| Lithium 12-hydroxystearate | |
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Lithium 12-hydroxyoctadecanoate |
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| Identifiers | |
| CAS number | 7620-77-1 |
| PubChem | 111018 |
| ChemSpider | 99662 |
| Jmol-3D images | Image 1 |
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| Properties | |
| Molecular formula | C18H35LiO3 |
| Molar mass | 306.41 g mol−1 |
| Appearance | White powder |
| Melting point |
>200 °C |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) | |
| Infobox references | |
Lithium 12-hydroxystearate is a variety of lithium soap and an important component of many lubricating greases.
Contents |
Lithium 12-hydroxystearate exhibits high oxidation stability and a dropping point up to around 200 °C. Most greases used today in motor vehicles, aircraft, and heavy machinery contain lithium stearates, mainly lithium 12-hydroxystearate.[1] Greases can be made with the addition of several different metallic soaps. Some common additives include sodium, barium, lithium, and calcium. Lithium soap greases are preferred for their water resistance, and their oxidation and mechanical stability. Depending on the grease, they also have good performance at high or low temperatures, but not both high and low from the same formula. The others include some of these characteristics, but none have them all except lithium.
To produce lithium 12-hydroxystearate, lithium hydroxide hydrate and the fatty acid are combined in an aqueous medium. With vigorous stirring, dilute monohydrate lithium hydroxide is gradually added to a dispersion of the fatty acid in water heated to slightly below boiling.[2] Since these lithium soaps are difficult to filter, they are collected by spray drying. For applications, lithium 12-hydroxystearate is usually dispersed in synthetic oils such as silicone oil and ester oil. The synthetic oils are preferred for their greater stability and ability to perform at extreme temperatures.
The 12-hydroxystearic acid is prepared by the hydrogenation of castor oil.[3] After primary reaction of the saturation of most of the double bonds, dehydration and reduction of the hydroxyl group leads to the stearic acid. Hydrogenated castor oil results in a mixture of 12-hydroxystearic acid and stearic acid.