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Physical & Chemical properties

Melting point / freezing point

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Reference
Endpoint:
melting point/freezing point
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
other:
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.


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:
data waiving: supporting information
Related information:
Composition 1

Description of key information

The study does not need to be conducted below a lower limit of -20 °C.  The melting point of the racemate is <-50 °C.

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

Melting / freezing point at 101 325 Pa:
-50 °C

Additional information