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Hydrolysis

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Description of key information

Butyl 3,5-bis(1,1-dimethylethyl)-4-hydroxybenzenepropanoate (CAS 52449-44-2): stable against hydrolysis at pH 4 and pH 7 at 25 °C (half-life greater than 1 year). At pH 9 the half-life at 25 °C was estimated as 28.9 days with a rate constant of 0.000000278 s-1. 
Benzenepropanoic acid, 3,5 -bis(1,1 -dimethylethyl)-4 -hydroxy-2 -ethylhexylester (CAS 144429-84-5): Stable against hydrolysis at pH 4 and pH 7 at 25 °C (half-life greater than 1 year). At pH 9 the half-life at 25 °C was estimated as 15.2 days with a rate constant of 0.000000528 s-1.
According to the available read-across data it can be assumed that Benzenepropanoic acid, 3,5 -bis(1,1 -dimethylethyl)-4 -hydroxy-,C7 -9 branched alkyl esters (CAS 125643-61-0) is also not persistent in air.

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Additional information

No data are available regarding hydrolysis of Benzenepropanoic acid, 3,5 -bis(1,1 -dimethylethyl)-4 -hydroxy-,C7 -9 branched alkyl esters (CAS 125643 -61 -0). However, for two read-across substances experimental results are available and described as followed:

For the read-across substance Butyl 3,5-bis(1,1-dimethylethyl)-4-hydroxybenzenepropanoate (CAS 52449-44-2) the determination of abiotic degradation for the test subsance was carried out using Method C7 of Commission Directive 92/69/EEC (O´Connor, 2000). Three buffer solutions were prepared for pH4, 7 and 9, respectively. Sample solutions were prepared in stoppered glass flasks at a nominal concentration of 4.0 x 10E-5 g/L in the three buffer solutions using an acetonitrile co-solvent of less than 1% total volume. For the first test, the sample solutions were maintained at 50 +/- 0.5 °C for a period of 264 hours, 336.75 hours and 28 hours respectively for the three pH's. The results of this test showed that it was necessary to undertake further testing at pH 9, with a solution being maintained at 40 +/- 0.5 °C for a period of 44.5 hours. The solutions were analysed by High Performance Liquid Chromatography (HPLC) using acetonitrile:water (95:5 v/v) as mobile phase and a column temperature of 40 °C. The kinetics of the study have been determined to be consistent with that of a pseudofirst order reaction as the graphs of log10 concentration versus time are straight lines at pH 9. It has been observed that the rate of hydrolysis increases with an increase in pH. Prior to initiation of testing, the extraction procedure used was validated in triplicate

for each pH at a nominal concentration of 4.0 x 10E-5 g/L. The mean recovery was 67.6 %, 65.3 % and 64.5 % at pH 4, 7 and 9, respectively.

The initial pH 4 concentration has been excluded from calculations since the percentage recovery, when calculated from the theoretical as weighed value, was significantly higher than that observed during method validation. Therefore, since over a period of greater than 120 hours (96 hours to 264 hours) negligible hydrolysis was observed, it has been concluded that less than 10 % hydrolysis occurred during 5 days at 50 °C. This is equivalent to a half life of greater than 1 year at 25 °C. The minor fluctuations in test material concentration over time are considered insignificant as they are within the expected variation of the analytical method at the low concentrations employed in the study.

At pH 7, although hydrolysis was observed, it was not possible to accurately quantify the rate kinectics due to the slow rate of hydrolysis even at elevated temperatures. This is since any significant trend in test material concentration versus time was masked by analytical variance due to the extremely low initial concentration required to satisfy the guideline requirements. Therefore, it was not experimentally possible to determine the pH 7 hydrolysis reaction kinetics for the test substance. As an alternative the pH 7 hydrolytic half life has been estimated as greater than 1 year using the software HYDROWIN, version 1.67, Syracuse Research Corporation Inc., William Meylan, 1994 - 1999. At pH 9, a rate constant of 2.78 x 10E-7 s-1 (0.000000278 s-1) and an estimated half-life of 28.9 days at 25 °C was reported.

An experimental result is also available for the second read-across possibility Benzenepropanoic acid, 3,5 -bis(1,1 -dimethylethyl)-4 -hydroxy-2 -ethylhexylester (CAS 144429 -84 -5). The hydrolysis potential of this substance was determined according to OECD Guideline 111 (Woolley and Mullee, 2007). Three buffer solutions were prepared for pH4, 7 and 9, respectively. Sample solutions were prepared in stoppered glass flasks at a nominal concentration of 0.00005 g/L in the three buffer solutions. A 1% co-solvent of acetonitrile was used to aid solubility. In the first approach, the sample solutions were maintained at 50 +/- 0.5 °C for a period of 144 hours for pH 4,120 hours for pH 7 and 24 hours for pH 9. Furthermore, it was necessary to undertake testing at pH 9, with solutions being maintained at temperatures of 30.4 and 50 +/- 0.5 °C. The concentration of the sample solution was determined by high performance liquid chromatography (HPLC). The kinetics of the study have been determined to be consistent with that of a pseudo-first order reaction as the graphs of logio concentration versus time are straight lines. It has been observed that the rate of hydrolysis increases with an increase in pH. Testing was carried out at approximately half the water solubility limit value. It was possible that this exceeded the true water solubility. However, it was considered appropriate to attempt the test since it was anticipated that the test material would hydrolyse (ester). This would probably explain the analytical variation evident in the results, especially at pH 4, since the test material is an acid and would be even less soluble at this pH. No rate constant could be determined at pH 4 and 7, whereby the half-live at 25 °C will be greater than 1 year. At pH 9 a rate constant of 0.000000528 s-1 (5.28 x 10E-7 s-1) is reported as well as a half-life of 15.2 days at 25 °C.

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