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Physical & Chemical properties

Endpoint summary

Administrative data

Description of key information

Additional information

Where testing has been conducted to generate data in order to complete physico-chemical endpoints, testing of lithium myristate (C14), at the lower end of the category, lithium 12-hydroxystearate (C18), as a hydroxylated member, and lithium behenate (C22), at the upper end of the category, was considered the most efficient approach. The data for the longest and shortest carbon chain lengths and for a hydroxylated substance in the middle of the category were generated to bracket the possible range of properties across the category and to show that substance properties are consistent across the range of carbon chain lengths. The testing of three substances at strategic points in the category is designed to ensure that the most conservative results are identified and, where appropriate, provide a classification which covers all of the substances in the category.

Appearance/physical state/colour

All of the substances in the lithium salts of monocarboxylic acids C14-C22 category are white solids at room temperature.

Lithium myristate is a white solid at ambient temperature. The data are taken from substance identification information in a GLP-compliant, guideline study available as an unpublished report (Harlan 2012).

Lithium 12 -hydroxystearate is a white solid at ambient temperature. The data are taken from substance identification information in a GLP-compliant, guideline study available as an unpublished report (Harlan 2012).

Lithium behenate is a white solid at ambient temperature. The data are taken from substance identification information in a GLP-compliant, guideline study available as an unpublished report (Harlan 2013).

Lithium myristate, the shortest carbon chain length substance in the category, lithium 12-hydroxysterate, with an intermediate carbon chain length, and lithium behenate, the longest carbon chain length substance in the category, are all white solids at room temperature. As these substances are all white solids at room temperature, it can be justifiably expected that the remaining substances in the category with intervening carbon chain lengths are white solids as well.

Melting point/freezing point

All of the substances in the lithium salts of monocarboxylic acids C14-C22 category have similar melting points, in the range of 166 to 231°C. All category members slowly decompose after melting.

The melting point of lithium myristate is 216 - 231°C and thereafter the substance slowly decomposes. The melting point of lithium myristate was determined in a GLP-compliant thermal analysis test, following OECD guideline 102 (Harlan 2012). This is supported by a melting point of lithium myristate of 223.6-224.2°C, taken from a peer-reviewed journal article, Shoeb (1999), citing a previous experimental study (Ralston 1948). No details are provided on the test methods or conditions and therefore the study has been assigned a Klimisch score of 4.

Shoeb (1999), states that the melting point of lithium palmitate is 224 -225°C. The melting point of lithium palmitate has been taken from a peer-reviewed journal article, citing a previous experimental study (Ralston 1948). No details are provided on the test methods or conditions and therefore the study has been assigned a Klimisch score of 4.

The melting point of lithium stearate is 220 - 221.5°C. There is no information available on the test methods or conditions but the data have been taken from a published regulatory review document (US EPA 2011). Although only a summary is available and there are limitations in design and/or reporting, the results are taken from a published regulatory document and are considered to be reliable and relevant for use. This is supported by Lide (2009), which states that the melting point of lithium stearate is ca. 220°C. No information on the primary source of the data or the methods used is available. However, this information is taken from a reliable peer reviewed handbook and can be considered reliable and relevant for use. This is also supported by a peer-reviewed journal article, Shoeb (1999), citing a previous experimental study (Ralston 1948), which states that the melting point of lithium stearate is 220.5 -221.5°C, though no details are provided on the test methods or conditions.

The melting point of lithium 12 -hydroxystearate is 200 - 216°C and thereafter the substance slowly decomposes. The melting point of lithium 12 -hydroxystearate was determined in a GLP-compliant thermal analysis test, following OECD guideline 102 (Harlan 2012).

The melting point of lithium behenate is 166°C and thereafter the substance slowly decomposes. The melting point of lithium behenate was determined in a GLP-compliant thermal analysis test, following OECD guideline 102 (Harlan 2013).

The melting point of lithium myristate, the shortest carbon chain length substance in the category, is 216-231°C. The melting points of lithium palmitate and lithium 12 –hydroxystearate, as substances with intermediate chain lengths, are 224 - 225°C and 200 - 216°C, respectively. The melting point of lithium behenate, the longest carbon chain length substance in the category, is 166°C. The study reports indicate that after melting, the substances slowly decompose.

The data indicate that melting points for lithium salts of fatty acids C14, C16 and C18 are all similar, at around 220°C, with the melting point of C22 being slightly lower, at around 166°C. Thus, it can be justifiably expected that the melting points of remaining substances in the category with intervening carbon chain lengths would fall within this range and can be read across from the available data. All of the substances in the lithium salts of monocarboxylic acids C14-C22 category are considered to have melting points in the range of 166 to 231°C.

Boiling point

All of the substances in the lithium salts of monocarboxylic acids C14-C22 category decompose on melting to give a solid residue. The boiling point test is therefore not technically feasible on these substances.

No determination of the boiling temperature was feasible for lithium myristate, lithium 12-hydroxystearate or lithium behenate as they were determined to decompose on melting to give a solid residue (Harlan 2012, Harlan 2013).

As the substances with the longest and shortest carbon chain length in the category, as well as an intermediary substance all behaved in the same manner it is considered justified to expect that the remaining substances in the category with intervening carbon chain lengths would also decompose to solid residues on melting.

Density

All of the substances in the lithium salts of monocarboxylic acids C14-C22 category have relative densities just greater than 1 at 20°C, with a range from 1.025 to 1.07.

The relative density of lithium myristate is 1.07 at 20°C. The relative density of lithium myristate was determined in a GLP-compliant pycnometer test following OECD guideline 109 (Harlan 2012).

The specific gravity of lithium stearate is 1.025. No information on the test method used is available in the publication (CIR 1982). However, the data forms part of a clinical assessment prepared by an expert panel and are taken from a peer reviewed article.

The relative density of lithium 12 -hydroxystearate is 1.04 at 20°C. The relative density of lithium 12 -hydroxystearate was determined in a GLP-compliant pycnometer test following OECD guideline 109 (Harlan 2012).

The relative density of lithium behenate is 1.04 at 20°C. The relative density of lithium behenate was determined in a GLP-compliant pycnometer test following OECD guideline 109 (Harlan 2013).

The relative densities of lithium myristate, lithium stearate, lithium 12-hydroxystearate and lithium behenate are all very similar, being just greater than 1. As all of these substances show similar densities, it can be justifiably expected that the densities of the remaining substances in the category would have similar relative density values as well. All of the substances in the lithium salts of monocarboxylic acids C14-C22 category are considered to have relative densities just greater than 1 at 20°C, with a range from 1.025 to 1.07.

Granulometry

Where the substances are manufactured and used in situ, the substances are not marketed or used in isolated solid or granular forms and so the particle size distribution test has been waived. Only lithium 12-hydroxystearate and fatty acids C16-C18 lithium salts are manufactured in an isolated form.

Proprietary data are available, which indicate that lithium 12-hydroxystearate has a D10 of 1.1 µm, a D50 of 4.9 µm and a D90 of 31.5 µm and fatty acids C16-C18 lithium salts have a D10 of 6.4 µm, a D50 of 33.8 µm and a D90 of 91.8 µm. The data are taken from proprietary analytical data (Baerlocher 2011).

For the two substances in the lithium salts of monocarboxylic acids C14-C22 category which are manufactured in an isolated form, proprietary analytical data are available. The data have not been read across to the other substances in the category, as these are all manufactured in situ in a base oil and are therefore not marketed isolated substances in granular form.

Vapour pressure

The vapour pressure could not be determined for any of the substances in the lithium salts of monocarboxylic acids C14-C22 category. The vapour pressure test is not technically feasible for these substances as the predicted vapour pressures were below the limit of detection of the test methods.

Standard test methods, according to OECD guideline 104, are able to measure vapour pressure from 10 E-10 Pa to 10 E+05 Pa. As the predicted vapour pressures for the substances in the lithium salts of monocarboxylic acids C14-C22 category are below 10 E-10 Pa, the vapour pressures tests were technically not feasible.

No determination of the vapour pressure is feasible for lithium myristate as the predicted vapour pressure is below the limit of detection of the test methods. Lithium myristate has a predicted vapour pressure of 2.29 E-12 Pa using the Modified Grain Method in EPISuite, MPBVP v1.43 (US EPA 2009).

No determination of the vapour pressure is feasible for lithium palmitate as the predicted vapour pressure is below the limit of detection of the test methods. Lithium palmitate has a predicted vapour pressure of 7.28 E-10 Pa using the Modified Grain Method in EPISuite, MPBVP v1.43 (US EPA 2009).

No determination of the vapour pressure is feasible for lithium stearate as the predicted vapour pressure is below the limit of detection of the test methods. Lithium stearate has a predicted vapour pressure of 1.35 E-10 Pa using the Modified Grain Method in EPISuite, MPBVP v1.43 (US EPA 2009).

No determination of the vapour pressure is feasible for lithium 12-hydroxystearate as the predicted vapour pressure is below the limit of detection of the test methods. Lithium 12-hydroxystearate has a predicted vapour pressure of 2.14 E-14 Pa using the Modified Grain Method in EPISuite, MPBVP v1.43 (US EPA 2009).

No determination of the vapour pressure is feasible for lithium behenate as the predicted vapour pressure is below the limit of detection of the test methods. Lithium behenate has a predicted vapour pressure of 7.89E-16 Pa using the Modified Grain Method in EPISuite, MPBVP v1.43 (US EPA 2009).

The vapour pressures of lithium myristate, lithium 12-hydroxystearate and lithium behenate were not determined as they all predicted to be below the limit of detection of the test methods. As the tests could not be conducted on the substances with the longest and shortest carbon chain length in the category, as well as an intermediary substance, it is considered justified to expect that the remaining substances in the category with intervening carbon chain lengths would have similarly low vapour pressures and therefore cannot be tested either. As the predicted vapour pressures for the substances in the lithium salts of monocarboxylic acids C14-C22 category are below 10 E-10 Pa, the vapour pressures tests were not conducted.

Water solubility

The water solubilities of the lithium salts of monocarboxylic acids C14-C22 category could not be determined. The water solubility for lithium behenate (C22) was determined to be ≤0.000046 g/L. The remaining substances in the category, those with a carbon chain length of less than C22, have surface active properties. As the substances formed stable dispersions in water rather than being truly soluble, the water solubility could not be determined.

The water solubility of lithium myristate and lithium 12-hydroxystearate could not be analytically determined because, after static equilibration, centrifugation and filtration, excess undissolved test item remained in the dispersion. The water solubility studies on lithium myristate and lithium 12-hydroxystearate were tested in GLP-compliant preliminary studies (Harlan 2012). The tests demonstrated that lithium myristate and lithium 12-hydroxystearate have surface active properties.

The water solubility of lithium behenate is ≤0.000046 g/L at 20°C. The water solubility of lithium behenate was determined in a GLP-compliant test following EU method A6 (Harlan 2013).

Data are available from a range of published sources which have indicated water solubility values for substances in the lithium salts of monocarboxylic acids C14-C22 category. A published study following a non-standard method (Jacobson 1916) gave a water solubility of 0.027 g/100 g at 16.3°C for lithium myristate, of 0.1 g/L at 16.3°C for lithium palmitate and of 0.009 g/100 g at 16.3°C for lithium stearate. Water solubility values for lithium stearate of 0.098 g/L (US EPA 2011) and 0.1 g/L at 18°C (Lagerkvist 2002) were taken from published regulatory documents, though no information is available on the test methods or conditions. The study summaries do not mention any methods for addressing the surface activity of the substances or problems with conducting the testing. As the lithium salts up to C22 are shown to be surface active, these published water solubility values are not considered to be reliable.

It is expected that the water solubility of the substances in the category decrease with increasing carbon chain length. However, the water solubility could not be experimentally determined for substances with a carbon chain length of less than C22. The water solubility of lithium behenate, the longest carbon chain length substance, was determined to be ≤0.000046 g/L. The water solubilities of lithium myristate, the shortest carbon chain length substance, and lithium 12-hydroxystearate, an intermediate carbon chain length substance, could not be analytically determined because the undissolved test item remained in dispersion, even after filtration and centrifugation. All of the substances in the lithium salts of monocarboxylic acids C14-C22 category, other than lithium behenate, are considered to have surface active properties and therefore form stable dispersions rather than being truly soluble.

Partition Coefficient

The partition coefficient could not be determined for any of the substances in the lithium salts of monocarboxylic acids C14-C22 category. The partition coefficient tests are not technically feasible on these substances.

No determination was carried out using the shake-flask method or HPLC estimation method as lithium myristate and lithium 12-hydroxystearate had demonstrated significant surface active properties and the procedures are not suitable for surface active substances.

No determination was carried out using the shake-flask method or HPLC estimation method as lithium behenate was insufficiently soluble in n-octanol and water which prevented the use of the shake-flask method and the HPLC method is not suitable for salts of organic acids.

The partition coefficients were estimated by QSAR but the results are considered not to be relevant to the substances themselves. As the lithium salts of monocarboxylic acids C14-C22 are ionisable salts, the partition coefficient can vary greatly depending on pH and the pKa of the substance. In order to compare partition coefficient values of different, ionizable compounds on a relative basis, partition coefficient values are sometimes reported as "corrected for ionization", indicating that the value represents the partition coefficient at a pH where a compound exists primarily in the non-ionized form. However, KOWWIN (KOWWIN v1.67 in EPISuite v4.00, US EPA 2009) considers lithium salts of monocarboxylic acids C14-C22 to be “ion pairs” and as such only provides estimates for the ionised fatty acids rather than the salts. The partition coefficient values for the salts themselves therefore could not be determined.

The lithium salts of fatty acids in this category are typically not synthesized as the “pure” compounds and seldom exist except in the presence of the oil matrix. High temperature stability indicates that the grease thickener structure is robust and resistant to diffusion out of the oil. Dissolution of grease thickeners from grease into water is very unlikely as the thickeners are poorly water soluble and the thickeners are embedded in the hydrophobic grease matrix and thus less likely to leach out. Thus the partition coefficient of the substances is not expected to be relevant.

The partition coefficients of lithium myristate, lithium 12-hydroxystearate and lithium behenate could not be determined as they all are either surface active or have insufficient solubility in octanol. As the tests could not be conducted on the substances with the longest and shortest carbon chain length in the category, as well as an intermediary substance, it is considered justified to expect that the remaining substances in the category with intervening carbon chain lengths would behave in the same manner and therefore cannot be tested for partition coefficient either.

Surface tension

Substances in the lithium salts of monocarboxylic acids C14-C22 category have increasing surface tension with increasing carbon number. As the cut-off for being considered surface active is 60 mN/m and lithium behenate only slightly exceeds this, category members with carbon chain lengths of less than 22 are considered to have surface active properties.

The surface tension of a saturated solution of 1.02 to 1.03 g/L lithium myristate is 34.0 mN/m at 21.5°C. The surface tension of lithium myristate was conducted in a GLP-compliant ring balance test following OECD guideline 115 (Harlan 2012). The study deviated from the guideline because the method used did not require re-calibration and the test item formed stable dispersions from which the undissolved test item could not be removed. These deviations were not considered to have affected the integrity of the study. Lithium myristate has a surface tension below 60 mN/m and is therefore regarded as being surface active. This is consistent with the observed characteristics of lithium myristate in water and its structure, which is representative of the "soap" surfactant class.

The surface tension of a saturated solution of 1.00 to 1.01 g/L lithium 12 -hydroxystearate is 51.9 to 52.0 mN/m at 21.5°C. The surface tension of lithium 12 -hydroxystearate was conducted in a GLP-compliant ring balance test following OECD guideline 115 (Harlan 2012). The study deviated from the guideline because the method used did not require re-calibration and the test item formed stable dispersions from which the undissolved test item could not be removed. These deviations were not considered to have affected the integrity of the study. Lithium 12 -hydroxystearate has a surface tension below 60 mN/m and is therefore regarded as being surface active. This is consistent with the observed characteristics of lithium 12 -hydroxystearate in water and its structure, which is representative of the "soap" surfactant class.

The surface tension of a saturated solution of 1.00 to 1.07 g/L lithium behenate is 61.8 to 65.9 mN/m at 21.0°C. The surface tension of lithium behenate was conducted in a GLP-compliant ring balance test following OECD guideline 115 (Harlan 2013). The study deviated from the guideline because the ring apparatus had a smaller diameter than recommended in the guideline and excess, undissolved lithium behenate formed a stable dispersion in the water. These deviations were not considered to have affected the integrity of the study. Lithium behenate has a surface tension above 60 mN/m and is therefore regarded as not surface active.

The surface tension of lithium myristate is 34.0 mN/m at 21.5°C and a concentration of 1.02 to 1.03 g/L. The surface tension of lithium 12-hydroxystearate is 51.9 to 52.0 mN/m at 21.5°C and a concentration of 1.00 to 1.01 g/L. The surface tension of lithium behenate is 61.8-65.9 mN/m at 21.5°C and a concentration of 1.00 to 1.07 g/L. As the boundary for surface activity properties is 60 mN/m, lithium myristate and lithium 12 -hydroxystearate are considered to be surface active, but lithium behenate is considered not to be surface active.

All of the substances in the category have a structure which is representative of the "soap" surfactant class (the lithium ion being the hydrophilic head and the fatty acid being the hydrophobic tail), however as the surface tension of the substances increases with increasing carbon chain length, only the shorter carbon chain length substances (<C22) meet the criteria to be considered surface active.

Auto-flammability

All of the substances in the lithium salts of monocarboxylic acids C14-C22 category have self-ignition temperatures above their melting points. Therefore none of the substances in the category meet the criteria for classification as a self-heating substance.

Lithium myristate was determined not to have a relative self-ignition temperature below its melting point (i.e. >231°C). The relative self-ignition temperature of lithium myristate was tested in a GLP-compliant study following EC 440/2008 A16 method (Harlan 2013).

Lithium 12 -hydroxystearate was determined not to have a relative self-ignition temperature below its melting point (i.e. >216°C). The relative self-ignition temperature of lithium 12 -hydroxystearate was tested in a GLP-compliant study following EC 440/2008 A16 method (Harlan 2013).

Lithium behenate was determined not to have a relative self-ignition temperature below its melting point (i.e. >167°C). The relative self-ignition temperature of lithium behenate was tested in a GLP-compliant study following EC 440/2008 A16 method (Harlan 2013).

The self-ignition temperatures of lithium myristate, lithium 12-hydroxystearate and lithium behenate are all above their melting points. As the self-ignition temperature of the substances with the longest and shortest carbon chain lengths in the category, as well as one with an intermediary chain length, are above their respective melting points, it is considered justified to expect that the remaining substances in the category with intervening carbon chain lengths would also have self-ignition temperatures above their respective melting points. Therefore none of the substances in the category meet the criteria for classification as a self-heating substance.

Flammability

None of the substances in the lithium salts of monocarboxylic acids C14-C22 category are considered to be highly flammable. Therefore none of the substances in the category meet the criteria for classification as flammable solids.

Lithium myristate has been determined to be not highly flammable as it failed to ignite in the preliminary screening test. The flammability of lithium myristate was tested in a GLP-compliant test following the method EC440/2008 A10 (Harlan 2013).

Lithium 12 -hydroxystearate has been determined to be not highly flammable as it failed to ignite in the preliminary screening test. The flammability of lithium 12 -hydroxystearate was tested in a GLP-compliant test following the method EC440/2008 A10 (Harlan 2013).

Lithium behenate has been determined to be not highly flammable as it failed to ignite in the preliminary screening test. The flammability of lithium behenate was tested in a GLP-compliant test following the method EC440/2008 A10 (Harlan 2013).

Lithium myristate, lithium 12-hydroxystearate and lithium behenate are not considered to be flammable as they all failed to ignite in the preliminary screening test. As the substances with the longest and shortest carbon chain lengths in the category, as well an intermediary substance, are not highly flammable, it is considered justified to expect that the remaining substances in the category with intervening carbon chain lengths would not be highly flammable either. None of the substances in the lithium salts of monocarboxylic acids C14-C22 category are considered to be highly flammable. Therefore none of the substances in the category meet the criteria for classification as flammable solids.

Experience in manufacture and handling shows that the substances in the lithium salts of monocarboxylic acids C14-C22 category do not ignite spontaneously on coming into contact with air at normal temperatures and are stable at room temperature for prolonged periods of time (days). Experience has also shown that the substances do not react with water and therefore they do not meet the criteria for classification as pyrophoric substances or substances which in contact with water emit flammable gases.

Dissociation constant

The dissociation constant is an annex IX endpoint, and is therefore only required for lithium 12-hydroxystearate, castor oil hydrogenated lithium salts and fatty acids C16-C18 lithium salts. No data are available on the dissociation constants for these three substances, so the dissociation constants have been read across from sodium palmitate (Kanicky et al 2000) and potassium stearate (Kanicky and Shah 2002).

Kanicky et al. (2000) titrated sodium palmitate with sodium hydroxide and calculated the mean pKa from the pH at half the neutralisation volume for each of the five replicates. Kanicky and Shah (2002) titrated potassium stearate with hydrochloric acid and calculated the mean pKa from the pH at half the neutralisation volume for each of the five replicates. The studies are non-GLP, non-guideline experiments, available in peer-reviewed published journal articles. The experiments follow sound scientific principles and are considered adequate for assessment.

Lithium, sodium and potassium are all low-molecular weight metals and the fatty acid salts of these metals are expected to have very similar physico-chemical properties. The substances vary predominantly by the composition of the metal cation with the majority of the molecular weight of each substance being comprised of monocarboxylic acids.

Fatty acid metal salts are expected to dissociate into free metal cation and fatty acid anions in water. The fatty acid would then be expected to achieve equilibrium with respect to the H+ ions in the water (depending on the pKa of the fatty acid) and at neutral pH there would be ionised fatty acids, unionised fatty acids, and free metal ions. As the dissociation constants of metal salts of fatty acids are expected to be determined by the equilibrium of the fatty acids with respect to the hydrogen ions in the water, read across between different metal salts of the same fatty acids is considered to be justified.

The measured dissociation constant for sodium palmitate of 8.8 (Kanicky et al. 2000) and for potassium stearate of 10.15 (Kanicky and Shah 2002) are both relatively high and thus the fatty acid would be expected to be unionised (protonated) at environmental pH. This would suggest that in solution the fatty acid and metal ions would be dissociated (although these substances do not tend to become truly dissolved) and would suggest that stearic acid would be almost entirely protonated at pH < 8. As such, the pKa of the analogous fatty acid substances are all expected to be above 8, with ionised fatty acids expected to become protonated at neutral pH.

Other physico-chemical endpoints

As the lithium salts of monocarboxylic acids C14-C22 are solids, the viscosity and flash point endpoints are not required. Based on the structure of the substances in this category, the explosiveness and oxidising properties studies have not been conducted as there are no structural alerts that would indicate explosive or oxidising properties. The stability in organic solvents and identity of relevant degradation products study has not been conducted as it is not considered to be a critical endpoint. Where the substances are manufactured and used in situ in a base oil, the substances are not marketed or used in solid or granular forms and so the particle size distribution test has been waived. For the two substances manufactured and used in an isolated form, proprietary data on particle size distribution have been included.

Classification and labelling

None of the substances in the lithium salts of monocarboxylic acids C14-C22 category are classified for physico-chemical hazards under the CLP or the DSD. Based on the structure of the substances, they do not meet the criteria for oxidising or explosive properties and based on experimental data, the substances do not meet the criteria for flammable solids or self-heating substances.