2,4,6-triisopropyl-m-phenylene diisocyanate

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

04 APR 2019 - 01 APR 2020

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)

Version / remarks:

EC No 440/2008

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: internal standard operation procedures and methods

Version / remarks:

SOP 00192 version 3 – Currenta-internal standard operation procedure based on the guidelines mentioned above.
SOP 00178 version 3 – Determination of the pH-value of the hydrolysis test solutions.
SOP 00074 version 3 – Determination of sterility by a plate count test (according to Ph.Eur.6)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

At each test point 500 μL of the hydrolysis test solution was mixed and diluted with 500 μL derivatization agent (solution of dibutylamine in acetonitrile).

The concentration of the test item and the hydrolysis product in the sample solutions was determined by HPLC-MS/MS at defined time intervals. As the test item was expected to undergo very fast hydrolysis in aqueous media, the test points were set within short time intervals (each after approx. 12 – 20 s). At each test point individual samples were prepared at which the reactive NCO functions of the test item were derivatized with dibutylamine.

Number of replicates:

2

Preliminary study:

The test item was found to be soluble in demineralized water including 1 % acetonitrile as organic solvent additive with a solubility of at least 80 μg/L.

Transformation products:

yes

No.:

#1

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

Q1 Mass [Da]: 235.0
Q3 Mass [Da]: 218.0

Q1 Mass (235.0 Da) corresponds to [M+H]+

Remarks on result:

other: please refer to 'Any other information on results incl. tables'

Temp.:

20 °C

Hydrolysis rate constant:

0.019 s-1

DT50:

37 s

Type:

not specified

Remarks on result:

other: pH = 5-6

Remarks:

pH-values could not be precisely determined with the pH meter due to lack of ions in the hydrolysis test solutions. For this reason pH indicator strips were used

Results of Hydrolysis

Hydrolysis of the test item at 20 °C: see table below (Overall hydrolysis at 20 °C)

Test item  first determination			Test item  second determination
Hydrolysis time [s]	Conc. [µg/L]	Recovery of the initial concentration [%]	Hydrolysis time [s]	Conc. [µg/L]	Recovery of the initial concentration [%]
0	40	--	0	40	--
12	28.26	70.6	9	27.2	68.0
28	20.82	52.1	23	22.31	55.8
41	15.81	39.5	33	18.42	46.1
60	11.53	28.8	53	12.43	31.1
75	8.55	21.4	69	9.90	24.7
93	6.05	15.1	89	6.74	16.8
188	1.02	2.5	16	5.82	14.6
--	--	--	128	3.41	8.5
--	--	--	148	2.21	5.5
pH value*	5 -6		pH value*	5 -6
Half life time at 20 °C	t(1/2) = 36.2 seconds    t(1/2)= 0.010 hours		Half life time at 20 °C	t(1/2)= 38.0 seconds t(1/2)= 0.011 hours
Hydrolysis rate constant	k = 0.0192 s^-1		Hydrolysis rate constant	k = 0.0182 s^-1
Remark (*): pH-values could not be precisely determined with the pH meter due to lack of ions in the hydrolysis test solutions. For this reason pH indicator strips were used.

The concentration of the test item after approx. 150 min is determined to be < 10 % of the initial value. The test item is therefore considered to be hydrolytically unstable in demineralized water at 20 °C.

According to OECD 111 Guideline a sterility test was conducted at the end of > 90 % hydrolysis. No microbes (colonies) were found. Therefore biotic degradation can be excluded.

Half-life time: 37 s (mean of two determinations)

Hydrolysis rate constant: k = 0.0187 s^-1 (mean of two determinations)

Monitoring of the hydrolysis produckt TRIDA: see table below (Concentration of TRIDA in hydrolysis test solutions)

TRIDA  first determination		TRIDA  second determination
Hydrolysis time [s]	Conc. [µg/L]	Hydrolysis time [s]	Conc. [µg/L]
28	< LOQ	33	< LOQ
41	< LOQ	52	2.03
60	2.86	69	4.23
75	2.65	89	4.23
93	3.82	106	4.09
188	8.42	128	4.50
207	8.88	148	5.79
238	10.50	166	6.73
279	11.86	200	9.02
336	12.76	285	12.96
395	16.58	331	12.75
466	16.83	393	15.44
528	17.83	511	18.85
644	21.61	637	18.83
775	21.84	761	21.91
900	22.75	905	22.91

After approx. 900 s (15 min) hydrolysis time the concentration of the major hydrolysis product TRIDA in the test solutions is determined to be about 23 μg/L.

QUALITY CRITERIA

Recovery

The recovery of the analytical method was checked during the hydrolysis study by analyzing an independent control solution for verification of the calibration containing the test item and TRIDA at a concentration of 10 μg/L. The control solution was analyzed on the days of application directly before and also immediately after analyzing the test solutions: see table below (Recovery of the test item and hydrolysis product TRIDA)

Date of analysis of control solution	Theoretical concentration [µg/L]	Measured concentration [µg/L]	Recovery of the theoretical concentration [%]
	Test item / TRIDA	Test item / TRIDA	Test item / TRIDA
2019 -04 -05	9.995 / 9.992	11.059 / 10.391	110.6 / 104.0
		11.023 / 10.745	110.3 / 107.5
		11.314 / 10.577	113.2 / 105.9
		11.203 / 10.367	112.1 / 103.7
2019 -04 -06		11.034 / 10.570	110.4 / 105.8
		11.072 / 11.671	110.8 / 116.8
		11.138 / 10.248	111.4 / 102.6
		10.889 / 10.872	108.9 / 108.8
Mean value			111.0 / 106.9
Relative standard deviation			1.2 / 4.2

Results of the solutions for verification of the calibration show stability of the chromatographic system. Recoveries of the test item TRIDI and the hydrolysis product TRIDA in the range from approx. 103 % to 117 % and relative standard deviations of 1.2 % and 4.2 % indicate a satisfactory repeatability and precision of the method applied to quantify the test item concentrations over the test duration.

Sensitivity

Regarding the chromatogram of the concentration level of 2 μg/L used for calibration the analytical method is sufficiently sensitive to quantify test item concentrations at least down to 10 % or less of the initial concentration used in the hydrolysis experiment.

Validity criteria fulfilled:

yes

Conclusions:

Half-life time: 37 s (mean of two determinations)
Hydrolysis rate constant: k = 0.0187 s-1 (mean of two determinations)

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” in a GLP study.

As the test item was expected to undergo fast hydrolysis in aqueous media the hydrolysis behavior was investigated at 20 °C in demineralized water up to a degradation of > 90 %. The stability was monitored by HPLC analysis with MS/MS-detection.

The concentration of the test item in the hydrolysis test solutions was determined by HPLC-MS/MS at defined time intervals after derivatization of the NCO function with dibutylamine.

Additionally, the formation of the expected major hydrolysis product 1,3,5-triisopropyl-2,4-diaminobenzene (TRIDA), M = 234 g/mol, CAS no.: 6318-09-8 was monitored over time.

Analytical result:

For the test item TRIDI abiotic degradation > 90 % was observed within 3 min at 20 °C in demineralized water.

The concentration of the test item after approx. 3 min is determined to be < 5 % of the initial value.

The test item is therefore considered to be hydrolytically unstable in demineralized water at 20 °C.

According to OECD 111 Guideline a sterility test was conducted at the end of > 90 % hydrolysis. No microbes (colonies) were found. Therefore biotic degradation can be excluded.

The following half-life time and hydrolysis rate were calculated for 20 °C:

Half-life time: 37 seconds (mean of two determinations)

Hydrolysis rate constant: k = 0.0187 s^-1 (mean of two determinations)

Monitoring and quantification of hydrolysis products:

1,3,5-triisopropyl-2,4-diaminobenzene (TRIDA), CAS no.: 6318-09-8, was expected as major hydrolysis product and monitored over time in the hydrolysis test solutions. After approx. 15 min hydrolysis time the concentration of TRIDA in the test solutions was determined to be about 23 μg/L.

As the parent substance was applied at a concentration of 40 μg/L in the test solutions, TRIDA can certainly be assessed as most predominant hydrolysis product. Polymeric or oligomeric ureas as potential minor hydrolysis products could not be determined as they are assumed to be insoluble in water.

Description of key information

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” in a GLP study.

As the test item was expected to undergo fast hydrolysis in aqueous media the hydrolysis behavior was investigated at 20 °C in demineralized water up to a degradation of > 90 %. The stability was monitored by HPLC analysis with MS/MS-detection.

The concentration of the test item in the hydrolysis test solutions was determined by HPLC-MS/MS at defined time intervals after derivatization of the NCO function with dibutylamine.

Additionally, the formation of the expected major hydrolysis product 1,3,5-triisopropyl-2,4-diaminobenzene (TRIDA), M = 234 g/mol, CAS no.: 6318-09 -8 was monitored over time.

Analytical result:

For the test item TRIDI abiotic degradation > 90 % was observed within 3 min at 20 °C in demineralized water.

The concentration of the test item after approx. 3 min is determined to be < 5 % of the initial value.

The test item is therefore considered to be hydrolytically unstable in demineralized water at 20 °C.

According to OECD 111 Guideline a sterility test was conducted at the end of > 90 % hydrolysis. No microbes (colonies) were found. Therefore biotic degradation can be excluded.

The following half-life time and hydrolysis rate were calculated for 20 °C:

Half-life time: 37 seconds (mean of two determinations)

Hydrolysis rate constant: k = 0.0187 s^-1(mean of two determinations)

Monitoring and quantification of hydrolysis products:

1,3,5-triisopropyl-2,4-diaminobenzene (TRIDA), CAS no.: 6318-09-8, was expected as major hydrolysis product and monitored over time in the hydrolysis test solutions. After approx. 15 min hydrolysis time the concentration of TRIDA in the test solutions was determined to be about 23 μg/L.

As the parent substance was applied at a concentration of 40 μg/L in the test solutions, TRIDA can certainly be assessed as most predominant hydrolysis product. Polymeric or oligomeric ureas as potential minor hydrolysis products could not be determined as they are assumed to be insoluble in water.

Key value for chemical safety assessment

Half-life for hydrolysis:

37 s

at the temperature of:

20 °C

Additional information

General condiderations about hydrolysis behaviour of isocyanates which are in line with the experimental results of the above mentioned key-study:

Information on hydrolysis potential of the test substance wer derived using the computer program HYDROWIN v2.00 (EPIWIN software) by US-EPA (2012).The program estimates the hydrolysis rate constants for specific organic classes and, furthermore, a chemical´s half-life under typical environmental conditions is also determined. Only esters, carbamates, epoxides, halomethanes (containing 1-3 halogens), specific alkyl halides and phosphorous esters can be estimated, since these are specific organic classes, which are able to undergo hydrolysis. When present, various hydrolysable compound-types will be identified. In the query structureISOCYANATES (-N=C=O) were detected as hydrolysable substance class. Even at low pHs, the hydrolysis half-life will be less than 10 minutes at 25 °C. Isocyanates hydrolyse readily in water to yield carbamic acid, which will decarboxylates to yield CO₂ and an amine. The amine reacts further with other isocyanates to produce disubstituted urea. Electron-withdrawing substituents influence the hydrolysis rate, as well as sterical hindrances. According to Ullmann´s Encyclopedia the aliphatic isocyanate rates are as followed: primary > secondary > tertiary. Methyl isocyanate possesses a hydrolyses rate of 9 minutes, phenyl isocyanate of 55 seconds (in water/dioxane solution) at 25 °C (HSDB, 2007).