Tetrabutyltin

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

30 June and 21 August 2004

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

Samples from the test contents of a single flask (250 mL) was taken for extraction. The test material was extracted with two (2 x 10 mL) of dichloromethane, with the addition of sodium chloride to aid phase separation. Each extract was then filtered through a minimum quantitiy of anyhdrous sodium sulphate. The extracts were combined in a 20 mL volumetric flask and diluted to volume with dichloromethane prior to analysis.

Buffers:

pH: 4
- Type and final molarity of buffer: potassium hydrogen phthalate 0.05 mol/dm^3

pH: 7
- Type and final molarity of buffer: disodium hydrogen orthophosphate (anhydrous) (0.03 mol/dm^3); potassium dihydrogen orthophosphate (0.02 mol/dm^3) and sodium chloride (0.02 mol/dm^3)

pH: 9
- Type and final molarity of buffer: disodium tetraborate (0.01 mol/dm^3); sodium chloride (0.02 mol/dm^3)

A 1 % co-solvent of acetonitirle was used to aid solubility.

The buffer solutions were filtered through a 0.2 µm membrane filter to ensure that they were sterile. These solutions were also subjected to ultrasonication and degassing with nitrogen to minimise dissolved oxygen content.

Details on test conditions:

Sample solutions were prepraed in stoppered glass flasks at a nominal concentration of 4.0 x 10^-5 g/L in the three buffer solutions. A 1 % co-solvent of acetonitrile was used to aid solubility. the solutions were shielded from light whilst maintained at the test temperature. Solutions maintained at 50 °C for 7.5 hours and 168 hours for pH 4 and ph 7, respectively. Aliquots of solution were incubated in individual 250 mL volumetric flasks for each time point as an additional precaution against loss by volatilisation.

Duration:

2.4 h

pH:

4

Temp.:

50 °C

Initial conc. measured:

0.035 mg/L

Duration:

24 h

pH:

4

Temp.:

50 °C

Initial conc. measured:

0.035 mg/L

Duration:

120 h

pH:

7

Temp.:

50 °C

Initial conc. measured:

0.039 mg/L

Duration:

168 h

pH:

7

Temp.:

50 °C

Initial conc. measured:

0.039 mg/L

Duration:

120 h

pH:

9

Temp.:

50 °C

Initial conc. measured:

0.032 mg/L

Number of replicates:

2

Positive controls:

not specified

Negative controls:

not specified

Statistical methods:

Sample solution concentration:
The mean peak area of each standard was corrected to a nominal concentration of 0.5 mg/L and the mean value taken. The concentrations of the sample solutions (g/L) were calculated using the following equation:
Cspl = (Pspl/Pstd) x Cstd x D x 1/1000

Where:
Cspl = sample concentration (g/L)
Pspl = mean peak area of sample solution
Pstd = mean peak area of standard solution, corrected to nominal standard concentration
Cstd = nominal standard concentration (0.5 mg/L)
D = sample dilution factor (0.07 or 0.08)

Preliminary study:

The results of the initial test indicated that an additional preliminary test was required at pH 4, performed over a reduced period. The reduction in test material concentration after 24 hours indicated that a definitive test conducted at 50 °C was required to further investigate the test material. The reduction in test material concentration after 168 hours (pH 7) indicated that a definitive test conducted at 50 °C was required to further investigate the test material. Less than 10 % hydrolysis after 5 days at 50 °C (pH 9), equivalent to a half-life greater than 1 year at 25 °C.

Transformation products:

not specified

% Recovery:

74.7

pH:

4

Temp.:

50 °C

% Recovery:

79.2

pH:

7

Temp.:

50 °C

% Recovery:

74

pH:

9

Temp.:

50 °C

Key result

pH:

7

Temp.:

25 °C

DT50:

> 1 yr

Type:

not specified

Key result

pH:

9

Temp.:

25 °C

DT50:

> 1 yr

Type:

not specified

Details on results:

At pH 4, a decrease in concentration over time was consistently observed. However, the rate of decrease could not be accurately quantified, as the monitoring of the discrete changes in concentration appeared to exceed the limitations of the analytical method at this trace concentration. The nominal working concentration 4.0 x 10^-5 g/L was a constraint specified in the OECD method guideline, in that the initial concentration must remain below half water saturation. Based on the structural information supplied by the Sponsor and available literature references, no hydrolysis of the test material was anticipated. The literature references describes organotin compounds as chemically resistant to hydrolysis under normal conditions and that of the possible organic groups, butyl to tin bonds are most resistant to cleavage. Therefore, supported by analytical evidence of stability at pH 7 and pH 9, and literature references of stability, it is possible that the reduction in concentration at pH 4 originated not from hydrolysis but from adsorption onto the test vessel surfaces. The active sites on glass, free silanols, have a pKa of approximately 5 and therefore adsorption characteristics may be pH dependent.

Table 1: Summary or Results

pH	Result
7	>1 year
9	>1 year

 

Validity criteria fulfilled:

yes

Conclusions:

The estimated half-life at 25 °C at pH 7 and pH 9 is > 1 year. At pH 4, although a decrease in concentration over time was observed, significant sample to sample variance prevented accurate quantification of the rate. Based on literature reference to organotin compounds being chemically resistant to hydrolysis and the successful validation of the analytical procedure, the loss of test material from solution has been attributed to adsorption onto the test vessel surfaces, working at a negligible nominal concentration of 4.0 x 10^-5 g/L, not hydrolysis.

Executive summary:

Assessment of hydrolytic stability of tetrabutyltin was carried out using Method 111 of the OECD Guidelines for the Testing of Chemicals (12 May 1981). The results indicated the estimated half-life at 25 degrees C and pH 7 and 9 was >1 year.

Description of key information

The study is an OECD guideline study conducted to GLP standard. The estimated half-life at 25 ºC at pH 7 and pH 9 is > 1 year.

Additional information

The study is an OECD guideline study conducted to GLP standard. The estimated half-life at 25 ºC at pH 7 and pH 9 is > 1 year. At pH 4, although a decrease in concentration over time was observed, significant sample to sample variance prevented accurate quantification of the rate. Based on literature reference to organotin compounds being chemically resistant to hydrolysis and the successful validation of the analytical procedure, the loss of test material from solution has been attributed to adsorption onto the test vessel surfaces, working at a negligible nominal concentration of 4.0 x 10^-5 g/L, not hydrolysis.