Graisses lubrifiantes

摘要

The mono-formic ester of dihydroxystearic acid is prepared by reacting oleic acid with hydrogen peroxide in the presence of formic acid. The ester may be hydrolysed, for example with alcoholic caustic potash or aqueous lithium hydroxide, and yields a complex formate-dihydroxystearate soap which may be employed as thickener in lubricating greases (see Group III). Dihydroxystearic acid, which is insoluble in ether, is obtained by acidifying the complex soap and extracting with ether.ALSO:A lubricating grease which maintains its structure when subjected to mechanical stress comprises a major proportion of lubricating oil thickened with a minor proportion of a complex soap obtained by neutralizing a mixture of dihydroxystearic acid and a C1-C5 monocarboxylic acid with a metal base. The lubricating oil may be mineral oil or a synthetic lubricating oil such as diester, a complex ester or a hydrocarbon polymer. Preferred lubricating oils are di-2-ethylhexyl sebacate and complex esters derived from dibasic acid, glycols and moonbasic asids. The C1-C5 monocarboxylic acid may be formic, acetic, propionic, butyric, valeric, furoic or acrylic acid, while the metal base may be a hydroxide of aluminium or of an alkali or alkaline earth such as lithium, sodium, potassium, calcium or barium. In addition to the complex soap, the grease may contain a simple soap of C10-C24 fatty acid, particularly lithium stearate. The grease may also contain other additives such as antioxidants, particularly amino compounds, and extreme pressure agents containing sulphur, halogen and/or phosphorus. The complex soap may be formed by adding the C1-C5 monocarboxylic acid to the molten dihydroxystearic acid, neutralizing the mixture with boiling aqueous metal hydroxide solution and drying at temperatures below the fusion point of the soap, and the complex soap then added to the lubricating oil. Alternatively, oleic acid may be condensed with a hydroxylating agent, such as hydrogen peroxide, in a solution of the C1-C5 monocarboxylic acid and the monoester or diester of dihydroxystearic acid with the C1-C5 acid thus formed hydrolyzed and neutralized with the metal base to produce the complex soap. Any unchanged oleic acid or any byproduct acids present will also be converted to soaps at the same time. If desired, the hydrolysis and neutralization may be carried out in the presence of a portion of the lubricating oil, if a nonsaponifiable lubricating oil is employed. In the examples, lubricating greases are prepared from a complex lithium formatelithium dihydroxystearate soap together with (1) di-2-ethylhexyl sebacate and phenyl alpha-naphthylamine or (2) mineral lubricating oil, lithium stearate and phenyl alpha-naphthylamine.