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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:
14 Sept to 21 Sept 2016
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
EU Method A.1 (Melting / Freezing Temperature)
GLP compliance:
yes (incl. certificate)
Remarks:
Hess. Ministerium für Umwelt, Energie, Landwirtschaft und Verbraucherschutz, Wiesbaden, Germany
Type of method:
differential scanning calorimetry
Key result
Melting / freezing pt.:
> 280 °C
Atm. press.:
ca. 1 013 hPa
Decomposition:
yes
Remarks:
substance decomposes before melting up to approx. 280 °C
Decomp. temp.:
>= 280 °C

Evaluation of the data

The evaluation of the data was performed by the software STARe. As result, a thermogram was obtained in which the heat flow** of the investigated sample is given as a function of the temperature. By integration of the heat flow peaks, the energy of the process was obtained.

If the onset temperatures do not differ more than 0.5 K from their mean value, the mean is used as melting point. If the deviation is greater than 0.5 K, a boiling range is specified (lowest to highest onset temperature).

Due to the fact that mixtures do not have a consistent melting point, the lowest onset temperature is used as the beginning of the melting range.

If the test item decomposes before reaching its melting point, the temperature at the start of the decomposition has to be specified.

Results

The thermogram of the DSC runs PN11868 and PN11879 show in the temperature range of 280 -310 °C a sharp endothermic effect. The test item welled out of the test cell during the test and turned black.

Table: Results of the DSC-measurements

No.

Sample weight / mg

Onset of effect / °C

Range of effect / °C

Weight loss / mg

PN11868

16.50

289.99

290 – 310 (endo)

‘---*

PN11879

7.08

288.32

280 – 310 (endo)

3.16

* Not determined

The endothermic effect in the temperature range of 280 – 310 °C cannot be clearly assigned to the melting of the test item, since test item welled out of the test cell during the test and turned black. Due to the fact that there are no further exothermal effects afterwards, it can be assumed that the test item decomposes accompanied with a formation of gaseous decomposition products before reaching its melting point. This evaporation is detected as an endothermic effect in the DSC measurements and may overlay the exothermic decomposition. This behavior was also observed in the test in the Grewer oven (see report CSL-16-1457.03, Auto ignition).

Due to this, the test item has no melting point up to its decomposition starting at a temperature of approx. 280 °C.

** = negative heat flow for endothermic processes, positive heat flow for exothermic processes.

Description of key information

The substance dehydroacetic acid sodium salt does not melt up to the decomposition temperature of 280 °C at atmospheric pressure (OECD 102, EU A.1, DSC)

Key value for chemical safety assessment

Additional information