <= 0.02 mol/L
Number of replicates:
One test performed for each set of conditions.
Positive controls:
not specified
Negative controls:
not specified

Results and discussion

Preliminary study:
Not applicable
Transformation products:
yes
Identity of transformation productsopen allclose all
No.:
#1
Reference
Reference substance name:
Unnamed
IUPAC name:
Chlorate
Identifier:
common name
Identity:
Chlorate
No.:
#2
Reference
Reference substance name:
Unnamed
IUPAC name:
Chlorite
Identifier:
common name
Identity:
Chlorite
No.:
#3
Reference
Reference substance name:
Unnamed
IUPAC name:
Chloride
CAS number:
16887-00-6
Molecular formula:
Cl-
Molecular weight:
ca. 35.5
SMILES notation:
[Cl-]
No.:
#4
Reference
Reference substance name:
Unnamed
Inventory number:
InventoryMultipleMappingImpl [inventoryEntryValue=EC 231-956-9]
CAS number:
7782-44-7
Identity:
Oxygen
Molecular formula:
O2
Molecular weight:
31.999
SMILES notation:
O=O
InChl:
InChI=1/O2/c1-2
Details on hydrolysis and appearance of transformation product(s):
In the presence of sodium chloride, the degradation products were chlorite and chlorate in a 1:1 ratio.
In the absence of sodium chlorite, the degradation products were chlorate, chlorite, chloride and oxygen in a 5:3:1:0.75 ratio.
Dissipation DT50 of parent compound
Remarks on result:
not measured/tested
Details on results:
In aqueous solution at pH 9 there is a slow initial hydrolysis reaction followed by a more rapid one (Figure 1). The shape of the curve is indicative of an autocatalytic reaction. The length of the induction period for the second reaction is dependent of the concentration of the chlorine dioxide (at 0.02M the induction period is < 100 minutes, whereas at 0.003M the induction period is > 400 minutes). The degradation products are chlorate, chlorite, chloride and oxygen in a 5:3:1:0.75 ratio.
In the presence of sodium chloride there is a slow reaction of a few minutes duration (which is not appreciable in Figure 2) followed by a second faster reaction, which does not present an autocatalytic shape. The degradation products are chlorite and chlorate in a 1:1 ratio.

Applicant's summary and conclusion

Validity criteria fulfilled:
not applicable
Conclusions:
Aqueous solutions of chlorine dioxide are fairly stable at 25°C and pH 9 for an initial period of time before a fast decomposition takes place. The length of the initial stable period decreases with increasing chlorine dioxide concentration and in the presence of inert electrolytes. The reaction products are chlorate, chlorite, chloride and oxygen. Addition of sodium chloride reduces significantly the induction time, but slows down the second reaction and changes the product distribution to equal amounts of chlorite and chlorate.