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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:
20 March 2003 to 25 June 2003
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:
EPA OPPTS 830.7200 (Melting Point / Melting Range)
Deviations:
no
GLP compliance:
yes
Type of method:
capillary method
Melting / freezing pt.:
ca. 186 °C
Decomposition:
yes
Decomp. temp.:
186 °C
Remarks on result:
other: The melting range was dependent upon the heating rate and starting temperature of the equipment. 186 °C is quoted as the starting value for the melting range as the end of the melting range could not be determined.

Table 1: Results

Heating Rate (°C)

Initial Temperature (°C)

Start of Melting (°C)

Comments

Individual

Average

1.0

150.0

180.9

180.8

Discontinued at 190.0 °C. Red discolouration and evidence of sublimination

180.8

180.6

0.2

175.0

181.0

181.0

Discontinued at 185.5 °C. Brown discolouration and evidence of sublimination

180.8

181.1

0.2

177.0

181.3

181.4

Discontinued at 185.3 °C. Brown discolouration and evidence of sublimination

181.3

181.5

0.2

178.0

181.6

181.6

Discontinued at 183.0 °C. Brown discolouration and evidence of sublimination

181.6

181.7

3.0

175.0

186.5

186.4

Discontinued at 190.0 °C. Brown discolouration and evidence of sublimination

186.5

186.1

 

The end of the melting process could not be determined in any of the determinations performed. The discolouration suggested that the test material was decomposing during the melting process.

Additionally, it was noted that the start of the melting process was dependent on both the heating rate and the starting temperature. A faster heating rate yielded a higher value for the start of melting and so did a higher starting temperature. This also indicated that decomposition was occurring alongside melting, since with faster heating rates and higher starting temperature the samples are heated for shorter times before reaching the start of the melting process, thereby reducing the level of any decomposition that may have occurred. The presence of decomposition products would tend to lower the melting range.

Conclusions:
From the determinations where the fastest heating rate were employed, i.e. 3.0 °C/minute, the start of melting was determined to be 186.4 °C. In these determinations the lowest level of decomposition should have occurred. As the melting range of the test material is dependent upon the conditions used for its determination a final value for the start of melting of 186 °C is quoted. The study is considered to be reliable, relevant and adequate for risk assessment purposes.
Executive summary:

The melting behaviour of the test material was determined in accordance with standardised guidelines OECD 102, EU Method A.1 and EPA OPPTS 830.7200 using the capillary method with photocell detection. The test material was found to melt with thermal decomposition, the level of which influences the temperature range within which melting occurs. The melting range was determined to start around 186 °C.

Description of key information

Melting commences around 186 °C (decomposition and sublimation prevents accurate determination), OECD 102, EU method A.1, capillary method, Das 2003

Key value for chemical safety assessment

Additional information

The melting behaviour of the test material was determined in accordance with standardised guidelines OECD 102, EU Method A.1 and EPA OPPTS 830.7200 using the capillary method with photocell detection. The test material was found to melt with thermal decomposition, the level of which influences the temperature range within which melting occurs. The melting range was determined to start around 186 °C.

The study was performed in line with GLP and accepted standardised guidelines with a high standard of reporting. The study was assigned a reliability score of Klimisch 1 and considered suitable for assessment as an accurate reflection of the test substance.

The available data is considered to be complete and the result determined, melting commences around 186 °C (decomposition and sublimation prevents accurate determination), was carried forward for risk assessment.