3-((bis(diisopropylamino)phosphanyl)oxy)propanenitrile

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2017-01-30 to 2018-03-21

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Deviations:

yes

Remarks:

no pH adjustment, concentration range not in the recommended range, test design modified; see explanation below in "Principles of method if other than guideline".

Qualifier:

equivalent or similar to guideline

Guideline:

EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)

Qualifier:

equivalent or similar to guideline

Guideline:

EPA OPPTS 835.2120 (Hydrolysis of Parent and Degradates as a Function of pH at 25°C)

Principles of method if other than guideline:

- The results on the stability of the test item versus hydrolysis are supposed to be used as arguments for tests on further physico-chemical properties, especially the water solubility. The determination of hydrolysis is performed to find whether the water solubility of the test item can be determined or not. Therefore, the determination of hydrolysis in this study is limited to a modified pre-test (Tier 1). Usually the preliminary test is to be performed at 50 ± 0.5 °C and pH 4, pH 7 and pH 9. If less than 10% of hydrolysis is observed after 5 days (t0.5 (25°C) > 1 year), the test substance is considered hydrolytically stable and no additional testing is required. For the test item 2-Cyanoethyl-N,N,N’,N’-tetraisopropylphosphordiamidite the instability versus hydrolysis was known before the performance of the test. In deviation from the guideline a modified preliminary test was used. In this modified test a sample of the test item in acetonitrile-d3 was analysed repeatedly after addition of approx. 15 % (v/v) of water in increasing intervals starting after 13 min of hydrolysis time and going up to 172 min of hydrolysis time (for determination of rate constant) respectively up to 20 days of hydrolysis time (determination of hydrolysis products). For estimation of half-life time and hydrolysis rate constant the analytical method must be sufficiently precise and sensitive to determine the test item at concentrations of approx. 90% to 10% of the starting concentration which was possible with 31P-NMR at the given concentration level of the test item. For the determination of hydrolysis rates by 31P-NMR the concentration of the test item had to be chosen to be as high as possible to reach a maximum sensitivity of the NMR method. Although the starting concentration of the hydrolysis tests was much higher than half of the saturation concentration (in water) and the modifier content also was higher than described in the guidelines, the NMR experiment is regarded to give an accurate estimation of hydrolysis rate and half-life time with respect to the question of showing fast hydrolysis. Also, no special steps for cleaning and sterilization of glassware were performed, as because of the fast hydrolysis of the test item microbial degradation is not expected to be taking part.

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

- Sampling intervals for the parent/transformation products: a sample of the test item in acetonitrile-d3 was analysed repeatedly after addition of approx. 15 % (v/v) of water in increasing intervals starting after 13 min of hydrolysis time and going up to 172 min of hydrolysis time (for determination of rate constant) respectively up to 20 days of hydrolysis time (determination of hydrolysis products).
- Sampling intervals/times for sterility check: Due to the fast hydrolysis of the test item microbial degradation is not expected to be taking part. Therefore, no special steps for cleaning and sterilization of glassware were performed.
- Sample storage conditions before analysis: no storage

Estimation method (if used):

Because water is present in great excess compared to the chemical, this type of reaction is usually described as a pseudo-first order reaction in which the observed rate constant is given by the relationship:
[1] kobs = k[H2O]
This constant can be determined for one pH value and one temperature, T, using the expression:
[2] kobs = 1/t * ln(C0/Ct)
where:
t = time
C0, Ct = concentrations of the substance at times 0 and t.
The concentrations are expressed in grams per liter or moles per liter. The dimension of this constant kobs is (time)^-1. The half life period t1/2 is defined as the time required for reducing the concentration of the test item by 50%, that is:
[3] Ct=1/2 * C0
From the expressions [2] and [3] one can demonstrate that:
[4] t1/2=ln2/kobs

Assuming pseudo-first order kinetics as mentioned above the reaction rate k depends only on the pH value and the temperature. In order to determine the hydrolysis reaction, to acetonitrile-d3 solutions of the test item a defined amount of water was added and the solutions were incubated at a room temperature (approx. 22°C) without adjustment of pH. The hydrolysis results in the decrease of the test item concentration as a function of time. The logarithms of the concentrations are plotted against time and the slope of the resulting straight line (assuming first-order or pseudo-first order behavior) gives the rate constant from the formula.
[5] kobs = - slope

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: NMR tubes
- Sterilisation method: Due to the fast hydrolysis of the test item microbial degradation is not expected to be taking part. Therefore, no special steps for cleaning and sterilization of glassware were performed.
- Lighting: no
- Details on test procedure for unstable compounds: see below in “Any other information on materials andd methods”
- If no traps were used, is the test system closed/open: closed
- Is there any indication of the test material adsorbing to the walls of the test apparatus? No
TEST MEDIUM
- Volume used/treatment: 740 µL
- Kind and purity of water: distilled water
- Preparation of test medium: The test solutions were prepared by pipetting 40 µL of the test item into an NMR tube and addition of 0.6 mL of acetonitrile-d3. After performance of the initial measurement prior to hydrolysis, an exact amount of water (100 µL) was added to the sample.
- Renewal of test solution: no
OTHER TEST CONDITIONS
- Adjustment of pH: no

Duration:

20 d

Temp.:

22 °C

Initial conc. measured:

67 g/L

Remarks:

Due to the need for modified testing conditions (high content of organic modifier), the test was performed without adjustment of pH.

Positive controls:

no

Negative controls:

no

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

Details on hydrolysis and appearance of transformation product(s):

The structures of the found hydrolysis products are shown in Figure 2 below. The M+ signal of the unidentified hydrolysis product is 301 and therefore almost as high as the signal of the unhydrolysed test item. However, 31P-NMR proves that there is no unhydrolysed test item left after the reaction time of 360 hr. This signal is supposed to derive from any kind of dimer/oligomer that formed by intermolecular interaction of hydrolysis products.
Phosphonic acid which must form as the complementary hydrolysis product to diisopropylamine and 2-propenenitrile was not detectable by GC-MS. Anyhow the chemical shift of the main hydrolysis product in 31P-NMR is the chemical shift of phosphonic acid.
Summing up the known hydrolysis product, this means that approx. 65 % of the test item was converted to phosphonic acid, diisopropylamine and 2-propenenitrile. The rest is split into three more stable products, all containing at least one phosphorous atom. Two of these components are present at content levels around 13 %, the third at content levels of approx. 4 %. One of the compounds at a content level of 13 % could also be identified as propionic acid ester of phosphoric acid. This means that 78 % of the total hydrolysis products could be clearly identified while the rest stays unidentified.

Key result

Temp.:

22 °C

Hydrolysis rate constant:

0.024 min-1

DT50:

28.6 min

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: ue to the need for modified testing conditions (high content of organic modifier), the test was performed without adjustment of pH.

Validity criteria fulfilled:

yes

Conclusions:

The half-life time of 2-Cyanoethyl-N,N,N’,N’-tetraisopropylphosphordiamidite in water and acetonitrile was determined with 28.6 min and a hydrolysis rate constant kobs of 0.024/min.

Executive summary:

The abiotic degradation of the test item 2-Cyanoethyl-N,N,N’,N’-tetraisopropylphosphordiamidite was determined based on OECD-Guideline 111, European Commission Council Regulation (EC) No 440/2008, Annex, Part C, method C.7. and US EPA OCSPP 835.2120. Within this study a modified pre-test was performed to find out whether the test item is sufficiently stable in water to perform the determination of the water solubility.

Due to the known tendency of the test item to rapid hydrolysis the standard Tier 1 was not performed.

To be able to show the fast hydrolysis of the test item samples were prepared in NMR tubes and repeated measurements were performed at room temperature (approx. 22 °C). The test item was dissolved in acetonitrile-d3 and water was added to start hydrolysis. Due to the need for modified testing conditions (high content of organic modifier), the test was performed without adjustment of pH.

At room temperature (approx. 22 °C) the test item was found to be highly instable upon addition of water. Hydrolysis started immediately after addition of water to the dissolved test item. The analytical determination of the t = 0 min concentration was possible prior to addition of water. The first measurement of the test item after addition of water, that was achieved after approx. 13 min of hydrolysis time (incl. measuring time), showed hydrolysis at a level of approx. 17 %. The half-life time as well as the hydrolysis rate constant at room temperature (approx. 22 °C) could be estimated. For the given experimental set-up, the measured half-life time of the test item without pH adjustment was 28.6 min.

The free amine (diisopropylamine) as well as 2-propenenitril could be identified as the main hydrolysis products by GC-MS. Phosphonic acid must also have formed as a complementary hydrolysis product that was not detectable by GC-MS. 

 

Summary

 

Solvent: Acetonitrile + water

Half live time (22°C): 28.6 min

Hydrolysis rate constant kobs (22°C): 0.024/min

The results on the stability of the test item versus hydrolysis are supposed to be used as arguments for tests on further physico-chemical properties, especially the water solubility. The determination of hydrolysis is performed to find whether the water solubility of the test item can be determined or not.

Description of key information

The half live time of 2-Cyanoethyl-N,N,N’,N’-tetraisopropylphosphordiamidite in water and acetonitrile at 22 °C was determined with 28. 6 min and a hydrolysis rate constant k_obs of 0.024/min.

Key value for chemical safety assessment

Half-life for hydrolysis:

28.6 min

at the temperature of:

22 °C

Additional information

The results on the stability of the test item versus hydrolysis are supposed to be used as arguments for tests on further physico-chemical properties, especially the water solubility. The determination of hydrolysis is performed to find whether the water solubility of the test item can be determined or not. The results show that a test on water solubility of the test substance is technically not feasible.