Lithium 12-hydroxystearate
Encyclopedia
Lithium 12-hydroxystearate is a variety of lithium soap and an important component of many lubricating greases
Grease (lubricant)
The term grease is used to describe semisolid lubricants. Although the word grease is also used to describe rendered fat of animals, in the context of lubrication, grease typically applies to a material consisting of a soap emulsified with mineral or vegetable oil...

.

Use

Lithium 12-hydroxystearate exhibits high oxidation stability and a dropping point
Dropping point
The dropping point of a soap-thickened lubricating grease is the temperature at which it passes from a semi-solid to a liquid state under specific test conditions...

 up to around 200 °C. Most greases used today in motor vehicles, aircraft, and heavy machinery contain lithium stearate
Lithium stearate
Lithium stearate is a chemical compound with the formula LiO2C16CH3. It is formally classified as a soap . Lithium stearate is a white soft solid, prepared by the reaction of lithium hydroxide and steric acid....

s, mainly lithium 12-hydroxystearate. Greases can be made with the addition of several different metallic soaps. Some common additives include sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

, barium
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...

, lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...

, and calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

. 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.

Production

To produce lithium 12-hydroxystearate, lithium hydroxide
Lithium hydroxide
Lithium hydroxide is an inorganic compound with the formula LiOH. It is a white hygroscopic crystalline material. It is soluble in water and slightly soluble in ethanol...

 hydrate
Hydrate
Hydrate is a term used in inorganic chemistry and organic chemistry to indicate that a substance contains water. The chemical state of the water varies widely between hydrates, some of which were so labeled before their chemical structure was understood....

 and the fatty acid
Fatty acid
In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...

 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. 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
Silicone oil
A silicone oil is any polymerized siloxanes with organic side chains. They are formed of alternating silicon-oxygen atoms or siloxane, rather than carbon atoms . Other species attach to the tetravalent silicon atoms, not to the divalent oxygen atoms which are fully committed to forming the...

 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
Hydrogenation
Hydrogenation, to treat with hydrogen, also a form of chemical reduction, is a chemical reaction between molecular hydrogen and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically...

 of castor oil
Castor oil
Castor oil is a vegetable oil obtained from the castor bean . Castor oil is a colorless to very pale yellow liquid with mild or no odor or taste. Its boiling point is and its density is 961 kg/m3...

. After primary reaction of the saturation
Saturation
Saturation or saturated may refer to:- Meteorology :* Dew point, which is a temperature that occurs when atmospheric humidity reaches 100% and the air is saturated with moisture- Physics :...

 of most of the double bond
Double bond
A double bond in chemistry is a chemical bond between two chemical elements involving four bonding electrons instead of the usual two. The most common double bond, that between two carbon atoms, can be found in alkenes. Many types of double bonds between two different elements exist, for example in...

s, dehydration
Dehydration reaction
In chemistry and the biological sciences, a dehydration reaction is usually defined as a chemical reaction that involves the loss of water from the reacting molecule. Dehydration reactions are a subset of elimination reactions...

 and reduction of the hydroxyl group leads to the stearic acid
Stearic acid
Stearic acid is the saturated fatty acid with an 18 carbon chain and has the IUPAC name octadecanoic acid. It is a waxy solid, and its chemical formula is CH316CO2H. Its name comes from the Greek word στέαρ "stéatos", which means tallow. The salts and esters of stearic acid are called stearates...

. Hydrogenated castor oil results in a mixture of 12-hydroxystearic acid and stearic acid.
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