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Physical & Chemical properties

Endpoint summary

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Due to the production process of the alkylamidopropyl betaines, the technical grade product is obtained as aqueous solution (active matter: ca. 20-40%). In general, the pure substances are not isolated from the aqueous solution and are used and/or marketed as aqueous solution. Only for the purpose of determination of specific physico-chemical properties, purified fractions of the test substance were manufactured and selected endpoints were measured.

Under standard conditions, AAPB is an organic solid. A melting and a boiling point were not identifiable via DSC measurements due to decomposition of the test substance. The melting points of the C8/C18 (208°C), C8/10 (55 -60°C), and C12/14 (69 -72°C) fractions of Coco AAPB determined via the capillary method are judged as not reliable, as the method does not distinguish between a real melting process and a reaction/decomposition process and as comparable temperatures were found as decomposition temperature in the DSC measurements. The relative density D (4/20) was determined to be in the range between 1.15 and 1.20.

According to REACH Regulation (Annex VII, 7.14, column 2), the study on particle size distribution (granulometrie) does not need to be conducted, as the AAPBs are marketed or used only as liquids (aqueous solution).

According to REACH Annex XI, 2. the determination of the vapour pressure of AAPB is not necessary as it is technically not possible: the expected value of vapour pressure for the pure substance cannot be measured due to residual content of solvent (water, isopropanole) which results in a higher solvent vapour pressure than test substance vapour pressure. The residual content of solvent cannot be reduced below the limit of measurement with reasonable effort. In a supporting study conducted according to OECD Guideline 104, a very low vapour pressure (vp: 0.00 31 hPa) was determined for the C8/10 fraction of Coco AAPB. This fraction covers the residual content of solvent (water, isopropanole). The value of vapour pressure for the pure substance cannot be measured. However, the vapour pressure of AAPBs is expected to be low.

The log Kow values were calculated for all fatty acid chain lengths, separately, using the chemical properties prediction software ACD/Labs v12 and the experimental data of C12 AAPB. The calculated log Kow value obtained via the equation of Gerstl (input parameter: Koc determined by measurement of C12 AAPB) was used as training structure for the ACD software. For experimental data input to ACD/Labs, i. e. C12 AAPB, the experimentally derived log Koc value of 2.5 was used for calculation of the log Kow according to Gerstl (1990) formula, which resulted in a log Kow of 3.54. The calculation via ACD yielded log Kow values of 1.79 (C8), 2.81 (C10), 3.54 (C12), 5.13 (C14), 6.15 (C16), and 7.17 (C18), respectively. It can be assumed that unsaturation in the fatty acid moiety (C18 derivate) increases hydrophilicity and therefore a slightly lower log Kow value is to be expected. Therefore, it can be assumed that the aforementioned n-octanol-water partition coefficients (log Kow) are valid for all AAPBs. For derivation of toxicity data by EUSES (derivation of PNECs for marine and inland soil and sediment) a weighted mean log Kow was calculated according to weight fractions stated by HERA.2007, resulting in a weighted mean log Kow of 4.2317 for AAPB.

As the test substance is visually unlimited soluble in water (formation of micelles), the OECD Guideline 105 (column elution method and flask method) is not applicable. Therefore it was tried to determine the water solubility via the measurement of the critical micelle concentration (CMC). CMC measurements were carried out using the autodilution method (reverse CMC) and an average surface tension vs. concentration curve was constructed. A well-defined CMC was not observed. However, this could not be expected for a multi component substance; every component will have a different CMC if measured individually as a pure substance. Based on the CMC, a water solubility of AAPB molecules is ≤ 400 mg//L at 20°C. A surface tension ranging from 30.9 to 32.0 mN/m at 20°C was measured via the Wilhelmy plate method.

According to REACH Annex XI, 1. a test for the determination of the flash point of the substance is scientifically not necessary because the flash point refers to liquids (Reach R7.1.9). The substance is solid at ambient temperature; therefore a determination of the flash point is not required.

Up to the decomposition temperature (> 200°C) no self-ignition was observed. The test substance proved to be not highly flammable.

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. The test substance does not contain any chemical groups associated with explosive properties.

According to REACH Regulation (Annex VII, 7.13, column 2), the study on oxidising properties does not need to be done if the substance does not react exothermically with combustible material based on the chemical structure. The test substance 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 needs only to be done, if the stability is regarded as an essential property of the substance. The stability of the test substance in organic solvents is not regarded as critical.

According to REACH Regulation (Annex IX, 7.16, column 2), the study on the dissociation constant is scientifically not justified as the surface active substance is a zwitterion (inner salt; amphoteric surfactant) that has both acid and alkaline properties at environmental relevant pH values and which dissociates in water rapidly with e. g. Na+and Cl-acting as counterions.

According to the TGD R.7.1.18.4, viscosity is relevant only for liquids. Under standard conditions, the test substance is a solid. Therefore, according to REACH Regulation (Annex XI, 2.), a study on viscosity is technically not possible.