Registration Dossier

Physical & Chemical properties

Endpoint summary

Administrative data

Description of key information

Additional information

At standard conditions, the natural occurring substance L-tryptophan exists as white, fluorescent leaflets. The melting point of L-tryptophan is reported to be in the range between 290 and 292°C (decomposition starts at 281°C). According to REACH Regulation (Annex VII, 7.3, column 2), the study on the boiling point does not need to be done if the substance decomposes before the boiling point is reached. In the frame of melting point determination, decomposition of L-tryptophan was observed at 281°C. The relative density D (22/4) was determined to be 1.39. The measuring of the particle size distribution of L-tryptophan resulted in a median diameter of 40.49 µm, and the particle size distributions D10 and D90 were determined to be 11.38 µm and 69.22 µm, respectively. Based on the chemical structure a low volatility is to be expected. This assumption is confirmed by calculation. The calculation via EPIWIN and ACD resulted in vapour pressures of 2.6 x 10E-9 and 1.1 x 10E-8 hPa at 25°C, respectively. The n-octanol/water partition coefficient (log Pow) was determined to be -1.06. The water solubility of L-tryptophan is reported to be 11.4 g/L at 25°C and pH values in the range of 5.5 to 7. L-Tryptophan has no surface-active properties (surface tension: >60 mN/m at 20°C). According to Guidance on information requirements and chemical safety assessment, chapter R.7a: Endpoint specific guidance (R.7.1.9.4), the flash point is only relevant to liquids and low melting point solids. Therefore, the determination of the flash point is not required as L-tryptophan is a solid at standard conditions with a high melting point (ca. 290°C). The self-ignition temperature ("self-heating limit temperature") of L-tryptophan (deposited dust) determined in a 1 -L wire basket is reported to be 154°C. In the Grewer oven screening test, a minor exothermic reaction was observed starting at 205°C (temperature increase of ca. 5°C in comparision to the reference substance graphite). In the temperature range between 238 and 265°C, the test substance showed an endothermic reaction and between 265 and 400°C the temperature of the sample did not deviate from the oven temperature. At test termination the sample basket was empty. No self-ignition temperature could be found in the Grewer-oven screening test up to 400°C. Based on the experimental findings in respect to flammability, L-tryptophan was grouped into the class of substances having a combustion factor of 3 (local burning with at the most minor propagation; no propagation of fire). According to REACH Regulation (Annex VII, 7.11, column 2), the study on explosiveness does not need to be done if the substance does not contain chemical groups indicating explosive properties. L-Tryptophan does not contain any chemical groups indicating explosive properties. According to REACH Regulation (Annex VII, 7.13, column 2), the study on oxidising properties does not need to be done for substances which do not react exothermically with combustible substances based on their structure. L-Tryptophan does not contain any chemical groups indicating oxidising properties. According to REACH Regulation (Annex IX, 7.15, column 1), the study on the stability in organic solvents and identity of relevant degradation products does only to be done if the stability is regarded as a substantial property of the substance. The stability of L-tryptophan is considered to be not critical. The dissociation constants of L-tryptophan are reported to be 2.38 (pK1) and 9.39 (pK2). According to Guidance on information requirements and chemical safety assessment, chapter R.7a: Endpoint specific guidance (R.7.1.18.4), viscosity is only relevant to liquids. Therefore the determination of the viscosity is not required.