Oleic acid

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Structural formula
Structure of oleic acid
Structural formula with the numbering of selected carbon atoms
General
Surname Oleic acid
other names
  • (9 Z ) -Octadec-9-enoic acid ( IUPAC )
  • cis -9-octadecenoic acid
  • Oleic acid
  • 18: 1 (ω − 9) ( lipid name )
  • OLEIC ACID ( INCI )
Molecular formula C 18 H 34 O 2
Brief description

colorless to yellowish liquid with a fatty odor

External identifiers / databases
CAS number 112-80-1
EC number 204-007-1
ECHA InfoCard 100.003.643
PubChem 445639
ChemSpider 393217
DrugBank DB04224
Wikidata Q207688
properties
Molar mass 282.46 g mol −1
Physical state

liquid

density

0.89 g cm −3

Melting point

16 ° C

boiling point

360 ° C

Vapor pressure

1.9 · 10 −6 Pa (298 K)

solubility

almost insoluble in water (12 mg l −1 , 25 ° C), soluble in methanol

Refractive index

1.4582 (20 ° C)

safety instructions
GHS labeling of hazardous substances
no GHS pictograms
H and P phrases H: no H-phrases
P: no P-phrases
MAK

not yet determined

Toxicological data
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Oleic acid , also called oleic acid, is the most important representative of the monounsaturated fatty acids (18: 1). Its systematic name is ( Z ) -9-octadecenoic acid and it is an omega-9 fatty acid due to the location of its double bond . A naturally occurring isomer of oleic acid is petroselinic acid , the trans isomer is known as elaidic acid . The salts and esters of oleic acid are called oleates .

Example of a triglyceride that is rich in unsaturated fatty acid residues. The fatty acid residue marked blue is monounsaturated and is derived from oleic acid, the linoleic acid residue marked green is twofold, the linolenic acid residue marked red is threefold unsaturated . The carbon-carbon double bonds are consistently cis -configured. The triple acylated glycerine can be seen in black in the center . Oils contain a higher proportion of essential fatty acid residues (= unsaturated fatty acid residues) than fats.

Occurrence

Oleic acid occurs chemically bound in triglycerides in almost all natural (vegetable and animal) oils and fats. A particularly high proportion of such esterified oleic acid have z. B. Olive oil (70-75%), peanut oil  (50-70%), rapeseed oil (HEAR varieties 12-24%, LEAR varieties 50-65%), avocado oil  (44-76%), goose fat  (41-72 %), Palm oil  (37–42%), lard  (36–52%), sesame oil  (35–46%), mutton tallow  (31–56%), beef tallow  (26–45%), sunflower oil   (14–65%) and especially so-called high oleic sunflower oil from specially cultivated varieties with 75-93% oleic acid.

Contrary to popular belief, these natural fats and oils do not contain free oleic acid, but their glycerol esters .

Extraction and presentation

The fatty acids can be obtained from the corresponding triacylglycerides by alkaline saponification by boiling the corresponding fats or oils with bases . The saponification itself initially supplies their salts. The free fatty acids are obtained by neutralization with (mineral) acids. Since natural fats and oils always contain many different fatty acids, the resulting mixture is usually separated by distillation .

Commercially, oleic acid is obtained from tallow through hydrolysis and subsequent crystallization . This process can produce concentrations of around 70%, known as olein. In addition to oleic acid, palmitoleic acid , linoleic acid and other unsaturated and saturated fatty acids can be contained in this mixture . By hydrolyzing very oleic vegetable oils such as olive oil, Euphorbia lathyris or high oleic sunflowers, purities of more than 90% can be obtained.

properties

Physical Properties

Pure oleic acid is a colorless, oily and almost odorless liquid. The molar mass is 282.46 g · mol −1 and the density 0.89 g · cm −3. It has a melting point of 17 ° C and a boiling point of 360 ° C. The fatty acid is insoluble in water but soluble in methanol . The flash point is 189 ° C, the ignition temperature 250 ° C.

Chemical properties

Compared to polyunsaturated fatty acids (e.g. linolenic acid ), oleic acid is only slightly sensitive to oxidation. It slowly oxidizes in air, turning yellow, which is due to the formation of decay products. The main point of attack for the oxidation is the CC double bond. It is particularly promoted by light, heat or dissolved metal ions and proceeds mainly via radical reaction mechanisms. An important intermediate step in the oxidation is the formation of hydroperoxides (–OOH) when the C = C double bond is broken. The functional group (–OOH) itself also forms radicals and thus promotes an oxidative chain reaction. Further, hydroperoxides to ketones decompose and, if it comes to a split of simple C-C bond, even to aldehydes or carboxylic acids .

Oleic acid, and especially its salts, are amphiphilic , that is, they contain both a polar, hydrophilic part (the carboxy group ) and a non-polar, lipophilic part (the hydrocarbon chain).

nomenclature

Oleic acid with key positions marked in blue and green

According to IUPAC, oleic acid is called “( Z ) -9-octadecenoic acid”; Here, the carbon atom of the obtained carboxyl group which Lokantenziffer 1 (left structure image blue 1), the double bond is at position 9 (Blue 9) and the molecule has ( Z ) -configuration (see cis - trans isomerism ). In addition, unsaturated fatty acids relevant for food are given a lipid name, here 18: 1 (ω − 9) ; this is derived from the number of carbon atoms and double bonds (18: 1) and also indicates the position of the double bond, counted from the ω end of the molecule. In this case, the carbon atom opposite the carboxy group is assigned the position 1 or ω (green lettering); the position of the double bond happens to be identical to the IUPAC designation (green 9).

proof

The detection and determination of the content of oleic acid as well as other fatty acids in fats is usually carried out by gas chromatography of the methyl ester ; In addition, the unsaturated isomers can be separated using silver nitrate thin-layer chromatography. A second, unspecific detection method is the bromine water sample . The result is a disappearance of the brown color.

use

Oleic acid is used as a component of mixtures with other fatty acids in variable proportions, primarily for the manufacture of soaps and metal soaps as well as for surfactant production. Use as a lubricant in the textile industry has been proven.

Individual evidence

  1. ↑ entry to oleic acid in the CosIng database of the European Commission, accessed on 11 March 2020th
  2. ↑ a b c d e f g h i j Entry on oleic acid in the GESTIS substance database of the IFA , accessed on December 20, 2019(JavaScript required) .
  3. ↑ a b c d e f g h i j Entry on oleic acid. In: Römpp Online . Georg Thieme Verlag, accessed on May 16, 2012.
  4. ↑ CD Cappa, ER Lovejoy, AR Ravishankara: Evaporation Rates and Vapor Pressures of the Even-Numbered C 8 −C 18 Monocarboxylic Acids. In: J. Phys. Chem. A 112, 2008, pp. 3959-3964, doi : 10.1021 / jp710586m .
  5. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Physical Constants of Organic Compounds, pp. 3-406.
  6. ^ Siegfried Hauptmann : Organic Chemistry , 2nd revised edition, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig, 1985, pp. 653–654, ISBN 3-342-00280-8 .
  7. ↑ Entry on rapeseed oil. In: Römpp Online . Georg Thieme Verlag, accessed on May 16, 2012.
  8. ↑ Entry on sunflower oil. In: Römpp Online . Georg Thieme Verlag, accessed on May 16, 2012.
  9. ^ A b c Keyword "Oleic Acid" In: Hans Zoebelein (Ed.): Dictionary of Renewable Resources. 2nd edition, Wiley-VCH, Weinheim / New York 1996, ISBN 3-527-30114-3 , p. 92.
  10. ^ Keyword "Olein" In: Hans Zoebelein (Ed.): Dictionary of Renewable Resources. 2nd edition, Wiley-VCH, Weinheim / New York 1996, ISBN 3-527-30114-3 ; P. 92.
  11. ↑ B. Breuer, T. Stuhlfauth, HP Fock: Separation of Fatty Acids or Methyl Esters Including Positional and Geometric Isomers by Alumina Argentation Thin-Layer Chromatography. In: Journal of Chromatographic Science . 25, 1987, pp. 302-306, doi : 10.1093 / chromsci / 25.7.302 .
  12. ^ Brockhaus ABC chemistry. VEB FA Brockhaus Verlag, Leipzig 1965, p. 1245.

Web links

Wiktionary: Oleic acid  - explanations of meanings, origins of words, synonyms, translations