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Physical & Chemical properties

Melting point / freezing point

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Reference
Endpoint:
melting point/freezing point
Type of information:
experimental study
Adequacy of study:
key study
Study period:
02-05 October 2015
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
The study was conducted according to an internationally recognised method, and under GLP. No deviation was reported. Test substance is adequately specified with purity. Therefore full validation applies.
Qualifier:
according to
Guideline:
OECD Guideline 102 (Melting point / Melting Range)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method A.1 (Melting / Freezing Temperature)
Deviations:
no
Qualifier:
according to
Guideline:
EPA OPPTS 830.7200 (Melting Point / Melting Range)
Qualifier:
according to
Guideline:
other: CIPAC MT 1 (2009): Freezing Point
Principles of method if other than guideline:
Not applicable
GLP compliance:
yes (incl. certificate)
Remarks:
inspected on January 22 and 23, 2013 / signed on March 22, 2013
Type of method:
differential scanning calorimetry
Specific details on test material used for the study:
Storage conditions of test material: 11-25 °C, dry, keep container closed.
Melting / freezing pt.:
-39 - 20 °C
Atm. press.:
1 009 hPa
Decomposition:
no
Remarks on result:
other: Freezing point
Melting / freezing pt.:
-38 - 23 °C
Atm. press.:
1 009 hPa
Decomposition:
no
Remarks on result:
other: Melting point

Table 4.2/1: Results of the DSC-measurements

 

No.

Sample

weight (mg)

Onset of Effect (°C)

Range of effect (°C)

Air pressure (hpa)

Remark

PN9730

14.75

20.07

21 to 22 (exo)

1009.3

Cooling

-38.41

-39 to -38 (exo)

-37.72

-50 to -25 (endo)

Heating

-8.94

-10 to 10 (endo)

22.42

15 to 35 (endo)

285.85

230 to 380 (endo)

PN9731

15.04

19.34

21 to 22 (exo)

1009.0

Cooling

-38.68

-39 to -38 (exo)

-37.90

-50 to -25 (endo)

Heating

-9.12

-10 to 10 (endo)

22.69

15 to 35 (endo)

283.95

230 to 370 (endo)

 

During the cooling to a temperature of -100 °C two sharp exothermic effects could be observed in a temperature range from -39 to 22 °C, which can be assigned to the freezing of the test item. As there are two exothermic signals, the test item has a freezing range from -39 to 20 °C by evaluating minimum and maximum onset temperatures of the effects. During the subsequent heating phase three distinct endothermic effects were observed in the temperature range from -50 to 35 °C, which can be assigned to the melting of the test item. As there are three endothermic signals, the test item has a melting range from -38 to 23 °C by evaluating minimum and maximum onset temperatures of the effects.

The observation of more than one melting point might be caused by the existence of different isomers of the test item. Here, for example, the keto-enol automatism can lead to three different stable isomers of the test substance. Another explanation might be the existence of ring conformational isomerism which can lead to several stable conformers.

Executive summary:

The freezing and melting points of the test substance were determined under GLP according to EU Method A.1 and OECD 102, by differential scanning calorimetry (DSC). Two main runs were performed, and the average of the onset temperatures was retained.

The test item undergoes freezing in two steps at +20°C and -39°C, and melting in three steps from -38 to 23 °C, at atmospheric pressure (1009 hPa) under nitrogen. The phenomenon may be due to isomerism (or crystal rearrangement) of the substance.

Description of key information

2-step Freezing in the range from +20°C to -39°C.
3-step Melting in the range from -38°C to 23°C (both results at atmospheric pressure 1009 hPa under nitrogen)

Key value for chemical safety assessment

Additional information

A fully reliable experimental study, conducted according to a recognized OECD/EC method and under GLP, is available. It is considered as a key study. As both transitions occur in multi-step, the results are expressed as a melting/freezing range, and cannot be retained as (single) key value.