Palmitic acid (hexadecanoic acid in IUPAC nomenclature) is a fatty acid with a 16-carbon chain. It is the most common saturated fatty acid found in animals, plants and microorganisms.[9][10] Its chemical formula is CH3(CH2)14COOH, and its C:D ratio (the total number of carbon atoms to the number of carbon-carbon double bonds) is 16:0. It is a major component of palm oil from the fruit of Elaeis guineensis (oil palms), making up to 44% of total fats. Meats, cheeses, butter, and other dairy products also contain palmitic acid, amounting to 50–60% of total fats.[11]
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| Names | |
|---|---|
| Preferred IUPAC name Hexadecanoic acid | |
| Other names Palmitic acid C16:0 (Lipid numbers) | |
| Identifiers | |
3D model (JSmol) | |
| ChEMBL | |
| ChemSpider | |
| ECHA InfoCard | 100.000.284 |
PubChem CID | |
| UNII | |
CompTox Dashboard (EPA) | |
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| Properties | |
| C16H32O2 | |
| Molar mass | 256.430 g/mol |
| Appearance | White crystals |
| Density | 0.852 g/cm3 (25 °C)[2] 0.8527 g/cm3 (62 °C)[3] |
| Melting point | 62.9 °C (145.2 °F; 336.0 K)[7] |
| Boiling point | 351–352 °C (664–666 °F; 624–625 K)[8] 271.5 °C (520.7 °F; 544.6 K), 100 mmHg[2] 215 °C (419 °F; 488 K), 15 mmHg |
| 4.6 mg/L (0 °C) 7.2 mg/L (20 °C) 8.3 mg/L (30 °C) 10 mg/L (45 °C) 12 mg/L (60 °C)[4] | |
| Solubility | Soluble in amyl acetate, alcohol, CCl4,[4] C6H6 Very soluble in CHCl3[3] |
| Solubility in ethanol | 2 g/100 mL (0 °C) 2.8 g/100 mL (10 °C) 9.2 g/100 mL (20 °C) 31.9 g/100 mL (40 °C)[5] |
| Solubility in methyl acetate | 7.81 g/100 g[4] |
| Solubility in ethyl acetate | 10.7 g/100 g[4] |
| Vapor pressure | 0.051 mPa (25 °C)[3] 1.08 kPa (200 °C) 28.06 kPa (300 °C)[6] |
| Acidity (pKa) | 4.75 [3] |
| −198.6·10−6 cm3/mol | |
Refractive index (nD) | 1.43 (70 °C)[3] |
| Viscosity | 7.8 cP (70 °C)[3] |
| Thermochemistry | |
Heat capacity (C) | 463.36 J/(mol·K)[6] |
Std molar entropy (S⦵298) | 452.37 J/(mol·K)[6] |
Std enthalpy of formation (ΔfH⦵298) | −892 kJ/mol[6] |
Std enthalpy of combustion (ΔcH⦵298) | 10030.6 kJ/mol[3] |
| Hazards | |
| GHS labelling: | |
 [2] | |
| Warning | |
| H319[2] | |
| P305+P351+P338[2] | |
| NFPA 704 (fire diamond) | |
| Flash point | 206 °C (403 °F; 479 K)[2] |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
Palmitates are the salts and esters of palmitic acid. The palmitate anion is the observed form of palmitic acid at physiologic pH (7.4). Major sources of C16:0 are palm oil, palm kernel oil, coconut oil, and milk fat.[12]
Occurrence and production
Palmitic acid was discovered by Edmond Frémy (in 1840) in the saponification of palm oil, which process remains today the primary industrial route for producing the acid.[13] Triglycerides (fats) in palm oil are hydrolysed by high-temperature water and the resulting mixture is fractionally distilled.[14]
Dietary sources
Palmitic acid is produced by a wide range of plants and organisms, typically at low levels. Among common foods it is present in milk, butter, cheese, and some meats, as well as cocoa butter, olive oil, soybean oil, and sunflower oil, (see table).[15] Karukas contain 44.90% palmitic acid.[16] The cetyl ester of palmitic acid, cetyl palmitate, occurs in spermaceti.
| Food | % of total calories |
|---|---|
| Palm oil | 45.1% |
| Beef tallow | 26.5% |
| Butter fat | 26.2% |
| Cocoa butter | 25.8% |
| Lard | 24.8% |
| Cottonseed oil | 24.7% |
| Chicken | 23.2% |
| Corn oil | 12.2% |
| Peanut oil | 11.6% |
| Soybean oil | 11% |
| Coconut oil | 8.4% |
| Palm kernel oil | 8% |
| Rapeseed oil | 3.6% |
| Source:[17] | |
Biochemistry
Palmitic acid is the first fatty acid produced during fatty acid synthesis and is the precursor to longer fatty acids. As a consequence, palmitic acid is a major body component of animals. In humans, one analysis found it to make up 21–30% (molar) of human depot fat,[18] and it is a major, but highly variable, lipid component of human breast milk.[19] Palmitate negatively feeds back on acetyl-CoA carboxylase (ACC), which is responsible for converting acetyl-CoA to malonyl-CoA, which in turn is used to add to the growing acyl chain, thus preventing further palmitate generation.[20]
Some proteins are modified by the addition of a palmitoyl group in a process known as palmitoylation. Palmitoylation is important for localisation of many membrane proteins.
Applications
Surfactant
Palmitic acid is used to produce soaps, cosmetics, and industrial mold release agents. These applications use sodium palmitate, which is commonly obtained by saponification of palm oil. To this end, palm oil, rendered from palm trees (species Elaeis guineensis), is treated with sodium hydroxide (in the form of caustic soda or lye), which causes hydrolysis of the ester groups, yielding glycerol and sodium palmitate.
Foods
Because it is inexpensive and adds texture and "mouthfeel" to processed foods (convenience food), palmitic acid and its sodium salt find wide use in foodstuffs. Sodium palmitate is permitted as a natural additive in organic products.[21]
Military
Aluminium salts of palmitic acid and naphthenic acid were the gelling agents used with volatile petrochemicals during World War II to produce napalm. The word "napalm" is derived from the words naphthenic acid and palmitic acid.[22]
Research
It is well accepted in the medical community that palmitic acid from dietary sources raises low-density lipoprotein (LDL) and total cholesterol.[17][23][24][25] The World Health Organization have stated there is convincing evidence that palmitic acid increases cardiovascular disease risk.[26]
A 2021 review indicated that replacing dietary palmitic acid and other saturated fatty acids with unsaturated fatty acids, such as oleic acid, could reduce several biomarkers of cardiovascular and metabolic diseases.[27]
See also
- Retinyl palmitate
- Ascorbyl palmitate
- SN2 Palmitate
- Juniperic acid (16-hydroxypalmitic acid)
References
External links
Media related to Palmitic acid at Wikimedia Commons- . Encyclopædia Britannica (11th ed.). 1911.
