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Physical & Chemical properties

Endpoint summary

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Description of key information


Direct Red 023 is a odourless red organic solid at 1013 hPa and 20 °C, generally marketed and used in powdered form. Particle size distribution showed that DR023Rm is characterized by particle too large to pass in bronchi and lungs.

Relatrive density was determined by means of a pycnometer and was calculated 1.687 at 20 °C.

Based on structure, the surface activity is nor expected or predicted.

Since it is a solid, properties like vapour pressure, surface tension and flash point can be neglected; viscosity is technically not feasible.


The differential scanning calorimetry method was used for the evaluation of melting and boiling points of the test substance. No endothermic peak corresponding to melting and boiling of the test substance was recorded in the tested temperature range from 25 °C to 600 °C. Between start temperature and 200 °C a first loss of weight was observed, which was attributed to the water evaporation. From the temperature of 230 °C the test substance undergoes to decomposition, connected with the lost of the mass.


DR023 is very soluble in water (23.87 g/l at 20 °C and pH 3.5); taken into account that the substance is a salt coming from strong acid functionalities (sulphonated groups), it is expected that it would be stable in water at different pH conditions, in particular at the biological pH range (i.e. 5-8). The substance contains a number of different ionizable groups, which don't let measure a reliable univocal pKa.

The affinity of DR023Rm with the n-octanol phase is very low, as detemined in the partition ceofficient test, perfomed following the OECD 107 by shake flask method. The logPow resulted lower than -2 (-2.7106 at 20 °C and pH 8.23). Although the value is outside of the applicability domain for the test method, it can be considered as reliable and representative and indicates a very high affility for water in respect than for octanol.


DR023 does not ignite and propagate combustion. The substance contains groups associated with explosive properties, but the exothermic decomposition energy is 231.01 J/g and the onset of the exotermic decomposition is 317.91 °C, thus, according to the preliminary screening procedures described in theAnnex VI, section 3, of the UN Recommendations on the Transport of Dangerous GoodsManual of Tests and Criteria, an explosive potential is not expected.

DR023 does not meet the criteria to be considered as flammable/explosive/oxidising.

Additional information