Dioctyltin dilaurate

Hydrolysis

Description of key information

The substance will immediately hydrolyse (< 4.5 hours) to dioctyltin oxide (insoluble) and lauric acid in the presence of water.

Key value for chemical safety assessment

Half-life for hydrolysis:

4.5 h

at the temperature of:

20 °C

Additional information

In the key study (Lange, 2012a), hydrolysis as a function of pH was investigated in a GLP study which was conducted in accordance with standardised guidelines OECD 111 and EU Method C.7. Testing was performed on the registration substance, dioctyltin laurate, at pH 4, 7 and 9 at 20, 30 and 50 °C. Dioctyltin laurate was applied at 400 mg/L (v/v) in test systems. For pH 4, 7 and 9, samples were taken at test initiation and at 8 spaced points. Buffer solutions were analysed at test initiation and at test termination and there was no analytical interference with dioctyltin laurate.

At the start of the study (0 h sampling) very high concentrations of the transformation products were observed. Analysis of 0 h samplings were performed within 4.5 hours after application. For the C12 carboxylic acid, transformation rates significantly above 50 % of the applied dioctyltin laurate were calculated indicating a rapid aqueous transformation. On further sampling intervals, a steady state or even a reduction of the carboxylic acid concentrations were observed. In all samples a white precipitate was observed and removed before analysis. Therefore, it could be concluded that dioctyltin laurate will immediately be hydrolysed in the presence of water, therefore no reaction rate constants or half life values could be calculated. Based on the results obtained it could be concluded that the half life of dioctyltin laurate is below 4.5 hours for the main compound (C12 carboxylic acid homologue) and slightly above for the longer chain homologues.

 

Two studies are available on the structural analogue of the registration substance, of di-n-octyltin oxide den 2,4-pentanedione.

In the first study (Lange, 2012b), hydrolysis as a function of pH was investigated in a GLP study which was conducted in accordance with the standardised guidelines OECD 111 and EU Method C.7. Testing was performed at pH 4, 7 and 9 at 20 ± 0.5 °C. Di-n-octyltin oxide den 2,4-pentanedione was applied at 0.1 % (v/v) in test systems. Immediately after application, a reaction of di-n-octyltin oxide den 2,4-pentanedione with the buffer was visually observed by formation of a white amorphous precipitate. Samples were taken at test initiation and every 10 minutes thereafter until a plateau phase was reached.

As a direct analysis of the test material from aqueous solution was not possible, the known transformation product 2,4-pentadione was analysed via HPLC-DAD. Quantification was performed against an external standard. The analytical method was validated with satisfactory results in regard to linearity, repeatability of injection, accuracy and specificity. Analyses indicated a plateau phase for the 2,4-pentadione content for all tested conditions after at least 10 minutes. A mass balance, based on analysed 2,4-pentadione could not be established. It was assumed that the reduced, but reproducible, 2,4-pentadione content was caused by adsorption to the employed filter material, necessary for the elimination of the precipitate. This was confirmed by representative IR measurements performed in a separate study.

Reaction rate constants and half lives for all tested conditions could not be assessed, as the hydrolysis reaction was completed within the first two analyses. Taking visual observation of the immediate precipitation into account, it could be assumed that the hydrolytical half life is significantly lower than the time needed for the first sampling (10 minutes).

Based on chemical deliberation, the transformation product (precipitate) was assumed to be n-dioctyl oxide. The identity was confirmed by X-ray spectroscopy in a separate study.

 

In the second study (Hansen, 2011d) the hydrolysis products of di-n-octyltin oxide den 2,4-pentanedione were investigated using IR and NMR spectroscopy. During the study 10 g of test material was added to 90 g of distillated water and stirred for 48 hours at room temperature. On the border of the beaker and on the top of the water phase a white substance was formed. This substance was filtered out and washed several times with distilled water and later with n-hexane. After drying the substance for 24 hours at 50 °C in a vacuum it was analysed by IR and 119Sn-NMR spectroscopy.

The IR spectrum of the hydrolysis product of the test material was analogous to that of dioctyltin oxide thereby confirming it as a hydrolysis product. The resolution of the NMR spectra was found to be insufficient.

 

Further information is available in the form of a study on the hydrolysis of dioctyltin oxide (Yoder, 2003). The aim of the study was to use electrospray ionisation mass spectrometry (ESI/MS) to determine whether dioctyltin compounds in water behave like dibutyltin compounds and form oxides relatively quickly. Although dioctyltin oxide was of interest in the study, difficulties arose preparing samples for analysis and the solubility of dioctyltin oxide itself, as no detectable amount could be dissolved in any solvent. Furthermore, it was not possible to make standards for dioctyltin oxide. Surrogate standards for other dioctyltin species were not possible as they gave multiple species when analysed and the relative ratio of the species changed with concentration. It could also not be determined whether all the species had the same ionisation effect as the oxide. No conclusion concerning the hydrolysis of dioctyltin oxide could be determined.