3,4-dichlorophenyl isocyanate

Hydrolysis

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

hydrolysis

Type of information:

other: expert statement based on an experimental study conducted with the closely related 4-chlorophenyl isocyanate (CAS 104-12-1)

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: expert statement based on common reactivity of phenyl isocyanates and

Justification for type of information:

It is commonly known that phenyl isocyanates are prone to hydrolysis. The isocyanate carbon as excellent electrophile can easily be attacked by water as nucleophile. Adding water results in a carbamic acid, which is unstable. Carbamic acids quickly lose carbon dioxide to give an amine. (Clayden et. al, 2009)

Executive summary:

Different scientific sources[1,2] describe the following hydrolysis mechanism for phenyl isocyanates: The isocyanate carbon as excellent electrophile can easily be attacked by water as nucleophile. Adding water results in a carbamic acid, which is unstable. Carbamic acids quickly lose carbon dioxide to give an amine.

Based on this process and due to the lack of data on hydrolysis properties, results from the hydrolysis study of the structural analogue 4-chlorophenyl isocyanate are used to describe the hydrolysis properties of 3,4-dichlorophenyl isocyanate. The chemical structures are closely related, the only difference consists in an additional chlorine substituent present in position 3 in the structure of 3,4-dichlorophenyl isocyanate.

For 3,4-dichlorophenyl isocyanate the fast hydrolysis towards the product 3,4-dichloronaniline (95-76-1) is to be expected.

Reference 2

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Comparable to guideline study with acceptable restrictions

Principles of method if other than guideline:

Investigation on stability in aqueous test solutions.
Comparable to guideline study.

GLP compliance:

no

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

Samples were taken for analysis in intervals of 0 hour to 70 hours after incubation.

Buffers:

buffer solution pH 7.0: 296.3 ml NaOH 0.1 mol/l + 500 ml NaH2PO4 0.1 mol/l adjusted to 1000 ml with deionised water

Details on test conditions:

The test compound (3 mg) was weighed in an Erlenmeyer flask and dissolved in 300 ml of buffer solution ph 7 at ambient temperature (about 25 °C) by means of an ultrasonic bath (10 min) in order to obtain a concentration of 10 mg(l. the liquid was examined visually for undissolved particles, but wasobviously clear.
After preparation, the test solutionwas exposed to a temperature of 25 +/- 0.1 °C in a thermostat. The test war performed in buffer solution pH 7. the test solution and the head space were saturated. The Erlenmeyer flask was irradiated with a lamp of 11 Watt. The intnensity of light, measured on the surface of the flask, was 8000 lux.

Duration:

70 h

pH:

7

Temp.:

25 °C

Remarks:

The test compound itself could not be detected by the HPLC method used.

Transformation products:

yes

No.:

#1

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

Vigourous agitation and ultrasonification for 10 min in order to dissolve 4-chlorophenyl isocyanate (target concentration 10 mg/l, 0.0651 mMol/l) leads to a rapid degradation of the test compound. More than 50 % of the original amount of the test compound has been converted to 4-chloroaniline (4.39 mg/l, 0.0344 mMol/l) at time 0.

pH:

7

Temp.:

25 °C

DT50:

7.3 h

Type:

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

After 70 h, the test was terminated. At this time, the test compound was completely converted to 4-chloroaniline. The concentration of 4-chloroaniline (0.0651 nMol) equalled the initial concentration of 4-chlorophenyl isocyanate (0.0687 mMol).

Conclusions:

There is no test on hydrolysis for 3,4-dichlorophenyl isocyanate available. Results from the hydrolysis study of the structural analogue 4-chlorophenyl isocyanate are used to describe the hydrolysis properties of 3,4-dichlorophenyl isocyanate.

A test was performed in order to examine the stability under conditions simulating those in the environment (pH 7, presence of light and air). The results show that 4-chlorophenyl isocyanate hydrolyses rapidly, forming CO2 and 4-chloroaniline as primary hydrolysis products. Assuming a kinetic function of first order, a half life period of 7.3 h can be calculated (Bayer Industry services, 2004).

Executive summary:

There is no test on hydrolysis for 3,4-dichlorophenyl isocyanate available. Results from the hydrolysis study of the structural analogue 4-chlorophenyl isocyanate are used to describe the hydrolysis properties of 3,4-dichlorophenyl isocyanate.

A test was performed in order to examine the stability under conditions simulating those in the environment (pH 7, presence of light and air). The results show that 4-chlorophenyl isocyanate hydrolyses rapidly, forming CO2 and 4-chloroaniline as primary hydrolysis products. Assuming a kinetic function of first order, a half life period of 7.3 h can be calculated (Bayer Industry services, 2004).

Description of key information

Hydrolysis is not a data requirement for an Art. 18 >1000 t/a registration. Data were included for this endpoint as supporting information for the endpoint water solubility and the aquatic toxicity. 

Different scientific sources describe the following hydrolysis mechanism for phenyl isocyanates: The isocyanate carbon as excellent electrophile can easily be attacked by water as nucleophile. Adding water results in a carbamic acid, which is unstable. Carbamic acids quickly lose carbon dioxide to give an amine.

Based on this process and due to the lack of data on hydrolysis properties, results from the hydrolysis study of the structural analogue 4-chlorophenyl isocyanate are used to describe the hydrolysis properties of 3,4-dichlorophenyl isocyanate. The chemical structures are closely related, the only difference consists in an additional chlorine substituent present in position 3 in the structure of 3,4-dichlorophenyl isocyanate.

A test comparable to guideline study (investigation on stability in aqueous test solutions) was performed in order to examine the stability under conditions simulating those in the environment (pH 7, presence of light and air). The results show that 4-chlorophenyl isocyanate hydrolyses rapidly, forming CO2 and 4-chloroaniline as primary hydrolysis products. Assuming a kinetic function of first order, a half life period of 7.3 h can be calculated (Bayer Industry services, 2004).

For 3,4-dichlorophenyl isocyanate the fast hydrolysis towards the product 3,4-dichloronaniline (95-76-1) is to be expected.

For further details please refer to chapter 13.2.