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Physical & Chemical properties

Partition coefficient

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Reference
Endpoint:
partition coefficient
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Justification for type of information:
1. HYPOTHESIS FOR THE ANALOGUE APPROACH
Data for butane-1,3-diol (CAS No. 107-88-0) is used to address the physical-chemical property data requirements for (R)-(-)-butane-1,3-diol (CAS No. 6290-03-5) in an analogue read-across approach. The basis for this read-across approach is the extreme structural similarity of the source and target substances, in that the source substance is a racemic mixture of a pair of enantiomers, whereas the target substance is solely the R-enantiomer of that source pair. Two compounds that are enantiomers of each other have the same physical properties, except for the direction in which they rotate polarized light and how they interact with different optical isomers of other compounds (ECHA, 2008). On this basis, the physical-chemical property values available for the source substance are directly applicable to the target substance.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Target Substance: (R)-(-)-butane-1,3-diol (228-532-0; 6290-03-5) ≥ 99% (99-100%)
Source Substance: (R/S)-Butane-1,3-diol (203-529-7; 107-88-0) 100%
[See attached JUSTIFICATION FOR READ-ACROSS OF PHYSICAL-CHEMICAL PROPERTY DATA for further details.]

The target substance is known to be of high purity (≥99 % w/w), so the low levels of impurities it could contain are not expected to substantially affect its physical-chemical properties. The purity of samples of the source material used to generate handbook data is not specifically known, but it is assumed that they would not have been sufficiently impure as to substantially affect the property values presented in the handbooks. On this basis, the applicability of the data on the source substance to the target substance is not expected to be compromised by the presence of impurities in either substance.

3. ANALOGUE APPROACH JUSTIFICATION
The basis for this read-across approach is the extreme structural similarity of the source and target substances. Specifically, the source substance is a racemic mixture of a pair of enantiomers, whereas the target substance is solely the R-enantiomer of that source pair. The source substance is therefore nominally comprised 50% of the target substance itself (the R-enantiomer), and 50% of its mirror image (the S-enantiomer), which differs from the target substance only in the chirality of one carbon atom. The selection of this source substance is justified on the basis that there is no other source substance that could possess a greater degree of structural similarity to the target substance.

Enantiomers are two stereoisomers that are related to each other by a reflection: they are mirror images of each other. Every stereocentre in one has the opposite configuration in the other. Two compounds that are enantiomers of each other have the same physical properties, except for the direction in which they rotate polarized light and how they interact with different optical isomers of other compounds (ECHA, 2008).

4. DATA MATRIX
It is clear that for all of the following physical property values required by Annexes VII and IX:
7.2 melting/freezing point;
7.3 boiling point;
7.4 relative density;
7.5 vapour pressure;
7.6 surface tension;
7.7 water solubility;
7.8 n-octanol/water partition coefficient;
7.16 dissociation constant; and
7.17 viscosity
values generated on the source substance will be directly applicable to the target substance.

Similarly, since flash point (7.9) and self-ignition temperature (7.12) are measures of the reactivity of a substance towards achiral atmospheric O2, these parameters will also be common to both the source and target substances, so values generated on the source substance will again be directly applicable to the target substance.

Weight of Evidence Approach
This endpoint study record is part of a Weight of Evidence approach comprising a two read-across (this study and another). Both data sources agree in the estimated value and are sufficient to fulfil the information requirements as further explained in the provided endpoint summary.

REFERENCES
ECHA (2008). Guidance on information requirements and chemical safety assessment. Chapter R.6: QSARs and grouping of chemicals. May 2008. Available at: https://echa.europa.eu/documents/10162/13632/information_requirements_r6_en.pdf [Last accessed April 26, 2016].
Reason / purpose:
read-across source
Related information:
Composition 1
Reason / purpose:
read-across source
Related information:
Composition 1
Reason / purpose:
read-across source
Related information:
Composition 1
Reason / purpose:
read-across source
Related information:
Composition 1
Reason / purpose:
read-across source
Related information:
Composition 1
Reason / purpose:
read-across source
Related information:
Composition 1
Test material information:
Composition 1
Specific details on test material used for the study:
(R)-(-)-Butane-1,3-diol value is read-across from supporting (R/S)-butane-1,3-diol (203-529-7; 107-88-0) data
Key result
Type:
log Pow
Partition coefficient:
>= -0.92 - <= -0.08
Remarks on result:
not measured/tested
Conclusions:
The partition coefficient data generated on the source substance [(R/S)-butane-1,3-diol (203-529-7; 107-88-0)] will be directly applicable to the target substance [(R)-(-)-butane-1,3-diol]. The n-octanol-water partition coefficient is predicted to be ≥-0.92 to ≤-0.08.

Description of key information

The partition coefficient data generated on the source substance [(R/S)-butane-1,3-diol (203-529-7; 107-88-0)] will be directly applicable to the target substance [(R)-(-)-butane-1,3-diol].  Six source values were referenced:

- Read-Across experimental value from data collection log: Log Kow = -0.92

- Read-Across experimental value from data collection log: Log Kow = -0.9

- QSAR prediction: -0.29

- QSAR prediction: -0.29

- QSAR prediction: -0.08

- QSAR prediction: -0.46

The n-octanol-water partition coefficient is predicted to be ≥-0.92 to ≤-0.08.

HYPOTHESIS FOR THE ANALOGUE APPROACH

Data for butane-1,3-diol (CAS No. 107-88-0) is used to address the physical-chemical property data requirements for (R)-(-)-butane-1,3-diol (CAS No. 6290-03-5) in an analogue read-across approach. The basis for this read-across approach is the extreme structural similarity of the source and target substances, in that the source substance is a racemic mixture of a pair of enantiomers, whereas the target substance is solely the R-enantiomer of that source pair. Two compounds that are enantiomers of each other have the same physical properties, except for the direction in which they rotate polarized light and how they interact with different optical isomers of other compounds (ECHA, 2008). On this basis, the physical-chemical property values available for the source substance are directly applicable to the target substance.

Key value for chemical safety assessment

Log Kow (Log Pow):
-0.9
at the temperature of:
25 °C

Additional information