Lithium isooctadecanoate

Endpoint summary

Additional information

Appearance/physical state/colour 

 

Lithium isooctadecanoate is a pale yellow solid at ambient temperature. The data are taken from substance identification information in a GLP-compliant, guideline study available as an unpublished report (Envigo 2017).

 

Melting point/freezing point 

 

The melting point of lithium isooctadecanoate is 193-205°C. Lithium isooctadecanoate begins to decompose at 185°C. The melting point was determined in a GLP-compliant thermal analysis test, using differential scanning calorimetry and a capillary method using visual evaluation following OECD guideline 102 (Envigo 2017).

 

Boiling point 

 

No experimental determination of the boiling temperature was possible for lithium isooctadecanoate as detailed in Method A2 Boiling Temperature of Commission Regulation (EC) No 440/2008 of 30 May 2008, and Method 103 of the OECD Guidelines for Testing of Chemicals, 27 July 1995, because the test item had been demonstrated to decompose prior to melting.

 

Density 

 

The density of lithium isooctadecanoate has been determined to be 959 kg/m3 at 20.0 ± 0.5°C (relative density value 0.959). The density of the test item was determined in a GLP-compliant gas comparison pycnometer (for solids) test following OECD guideline 109 (Envigo 2017).

 

Granulometry 

 

The particle size distribution test has been waived because the substance is not manufactured or used in a non-solid or granular form. The main use of the substance is as a viscosity regulator for grease lubricants, a use for which it is manufactured, marketed and used in base oil.

 

Vapour pressure 

 

The vapour pressure of lithium isooctadecanoate was not determined because the standard test methods, according to OECD guideline 104, are able to measure vapour pressure from 10 E-10 Pa to 10 E+05 Pa, and the predicted vapour pressure for lithium isooctadecanoate is 2.25 E-10 Pa at 25°C which is below 10 E-10 Pa (US EPA 2009). However, testing is currently ongoing to confirm this conclusion.

 

Water solubility 

 

No determination of water solubility was feasible for lithium isooctadecanoate. Lithium isooctadecanoate, representative of the chemical class of lithium soaps, showed significant surface-active properties in an aqueous environment. When attempting to generate saturated solutions, a colloidal suspension (i.e. containing micelles < 0.2 µm) was formed. As this dispersed, excess, undissolved material could not be satisfactorily removed by either centrifugation or filtration techniques, it was not possible to isolate a genuine saturated aqueous solution of test item suitable for analysis and quantification. The water solubility test for lithium isooctadecanoate was conducted in a GLP-compliant study (Envigo 2017) following OECD guideline 105. Further testing is currently ongoing to confirm this conclusion.

  

Partition Coefficient 

 

No determination was carried out using Method A8 Partition Coefficient of Commission Regulation (EC) No 440/2008 of 30 May 2008 and Method 107 of the OECD Guidelines for Testing of Chemicals, 27 July 1995, as the test item demonstrated significant surface-active properties. The procedure is not suitable for surface-active substances. Therefore, the partition coefficient was estimated by QSAR.

  

The Environmental and Health Risk Assessment and Management (Erasm) taskforce has reviewed the common experimental (OECD 107 shake flask method, OECD 123 slow stirring method, OECD 117 HPLC method, and n-octanol/water solubility ratio method) and predictive methods (QSARs) for determination of partition coefficient of surfactants. The results of the investigations were published in Hodges et al. (2019) and all methods were identified as having limitations for determining accurate partition coefficient values for surfactants. The OECD 123 slow stirring method is considered to be preferred for surfactants (Hodges et al. 2019), though it requires a sensitive analytical method to analyse the test item in the water phase and the OECD 123 guideline clearly states under "applicability of the test" that the slow stirring method applies to pure substances which do not display significant interfacial activity. The HPLC method, which uses the retention time of a material to provide an indication of the partition coefficient, is not applicable as there is lack of reference surfactants with accurately determined log Kow values (Hodges et al. 2019) and, furthermore, the HPLC method is not suitable for salts of organic acids. Partition coefficient calculation based on the measured n-octanol and water solubilities is not always relevant or robust as the solubility of surfactants in water can be difficult to experimentally determine and may not be properly defined. Hodges et al. (2019) concluded that “there is little correlation between log Kow values generated using the slow-stirring and solubility ratio methods… [and the] available data suggest that the solubility ratio approach may underestimate the log Kow values compared to the slow stir method”. Hodges et al. (2019) concluded that “the solubility ratio method is not recommended as a robust or accurate method for the determination of log Kow values for the four classes of surfactants [non-ionic, anionic, cationic and amphoteric] assessed in this study”.

 

The octanol/water partition coefficient, Kow, is defined as the ratio of the equilibrium concentrations of a dissolved substance in each of the phases in a two-phase system consisting of octanol and water. It is a key parameter in studies of the environmental fate of organic substances, indicating the potential for bioaccumulation and soil absorption. It does not pertain to the substance and, instead of the determination of a Kow value, the environmental fate and distribution of the dissociation products of the substance in water are better assessed according to the dissociation products in water as follows:

 

(i) the mechanisms for partitioning of Li+ in environmental media, including the adsorption and/or absorption by organic matter and living cells, are understood to be different from those traditionally attributed to carbon-based molecules and, thus, octanol/water partitioning has little relevance to ionic lithium. In order to measure an octanol/water partition coefficient, it is necessary to determine the concentration in each phase (as in OECD method 107), or to conduct an HPLC assay (as in OECD method 117). However, lithium is a metallic element that exists only in an ionic form in solution. The solubility of lithium cations in water is high and can safely be expected to be low in organic solvents such as octanol. Because of the unlikely partitioning of lithium cations into the octanol phase, it is not appropriate to determine the partition coefficient by direct quantification of lithium in both phases. Similarly, any aqueous HPLC mobile phase will cause dissociation of inorganic lithium compounds, and thus not allow the determination of a Kow by this method.

 

(ii) regarding the partitioning behaviour of fatty acid constituent (as reported in the registration dossier): isooctadecanoic acid has a log Kow of 7.87 (KOWWIN).

 

Furthermore, the main use of the substance is as a viscosity regulator for grease lubricants, a use for which it is manufactured, marketed and used in base oil. Lithium isooctadecanoate seldom exists except in the presence of the oil matrix and high temperature stability indicates that the grease thickener structure is robust and resistant to diffusion out of the oil. Dissolution of the grease thickener from grease into water is very unlikely as the thickener is poorly water soluble and the thickener is embedded in the hydrophobic grease matrix and thus less likely to leach out. Thus, the partition coefficient of the substance is not expected to be relevant. 

 

 Surface tension 

 

The surface tension of duplicate 90% saturated aqueous solutions of lithium isooctadecanoate has been determined to be 39.5 mN/m at 20.0 ± 0.5°C. Since the substance showed a surface tension less than 60 mN/m, it was considered to be surface active. The surface tension of the test material was determined in a GLP-compliant ring balance test following OECD guideline 115 (Envigo 2017).

 

Auto-flammability 

 

Lithium isooctadecanoate was determined not to have a relative self-ignition temperature below 400°C. The relative self-ignition temperature of the test item was determined in a GLP-compliant study following EC 440/2008 A16 method (Envigo 2017).

 

Flammability 

 

Lithium isooctadecanoate was determined to be not highly flammable as it failed to propagate combustion along 200 mm within 4 minutes. The flammability of the test item was determined in a GLP-compliant test following the method EC440/2008 A10 (Envigo 2017).

  

Experience in manufacture and handling shows that lithium isooctadecanoate does not ignite spontaneously on coming into contact with air at normal temperatures and is stable at room temperature for prolonged periods of time (days). Experience has also shown that the substance does not react with water. It, therefore, does not meet the criteria for classification as a pyrophoric substance or a substance which in contact with water emits flammable gases.

 

Other physico-chemical endpoints 

 

As lithium isooctadecanoate is a solid, the flash point endpoint is not required. Based on the structure of the substance, the explosiveness and oxidising properties studies have not been conducted as there are no structural alerts that would indicate explosive or oxidising properties. As the substance is manufactured and usedin situin a base oil and not marketed or used in isolated forms, the particle size distribution test has been waived.

 

Classification and labelling

 

The substance is not classified for physico-chemical hazards. Based on the structure of the substance, it does not meet the criteria for oxidising or explosive properties and based on experimental data, the substance does not meet the criteria for flammable solids. Experience in manufacture and handling shows that the substance is not a self-heating solid.