Linoleic acid
- ( cis, cis) - octadeca -9 ,12- dienoic acid
- ( Z, Z) -9,12 - octadecadienoic acid
- 18:2 ( ω -6) (lipid Name )
Colorless to yellowish liquid
Liquid
0.9 g · cm -3 ( 18 ° C)
-5 ° C
230 ° C (21 hPa)
4.77 (25 ° C)
- Very poor in water ( 139 mg · l-1 at 20 ° C)
- Well in many organic solvents
1.466 at 20 ° C.
Template: Infobox chemical / molecular formula search available
Linoleic acid, scientifically (cis, cis) octadeca -9 ,12- dienoic acid is a diunsaturated fatty acid having 18 carbon atoms ( 18:2 ). It is one based on the location of their second double bond to the group of omega-6 fatty acids and must be distinguished from linolenic acid.
The name derives from the Latin linum linoleic acid (Greek linon ) for linseed ( flax) and oleum "oil" from.
Occurrence
Linoleic acid is an ester chemically bound in many triglycerides in front of which are major part of the natural fatty oils. Grape seed oil with 58-78 % oil and safflower oil ( safflower oil ) with 55-81 have the highest linoleic acid content of all vegetable oils. Also in hemp oil (about 50 % ), soy oil ( 49-57 %), cottonseed oil ( 45-58 % ), wheat germ oil ( 40-55 %), corn oil ( 34-62 % ), sunflower oil ( 20-75 %) and rapeseed oil (18-30 %) found high proportions; the faces of olive oil with only 3-20 % linoleic acid.
Production and representation
The fatty acids can be obtained by alkaline hydrolysis of the triglycerides by the corresponding fats or oils are boiled with alkalis. Since the natural fats and oils always contain many different fatty acids, joins usually a separation by distillation of the resulting mixture at.
Commercially prepared linoleic acid has a stake of up to 67%, in addition, it contains a mixture of other saturated and unsaturated fatty acids, especially oleic acid.
Properties
Pure linoleic acid is a colorless, oily and almost odorless liquid. It is sensitive to oxidation and aging in the air under yellow coloring, which is due to the formation of hydroperoxides. The molar mass is 280.45 g mol -1, and the density of 0.9 g · cm - 3 having a melting point of -5 ° C and a boiling point of 230 ° C. The fatty acid is very poorly soluble in water, but well soluble in many organic solvents. Chemically, it belongs to the hydrophobic carboxylic acids, striking, however, is their highly divergent from the other homologs pKa value of 7.9 (typically 4.75 to 4.95 ).
Biological Significance
Linoleic acid, as well as α -linolenic acid, an essential nutrient, and therefore has to be supplied in sufficient quantity in the diet. Be of linoleic acid in the body via the intermediate γ -linolenic acid ( GLA) in the important inflammatory processes dihomogammalinolenic ( anti-inflammatory) and arachidonic acid ( pro-inflammatory ) synthesized.
Linoleic acid is a regular part of the human skin, especially the epidermis. Responsible for the regulation of water balance decisively important epidermal barrier - a structure represented by the stratum corneum - consists of ceramides, free fatty acids and phospholipids. Ceramides have a special meaning for water regulation. Quantitatively significant ceramide is ceramide 1, whose main component is linoleic acid. Linoleic acid is applied externally in a position
- Counteract skin irritation from the outside ( irritant contact dermatitis),
- Chronic photodamage of the skin to counteract
- Occurring in the context of photodamaged skin age spots regress
- To reduce the size of blackheads.
However, the effect due to the molecular size is found in only already damaged skin.
Linoleic acid is used without predetermined maximum concentration in cosmetics.
Proof
The detection and determination of content of linoleic acid is carried out typically by gas chromatography of the methyl ester; supplement can be a separation of the unsaturated isomers with silver nitrate thin layer chromatography.
Technical use
Acylglycerols of linoleic acid and linolenic acid are (including paints) used as an additive to varnish and other drying oils for coatings.