Phenyl isocyanate

Partition coefficient

Link to relevant study record(s)

Reference

Endpoint:

partition coefficient

Type of information:

(Q)SAR

Adequacy of study:

key study

Study period:

2012

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

accepted calculation method

Justification for type of information:

QSAR prediction

Guideline:

other: REACH guidance QSARs R6, May/July 2008

Principles of method if other than guideline:

Estimation Program Interface EPI-Suite version 4.1: KOWWIN for estimating the logarithmic octanol-water partition coefficient (log Kow).
The Estimation Programs Interface was developed by the US Environmental Agency's Office of Pollution Prevention and Toxics and Syracuse Research Corporation (SRC).© 2000 - 2011 U.S. Environmental Protection Agency for EPI SuiteTM (Published online in January 2011).

GLP compliance:

no

Type of method:

other: QSAR

Partition coefficient type:

octanol-water

Type:

log Pow

Partition coefficient:

2.59

Temp.:

25 °C

pH:

7

Remarks on result:

other: Calculation based on room temperature and neutral pH condition

Validity of model:

1. Defined Endpoint: Octanol-water partition coefficient

2. Unambiguous algorithm: The molecule is separated into distinct atom/fragments using an Atom/Fragment Contribution method. Based on structure of the molecule, the following fragments were applied: aromatic carbon, isocyanate, aromatic attach

is applied. The number of times of the fragments that occurs in the structure of the substance applied by the program is verified.

3. Applicability domain: With a molecular weight of 119.12 g/mole the substance is within the range of the training set (18.02 - 719.92) as well as in the range of the validation set (27.03 - 991.15).

It is considered that the estimated coefficient applied for the “isocyanate, aromatic attach”-fragment leads to an undefined uncertainty. However, as isocyanates are known to hydrolyse in the presence of water and any decomposition of the substance is not taken into account by the program, the estimated value for log Kow is only of theoretical interest.

4. Statistical characteristics: Correlation coefficient of the total training set r² = 0.982; Correlation coefficient of the total validation set r² = 0.943.

5. Mechanistic interpretation: The structural fragments used as descriptors reflect the lipophilic or hydrophobic properties of the substances, and so the octanol-water partition coefficient.

6. Adequacy of prediction: The result for phenyl isocyanante falls within the applicability domain described above and the estimation rules applied for the substance appears appropriate. Therefore the predicted value can be considered reliable yielding a useful result for further assessment.

Conclusions:

The QSAR determination of the logarithmic octanol-water partition coefficient for phenyl isocyanante using the model KOWWIN included in the Estimation Program Interface (EPI) Suite v4.1 revealed a value of 2.59 of the substance. The predicted value can be considered reliable yielding a useful result for further assessment.

Executive summary:

The logarithmic octanol-water partition coefficient (log Kow) for phenyl isocyanante was predicted using the QSAR calculation of the Estimation Program Interface (EPI) Suite v 4.1. The log Kow was estimated to be 2.59. The predicted value can be considered reliable yielding a useful result for further assessment.

Description of key information

The QSAR determination of the logarithmic octanol-water partition coefficient for phenyl isocyanante using the model KOWWIN included in the Estimation Program Interface (EPI) Suite v4.1 revealed a value of 2.59 of the substance.

The partition coefficient of aniline, the hydrolysis product of phenyl isocyanate, was measured as log Pow of 0.91 at 25 °C.

Key value for chemical safety assessment

Log Kow (Log Pow):

2.59

at the temperature of:

25 °C

Additional information

The QSAR determination of the logarithmic octanol-water partition coefficient for phenyl isocyanante using the model KOWWIN included in the Estimation Program Interface (EPI) Suite v4.1 revealed a value of 2.59 of the substance.

According to handbook data, isocyanates react rapidly with water forming aminic structures as well as carbamic acids, which are mostly unstable, and ureas under release of carbon dioxide. Monitoring the amine formation in hydrolysis studies gives a picture of the degradation of the isocyanate. This behaviour of isocyanates has been used in studies to determine the rate of degradation*. In Guidance on IR & CSA Chapter R.6 it is mentioned that degradation products instead of parent substance can be investigated for ecotoxicological effects if the hydrolysis is very rapidly (t1/2 <1 h), OECD Guidance Document on Aquatic Toxicity Testing of Difficult Substances and Mixtures (2000) and Guidance on IR & CSA Chapter R.7b state the same. As phenyl isocyanate hydrolyses to aniline this is the ecotoxicological relevant species. Concluding, tests performed using the corresponding amine can equally be used to assess the ecotoxicological hazards of phenyl isocyanate. An underestimation of environmental hazards is thus avoided supporting a conservative and thus protective hazard assessment.

* Bayer Industry Services (2004), 4-chlorophenyl-isocyanate: Investigation on Stability in Aqueous Test Solutions. Project No: 200300181. Leverkusen, Germany.

Bayer Industry Services (2003), Isopropyl isocyanate: Investigation on Stability in Aqueous Test Solutions. Project No: 200300095. Leverkusen, Germany.