1,1'-dithiobis[hexahydro-2H-azepin-2-one]

Hydrolysis

Description of key information

Experimental investigation, OECD 111, 50 °C, pH 4 and 7: hydrolytically stable; pH 9: half-life of 21.2 h, rate constant: 9.09E-6 s-1

Key value for chemical safety assessment

Half-life for hydrolysis:

21.2 h

at the temperature of:

50 °C

Additional information

The hydrolytic behaviour of the test substance as function of pH was carried out at 50 °C at pH 4, 7 and 9 in an experiment following the principles of OECD Guideline 111 (Neuland, 2012). Hydrolysis occurs, when a substance reacts with water. The kinetics is generally pseudo-first order at fixed pH and temperature. The substance concentration is determined as a function of time. High Performance Liquid Chromatography (HPLC) was the analytical method of choice. The test was performed under sterile conditions and in vessels protected from light. Samples were taken after 2h, 1d, 4d and 5d. The test substance was dissolved in the corresponding buffer solution for pH 4, 7 and 9, respectively. Aliquots of the stock solution were taken to obtain individual vials for every test point. Preparation was carried out under nitrogen as flushing gas to avoid oxygen. The calibration was verified daily at the level of 0.119 g/L by using a control calibration solution. The overall degradation of the test substance observed at 50 °C and pH 4 and 7 after 5 days was less than 10 %, concluding that under these conditions the test substance is stable and no half-life and hydrolysis rate were calculated. Furthermore, no sterility test was performed. In contrast to this, at pH 9, more than 90 % of test substance were degraded resulting in a half-life less than 24 hours. Therefore, the hydrolysis test at pH 9 was repeated with closer time intervals obtaining more test points up to > 90 % hydrolysis. This enables the calculation of the hydrolysis rate constant and half-life based on more analytical data. Samples were taken after 4h, 6h, 22h, 27h, 31h, 47h, 52h and 71h. The half-life was determined as 21.2 h with a rate constant of 9.09E-6 s-1 (0.00000909 s-1). A sterility test was conducted at the end of 90 % hydrolysis, whereby no microbes were found, concluding that biotic degradation can be ruled out. Caprolactam (Hexyhydro-2H-azepin-2-one, CAS 105-60-2) was determined as transformation product by Mass Spectrometry (MS). This is in compliance with the expected major hydrolysis product of the test substance.

Supporting information is available by the QSAR computer program HYDROWIN v1.00 (EPIWIN software) by US-EPA (Chemservice S.A., 2011).The program estimates the hydrolysis rate constants for specific organic classes and, furthermore, a chemical´s half-live under typical environmental conditions is also determined. In this case, AMIDES were detected as hydrolysable substance class. With the exception of a few halogenated acetamides, most amides hydrolyse to acids extremely slow with half-lives in centuries. Electronegative groups on carbon or nitrogen greatly accelerate base catalysed hydrolysis, but alkyl groups on nitrogen retard both acid and base catalysed processes. No neutral hydrolysis rate is evident. No GLP criteria are applicable for the usage of this tool, but due to the fact that it is a scientifically accepted calculation method the estimations performed are reliable with restrictions and can be used for the chemical safety assessment.