Hexamethylene diisocyanate

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

weight of evidence

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)

Deviations:

no

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

Principles of method if other than guideline:

As the substance was expected to undergo fast hydrolysis in aqueous media the hydrolysis behaviour of the test item was investigated at 20 °C and 10 °C for pH 4, pH 7 and pH 9 up to a degradation of > 90%. As hydrolysis occurred very rapidly especially at 20°C, only 3 samplings were possible (e.g at 0, 4 and 9 minutes).

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

- pH of the blank buffer solution: checked at the beginning of the test; the pH of the hydrolysis solution was measured at each test point
- Suitability of the HPLC system: verified on every day of application
- Recovery and the repeatability of the analytical method: checked on every day of application

Buffers:

- Buffer pH 4: Citric acid/NaOH/NaCl (Fluka, Order no.: 33643)
- Buffer pH 7: KH2PO4/Na2HPO4 (Fluka, Order no.: 33646)
- Buffer pH 9: Na2B4O7/HCl (Fluka, order no.: 33648)

Details on test conditions:

TEST DESIGN (pH 4, 7 and 9):
I. Preparation of the hydrolysis test solutions:
- between 45.0 and 47.0 mg of the test item were accurately weighed and dissolved to 10 mL with acetonitrile (stock solution)
- 10 mL of the tempered buffer solution was first filled into a 20 mL brown glass vial
- 100 µL of the stock solution was added into the tempered buffer solution
- To determine the starting value (T0) 200 µL of the hydrolysis test solution was immediately transferred into a sample vial and diluted with 800 µL acetone; 1 µL of this sample solution was directly injected in the gas chromatographic system
- The hydrolysis test solution in buffer was closed and incubated under nitrogen as flushing gas at 10 °C (20 °C) in a heat regulator under dark
- Due to the fast hydrolysis of the test item individual vials for the next test points had to be prepared time-shifted
- For the next test point (5 min hydrolysis time) the sample preparation procedure was repeated: 10 mL of the tempered buffer solution was filled into a 20 mL brown glass vial and 100 µL of the stock solution was added into the tempered buffer solution
- After exactly 5 min hydrolysis time 200 µL of the hydrolysis solution was diluted with 800 µL acetone and analyzed directly by GC
- The test solutions for further test points (10 min, 15 min etc.) were prepared in the same way

II. Calculation of hydrolysis:
- Hydrolysis had been observed and calculated using the total peak area values of the test item corresponding to the concentrations of the respective main component PDI in the test solutions

III. pH determination:
- The determination was done with a pH-meter equipped with a calibrated single-rod glass electrode

IV. Solubility and test concentration:
- The test item was applied as aqueous buffer solutions (including 1 % acetonitrile) with a concentration of approx. 50 mg/L
- Clear solutions were obtained

Duration:

30 min

pH:

4

Temp.:

10

Initial conc. measured:

392.76 other: Peak area

Duration:

10 min

pH:

4

Temp.:

20

Initial conc. measured:

323.23 other: Peak area

Duration:

40 min

pH:

7

Temp.:

10

Initial conc. measured:

324.04 other: Peak area

Duration:

10 min

pH:

7

Temp.:

20

Initial conc. measured:

421.78 other: Peak area

Duration:

20 min

pH:

9

Temp.:

10

Initial conc. measured:

167.05 other: Peak area

Duration:

10 min

pH:

9

Temp.:

20

Initial conc. measured:

169.59 other: Peak area

Transformation products:

not measured

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

Due to the poor water solubility of the test item, a test concentration of approx. 50 mg/L (including 1 % acetonitrile as organic solvent additive) had to be applied for adequate dissolution. The low PDI concentration in the hydrolysis test solutions did not allow the identification of hydrolysis products with the applied analytical method which has to be used to follow the degradation of the parent substance. Polymeric or oligomeric ureas as potential hydrolysis products of PDI could not be determined as they are assumed to be insoluble in water.

% Recovery:

> 90

pH:

4

Temp.:

10 °C

Duration:

20 min

% Recovery:

> 90

pH:

4

Temp.:

20 °C

Duration:

10 min

% Recovery:

> 90

pH:

7

Temp.:

10 °C

Duration:

30 min

% Recovery:

> 90

pH:

7

Temp.:

20 °C

Duration:

10 min

% Recovery:

> 90

pH:

9

Temp.:

10 °C

Duration:

20 min

% Recovery:

> 90

pH:

9

Temp.:

20 °C

Duration:

10 min

pH:

4

Temp.:

20 °C

DT50:

< 5 min

Type:

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

Remarks on result:

other: estimated

pH:

4

Temp.:

10 °C

DT50:

< 5 min

Type:

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

Remarks on result:

other: estimated

pH:

7

Temp.:

20 °C

DT50:

< 5 min

Type:

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

Remarks on result:

other: estimated

pH:

7

Temp.:

10 °C

DT50:

< 5 min

Type:

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

Remarks on result:

other: estimated

pH:

9

Temp.:

20 °C

DT50:

< 5 min

Type:

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

Remarks on result:

other: estimated

pH:

9

Temp.:

10 °C

DT50:

< 5 min

Type:

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

Remarks on result:

other: estimated

Details on results:

Due to the observed rapid degradation of the test item within minutes, an exact determination of half-life time or hydrolysis rate was not possible. Therefore the halt-life times of PDI are estimated values based on the recoveries after 5 min hydrolysis time related to the initial value at 0 min, which was set to 100 %.

Solubility and test concentration:

- Based on a pre-test the test item was found to be soluble in aqueous buffer solutions (including 1 % acetonitrile) at a concentration of approx. 100 mg/L and clear solutions were obtained

- The test item was found to be soluble in this concentration which fulfills the requirements of OECD 111 and no further solubility test with organic solvent additives > 1% v/v was performed

Sterility test:

- Due to the rapid hydrolysis of up to > 90 % degradation within less than 30 minutes, biotic degradation could be excluded

- Therefore a sterility test at the end of the hydrolysis tests was not necessary and not conducted

Sensitivity:

Regarding exemplary chromatograms of the hydrolysis test solutions, the analytical method is sufficiently sensitive to quantify test item concentrations down to 10% or less of the initial concentration used in the hydrolysis experiment

Validity criteria fulfilled:

yes

Conclusions:

At pH 4, 7 and 9 the substance hydrolysed immediately in water at 20 °C. The estimated half-life time was lower than 5 minutes.

Executive summary:

The tests were performed based on OECD Guidelines for Testing of Chemicals, Section 1 – Physical-Chemical Properties, OECD 111, Council Regulation (EC) No 440/2008, Guideline Part C – Methods for the Determination of Ecotoxicity, C.7. “Abiotic Degradation: Hydrolysis as a Function of pH”. As the substance was expected to undergo fast hydrolysis in aqueous media the hydrolysis behaviour of the test item was investigated at 20 °C and 10 °C for pH 4, pH 7 and pH 9 up to a degradation of > 90%. Due to the observed rapid degradation of the test item within minutes, an exact determination of half-life time or hydrolysis rate was not possible. Therefore the halt-life times of PDI are estimated values based on the recoveries after 5 min hydrolysis time related to the initial value at 0 min, which was set to 100 %. Due to the poor water solubility of the test item, a test concentration of approx. 50 mg/L (including 1 % acetonitrile as organic solvent additive) had to be applied for adequate dissolution. The low PDI concentration in the hydrolysis test solutions did not allow the identification of hydrolysis products with the applied analytical method which has to be used to follow the degradation of the parent substance. Polymeric or oligomeric ureas as potential hydrolysis products of PDI could not be determined as they are assumed to be insoluble in water. The stability was monitored by GC analysis with FID-detection.

Description of key information

In a weight-of-evidence approach with one hydrolysis study performed according to OECD 111 with the analogeous substance Pentamethylene diisocyanate and a non-guideline study with hexamethylene diisocyanate, the half life at 10 and 20°C at pH4, 7 and 9 was <5 minutes. Hexamethylene diamine was found as a hydrolysis product as well as oligomeric and polymeric ureas.

Key value for chemical safety assessment

Half-life for hydrolysis:

5 min

at the temperature of:

20 °C

Additional information

Should read <5 minutes.