Registration Dossier

Physical & Chemical properties

Endpoint summary

Administrative data

Description of key information

Additional information

Hydroquinone is an odorless organic, crystalline solid that can be found as needles, prisms and monoclinic prisms. It can be colorless, light-tan, light-grey or white. Hydroquinone was reported to have a melting point of 172.3°C and a boiling point of 287°C at 1013 hPa. The relative density of Hydroquinone was reported as 1.33 at a temperature of 15°C. The particle size distribution of extra pure and premium hydroquinone was determined via laser diffraction. The X10, X50, and X90 values were determined to be 136.4, 286.0, and 478.8 µm for the extra pure quality and 125.8, 281.0, and 481.8 µm for the premium quality, respectively. The amount of fines <100 µm were found to be 4 (extra pure) and 5% w/w (premium) and the classes of particles < 105 µm were determined to be 4.4 (extra pure) and 5.95% in volume (premium). Vapour pressure was found to be 0.000032 hPa at 25 °C (extrapolated based on measured values). The measured log Pow was reported to be 0.59. Hydroquinone was reported to be very soluble in water with a solubility of 72 g/L at a temperature of 25°C. According to REACH regulation (Annex VII, 7.6, column II), the study on surface tension does not need to be conducted if based on the molecular structure surface-active properties are to be expected or can be predicted. For Hydroquinone no surface-active properties are to be expected. Using the closed cup method, hydroquinone was reported to have a flash-point of 165°C at standard pressure (1013 hPa). The self-ignition temperature was reported as 515 °C at standard pressure. Hydroquinone can not be considered as highly flammable. Explosive properties were not reported because, according to REACH regulation (Annex VII, 7.11, column II), the study on explosiveness does not need to be done as Hydroquinone has no functional groups indicating explosive properties. However, because the substance is a solid, for process safety purposes the Minimum Ignition Energy was determined on the substance as produced, as well as on normalised samples obtained after particle size reduction and sieving to 63 um, to assess the dust explosibility potential. The MIE for the normalised samples were 1-3 mJ, and 8-10 mJ for the substance as produced, indicating a high sensitivity to ignition. According to REACH regulation (Annex VII, 7.13, column II), the study on oxidising properties does not need to be done for Hydroquinone as the substance is incapable of reacting exothermically with combustible materials. On the basis of the chemical structure the substance does not contain any oxygen or halogen atoms that are chemically bonded to nitrogen or oxygen. According to REACH regulation (Annex IX, 7.15, column I) the study on stability in organic solvents does not need to be conducted as stability in organic solvents is not regarded as critical. Hydroquinone was reported to have dissociating properties. A pK1 of 9.91 and a pK2 of 11.56 were found, both at a temperature of 20°C. According to REACH Regulation (Annex XI, 1.) a test for the determination of the viscosity is scientifically not necessary because viscosity refers to liquids. The test item is a solid at ambient temperature. Therefore, determination of viscosity is not required.