Registration Dossier

Physical & Chemical properties

Endpoint summary

Administrative data

Description of key information

Additional information

Appearance/physical state/colour

On the basis of physical observation and using the sense of smell, clioquinol was found to be a pale yellow organic amorphous solid with no odour at 24°C and 990 hPa.

Melting point/freezing point

No. of studies reviewed for Melting point endpoint from reliable sources having Klimish rating 2 and 4.

The summary of the results are presented below


Sr. no.

Endpoint name





Melting point



CRC Handbook of Chemistry and Physics


Melting point



Journal of Organic Chemistry


Melting point



Pakistan Journal of Scientific and Industrial Research and Pharmaceutical Central Hall



Based on the various weight of evidence studies the melting point of the test substance clioquinol varies between 178 to 181 degC.


Boiling point

Boiling point of clioquinol was estimated to be 365.31°C by means of adaptated stein and brown method.


The bulk density of clioquinol by the mass by volume method was found to be 1.882 g/cm3 at room temperature of 24°C .This value when converted at 20 degC is equivalent to 1.5683.

Particle size distribution (Granulometry)

The particle size distribution (granulometry) of clioquinol by the sieve analysis method was found to be in the range of 75 micrometer to 500 micrometer. Majority of the particles were found to be in the size more than 150 (40.36%) - 500 (20.25%) micrometer in size.

Vapour pressure

Vapour pressure of clioquinol was estimated to be 0.0000479 Pa at 25 deg C by means of modified grain method. The Supporting study shows value different from key study which could be due to difference in the estimation conditions. However for the purpose of chemical safety assessment key study value shall be considered.

Partition coefficient

The experimental value of octanol water partition co-efficient (log Pow) of clioquinol is 1.5233 at 24 degC and pH of 4.7.This value indicates that clioquinol is relatively hydrophobic in nature.

Water solubility

The experimental value of the water solubility of clioquinol was found to be 4600 mg/L at 24 degC indicating that it is soluble in water.

Solubility in organic solvents / fat solubility

Gravimetric method was used to determine the solubility of the substance in organic solvent. The experimental value of solubility of clioquinol in methanol at 24 degC was found to be 1400 mg/L indicating that the substance is soluble in methanol.Using the Soxhlet/Solvent extraction method the solubility of the substance in Petroleum ether is observed to be 2000 mg/L at 24 °C, indicating that the substance is soluble in petroleum ether. The solubility value of clioquinol in petroleum ether at 20 degC is equivalent to a value of 1666.66 mg/L.

Surface tension

In accordance with Column 2 adaptation statement of REACH Annex VII, information requirement 7.6, this end point was considered for waiver since surface activity was not a desired property of clioquinol.

Flash point

In accordance with Section 2 of REACH Annex XI, information requirement section 7.9, this study does not need to be conducted based on the physical state of the molecule. According to ECHA guidance, flash point is only relevant to liquids.Therefore this study was considered for waiver.

Auto flammability

Clioquinol did not catch fire on being exposed to air at room temperature of 24 degC and atmospheric pressure of 990 hPa. This indicates that Clioquinol is not auto-flammable.


From the experimental values of flammability, clioquinol ignited when the flame of bunsen burner having temperature of 950 degC was brought in contact with it. Thus it can be concluded that clioquinol is flammable only at high temperature of about 950 degC. However since such high temperatures are not found under normal circumstances of transportation and use, clioquinol was considered non-flammable for chemical safety assessment.


According to theoretical considerations based on chemical structure, clioquinol does not possess explosive properties. The reason for this is there are no chemical groups associated with explosive properties in clioquinol Thus, as per column 2 of Annex VII this end point was considered for waiver.

Oxidising properties

Clioquinol was found to have mild oxidising property since 334.0 ml of KMnO4 was required for getting the end point of the redox titration for 100 g of clioquinol. Thus, the chemical is considered as non-oxidising for the purpose of classification.

Stability in organic solvents and identity of relevant degradation products

Clioquinol was found to be stable in organic solvent dichloro methane and no degradation products were formed after 24 hours as evident from the GC-MS chromatogram obtained at 0 hours and that obtained after 24 hours.


1% by volume solution of clioquinol was found to exhibit a pH of 3.42 at 21 degC. Thus 1% by volume solution of clioquinol is acidic in nature.

Dissociation constant

The experimental pKa value for clioquinol was found to be 0.0000045133333333 (average pKa value) at 24 degC indicating that it has dissociation properties. This value at 20 deg C is equivalent to 0.000003761111111083.


This end point was considered for waiver since viscosity is an inherent property of a liquid that offers resistance to its flow and clioquinol is a solid substance and hence this testing was considered scientifically unjustified for clioquinol.