Sodium thiosulphate

Melting point / freezing point

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

melting point/freezing point

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2010-06-16

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 102 (Melting point / Melting Range)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method A.1 (Melting / Freezing Temperature)

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: OECD 113 (1981) Screening test for thermal stability and stability in air

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

signed, 2009-10-29

Type of method:

other: differential scanning calorimetry (DSC)

Decomposition:

yes

Decomp. temp.:

<= 500 °C

Remarks on result:

other: The test item decomposes during the measurement up to 500°C

A DSC-measurement in closed glass crucibles showed two endothermic peaks in the temperature range 320 -345 °C and 380 -395 °C, respectively. No further effects were observed up to the maximum temperature.

The measurement in an aluminium crucible with a hole showed two endothermic effects in the temperature range 320 to 365 °C and 380 to 405 °C. In the temperature range 425 to 500 °C an exothermic effect with energy of 236 J/g has been observed. An optical inspection after the measurement showed that the test item was still a solid. The test item was discoloured to yellow.

Conclusions:

Sodium thiosulfate shows no melting in the temperature range of 25-500 °C. The observed endothermic effects are presumably assigned to decomposition (disproportionation) or effects like phase transitions.

Reference 2

Endpoint:

melting point/freezing point

Type of information:

other: Handbook data

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Remarks:

From a trusted source acc. to "ECHA, Guidance on information requirements and chemical safety assessment – Chapter R.7a: Endpoint specific guidance"

Qualifier:

no guideline followed

Principles of method if other than guideline:

Not applicable - Handbook data

GLP compliance:

not specified

Type of method:

other: no data

Decomposition:

yes

Decomp. temp.:

100 °C

Conclusions:

According to the reference, sodium thiosulphate decomposes at 100 °C.

Description of key information

Sodium thiosulfate has no melting in the temperature range of 25 - 500 °C. The test item decomposes during the measurement up to 500 °C.

Additional information

For the evaluation of this endpoint data from an experimental study were used as key information, supported by data from the CRC handbook. The study was conducted according to GLP and according to OECD guidelines 113 (screening for thermal stability) and 102 (determination of melting point). The test data are considered as reliable without restrictions.

The thermal stability and the determination of the melting point were carried out by DSC analysis. The test item and the standard material (aluminium oxide) were heated up from ambient temperature to the final temperature (400°C and 500°C, respectively.) at a constant heating rate under nitrogen. Closed class crucibles were used as containers for the screening test and aluminium crucibles with a small hole were used as containers for the main test. The quantity of heat absorbed or released was measured and recorded.

Experimental study results indicated that sodium thiosulfate has no melting point in the temperature range of 25 -500 °C. The test item decomposes during the measurement up to 500°C.

The decomposition is confirmed by the information obtained from the CRC Handbook of Chemistry and Physics. However, according to handbook data, sodium thiosulfate decomposes at 100 °C.