p-benzoquinone dioxime

Melting point / freezing point

Link to relevant study record(s)

Reference

Endpoint:

melting point/freezing point

Type of information:

experimental study

Adequacy of study:

key study

Study period:

02-02-2018 to 14-03-2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Guideline study performed under GLP. All relevant validity criteria were met.

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:

differential scanning calorimetry

Melting / freezing pt.:

> 237 °C

Atm. press.:

ca. 101.3 kPa

Decomposition:

yes

Remarks:

The DSC was not indicative of sublimation (phase change), the DSC was indicative of a classic decomposition curve and the TGA result is reported as teh decomposition temperature.

Decomp. temp.:

ca. 237 °C

Sublimation:

no

Remarks:

The TGA and DSC was not indicative of sublimation (phase change)

Remarks on result:

other: measurement under a flow of nitrogen

Preliminary study (TGA)

During heating, and starting at 225°C, the weight of the sample decreased significantly. A sharp spike was observed at approximately 237°C. At 238°C, the sample weight had decreased by 27%. After the experiment, grey residue was observed on the lid of the sample container and a black residue remained in the sample container (original colour: brown). The change of the colour indicated reaction and/or decomposition of the test item.

Main study (DSC)

- Experiment 1: During heating, an exothermic peak was observed starting at 175°C. The exothermic effect was due to reaction and/or decomposition of the test item. After the experiment, a black residue remained in the sample container (original colour: brown). The change of the colour indicated reaction and/or decomposition of the test item. As a result of the DSC curve indicative of decomposition a repeat experiment was not performed.

 

Applicant assessment indicates: No melting temperature could be determined as the test item decomposed during heating. Expert judgement indicates that the approximate decomposition temperature was ca. 237 °C (ca. 510K) as indicated in the TGA preliminary experiment. TGA as a technique is frequently used to study decomposition of substances. This is its purpose as a preliminary test for safety prior to the OECD TG 102 guideline: DSC definitive test. DSC as a technique is frequently used to measure MP, BP and Vapour Pressure properties and not per se, chemical decomposition or its kinetics. The TGA result is indicative of the actual test item decomposition temperature ca. 237 °C (ca. 510K), prior to test item melting (phase change).

Conclusions:

The melting temperature of the test item is > 237 °C but no actual melting point or range could not be determined due to decomposition. The TGA result is indicative of the actual test item decomposition temperature ca. 237 °C (ca. 510K), prior to test item melting (phase change).

Executive summary:

The melting temperature was studied using OECD TG 102 and EU Method A.1 with the Differential Scanning Calorimetry method under GLP. The guideline defines the melting temperature as: the temperature at which the phase transition from solid to liquid state occurs at atmospheric pressure and this temperature ideally corresponds to the freezing temperature. In a preliminary TGA screening test, 1.66 mg test item was heated at a rate of 20°C per minute to 549°C. The experiments were performed under a flow of nitrogen at atmospheric pressure. At this point 51% weight loss of the test item was observed. After the experiment, the sample was cooled to and equilibrated at 75°C and the consistency of the test item was determined. During heating, and starting at 225°C, the weight of the sample decreased significantly. A sharp spike was observed at approximately 237°C. At 238°C, the sample weight had decreased by 27%. After the experiment, grey residue was observed on the lid of the sample container and a black residue remained in the sample container (original colour: brown). The change of the colour indicated reaction and/or decomposition of the test item. Within the definitive DSC test, 1.00 mg test item was heated from 25°C at +20°C per minute to 238°C. The experiments were performed under a flow of nitrogen at atmospheric pressure. During heating, an exothermic peak was observed starting at 175°C. The exothermic effect was due to reaction and/or decomposition of the test item. After the experiment, a black residue remained in the sample container (original colour: brown). The change of the colour indicated reaction and/or decomposition of the test item. The overall conclusions were: in the preliminary TGA test, at temperatures of ca. 237 °C (ca. 510K) the onset of reaction and/or decomposition of the test item was observed. In the definitive DSC test, temperatures of > 175°C (> 448K) reaction and/or decomposition of the test item was observed. Melting of the test item was not observed below the temperature at which reaction and/or decomposition started. Under the conditions of this study, the test item has no melting temperature.

Applicant assessment indicates: that the approximate decomposition temperature was ca. 237 °C (ca. 510K) as indicated in the TGA preliminary experiment. TGA as a technique is frequently used to study decomposition of substances. This is its purpose as a preliminary test for safety prior to the OECD TG 102 guideline: DSC definitive test. DSC as a technique is frequently used to measure MP, BP and Vapour Pressure properties and not per se, chemical decomposition or its kinetics. Whereas, TGA is frequently used to quantify oxidation and/or decomposition of solids. By expert judgement, the TGA result is indicative of the actual test item decomposition temperature ca. 237 °C (ca. 510K), prior to test item melting (phase change). The melting temperature of the substance is > 237 °C but no actual melting point or range could not be determined due to decomposition.

Description of key information

Mp: > 237 °C (> 510K) at 1 atmosphere and at ca. 237 °C (510K) the substance thermally decomposes, OECD TG 102 - DSC Method incorporating TGA preliminary screening, 2018

Additional information

The melting temperature was studied using OECD TG 102 and EU Method A.1 with the Differential Scanning Calorimetry method under GLP. The guideline defines the melting temperature as: the temperature at which the phase transition from solid to liquid state occurs at atmospheric pressure and this temperature ideally corresponds to the freezing temperature. In the preliminary TGA test, at temperatures of ca. 237 °C (ca. 510K) the onset of reaction and/or decomposition of the test item was observed. In the definitive DSC test, temperatures of > 175°C (> 448K) reaction and/or decomposition of the test item was observed. Melting of the test item was not observed below the temperature at which reaction and/or decomposition started. Under the conditions of this study, the test item has no melting temperature.

 

Applicant assessment indicates: that the approximate decomposition temperature was ca. 237 °C (ca. 510K) as indicated in the TGA preliminary experiment. TGA as a technique is frequently used to study decomposition of substances. This is its purpose as a preliminary test for safety prior to the OECD TG 102 guideline: DSC definitive test. DSC as a technique is frequently used to measure MP, BP and Vapour Pressure properties and not per se, chemical decomposition or its kinetics. Whereas, TGA is frequently used to quantify oxidation and/or decomposition of solids. By expert judgement, the TGA result is indicative of the actual test item decomposition temperature ca. 237 °C (ca. 510K), prior to test item melting (phase change). The melting temperature of the substance is > 237 °C but no actual melting point or range could not be determined due to decomposition. This conclusion also corresponds to historic published literature in Weast et al., CRC Handbook of Chemistry and Physics, (1979) which quotes a decomposition temperature of 240°C for the substance.

 

References:

1. Anon., Melting Point study, OECD TG 102, 2018

2. Weast, R.C., ed. (1979) CRC Handbook of Chemistry and Physics, 60th ed. page C-204

3. IARC monographs on the evaluation of the carcinogenic risk of chemicals to humans, volume 28 and 29, (1982)