Palmitic acid

Palmitic acid, or hexadecanoic acid in IUPAC nomenclature, 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 is 16:0. As its name indicates, it is a major component of the oil from the fruit of oil palms (palm oil). Palmitic acid can also be found in meats, cheeses, butter, and other dairy products. Palmitates are the salts and esters of palmitic acid. The palmitate anion is the observed form of palmitic acid at physiologic pH (7.4).

Palmitic acid[1]
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
IUPHAR/BPS
CompTox Dashboard (EPA)
Properties
C16H32O2
Molar mass 256.430 g·mol−1
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) [4]
Boiling point 351–352 °C (664–666 °F; 624–625 K) [5]
271.5 °C (520.7 °F; 544.6 K)
at 100 mmHg[2]
215 °C (419 °F; 488 K)
at 15 mmHg
0.46 mg/L (0 °C)
0.719 mg/L (20 °C)
0.826 mg/L (30 °C)
0.99 mg/L (45 °C)
1.18 mg/L (60 °C)[6]
Solubility soluble in amyl acetate, alcohol, CCl4,[6] 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)[7]
Solubility in methyl acetate 7.81 g/100 g[6]
Solubility in ethyl acetate 10.7 g/100 g[6]
Vapor pressure 0.051 mPa (25 °C)[3]
1.08 kPa (200 °C)
28.06 kPa (300 °C)[8]
Acidity (pKa) 4.75 [3]
-198.6·10−6 cm3/mol
1.43 (70 °C)[3]
Viscosity 7.8 cP (70 °C)[3]
Thermochemistry
463.36 J/mol·K[8]
Std molar
entropy (So298)
 452.37 J/mol·K[8]
-892 kJ/mol[8]
Std enthalpy of
combustion (ΔcH⦵298)
 10030.6 kJ/mol[3]
Hazards
GHS pictograms [2]
GHS Signal word Warning
GHS hazard statements
 H319[2]
GHS precautionary statements
 P305+351+338[2]
NFPA 704 (fire diamond)
1
1
0
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).
N verify (what is YN ?)
Infobox references

Aluminium salts of palmitic acid and naphthenic acid were combined during World War II to produce napalm. The word "napalm" is derived from the words naphthenic acid and palmitic acid.

Occurrence and production

Palmitic acid was discovered by Edmond Frémy in 1840, in saponified palm oil.[11] This remains the primary industrial route for its production, with the triglycerides (fats) in palm oil being hydrolysed by high temperature water (above 200 °C or 390 °F), and the resulting mixture fractionally distilled to give the pure product.[12]

Palmitic acid is naturally produced by a wide range of other plants and organisms, typically at low levels. It is naturally present in butter, cheese, milk, and meat, as well as cocoa butter, soybean oil, and sunflower oil. Karukas contain 44.90% palmitic acid.[13] The cetyl ester of palmitic acid (cetyl palmitate) occurs in spermaceti.

Biochemistry

Excess carbohydrates in the body are converted to palmitic acid. 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,[14] and it is a major, but highly variable, lipid component of human breast milk.[15] 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.[16] In biology, some proteins are modified by the addition of a palmitoyl group in a process known as palmitoylation. Palmitoylation is important for membrane localisation of many proteins.

Applications

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 tree (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.

Because it is inexpensive and adds texture and "mouth feel" 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.[17] The aluminium salt is used as a thickening agent of napalm used in military actions.

Hydrogenation of palmitic acid yields cetyl alcohol, which is used to produce detergents and cosmetics.

Recently, a long-acting antipsychotic medication, paliperidone palmitate (marketed as INVEGA Sustenna), used in the treatment of schizophrenia, has been synthesized using the oily palmitate ester as a long-acting release carrier medium when injected intramuscularly. The underlying method of drug delivery is similar to that used with decanoic acid to deliver long-acting depot medication, in particular, neuroleptics such as haloperidol decanoate.

Health effects

According to the World Health Organization, evidence is "convincing" that consumption of palmitic acid increases the risk of developing cardiovascular disease,[18] based on studies indicating that it may increase LDL levels in the blood. Retinyl palmitate is a source of vitamin A added to low-fat milk to replace the vitamin content lost through the removal of milk fat. Palmitate is attached to the alcohol form of vitamin A, retinol, to make vitamin A stable in milk.

See also
  • Retinyl palmitate
  • Ascorbyl palmitate

References
  1. Merck Index, 12th Edition, 7128.
  2. Sigma-Aldrich Co., Palmitic acid. Retrieved on 2014-06-02.
  3. CID 985 from PubChem
  4. Beare-Rogers, J.; Dieffenbacher, A.; Holm, J.V. (2001). "Lexicon of lipid nutrition (IUPAC Technical Report)". Pure and Applied Chemistry. 73 (4): 685–744. doi:10.1351/pac200173040685.
  5. Palmitic acid at Inchem.org
  6. "Palmitic acid".
  7. Seidell, Atherton; Linke, William F. (1952). Solubilities of Inorganic and Organic Compounds. Van Nostrand. Retrieved 2014-06-02.
  8. n-Hexadecanoic acid in Linstrom, Peter J.; Mallard, William G. (eds.); NIST Chemistry WebBook, NIST Standard Reference Database Number 69, National Institute of Standards and Technology, Gaithersburg (MD), http://webbook.nist.gov (retrieved 2014-05-11)
  9. Gunstone, F. D., John L. Harwood, and Albert J. Dijkstra. The Lipid Handbook, 3rd ed. Boca Raton: CRC Press, 2007. ISBN 0849396883 | ISBN 978-0849396885
  10. The most common fatty acid is the monounsaturated oleic acid. See: https://pubchem.ncbi.nlm.nih.gov/compound/965#section=Top
  11. Frémy, E. (1842). "Memoire sur les produits de la saponification de l'huile de palme". Journal de Pharmacie et de Chimie. XII: 757.
  12. Anneken, David J.; Both, Sabine; Christoph, Ralf; Fieg, Georg; Steinberner, Udo; Westfechtel, Alfred (2006). "Fatty Acids". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a10_245.pub2. ISBN 978-3527306732.
  13. Purwanto, Y.; Munawaroh, Esti (2010). "Etnobotani Jenis-Jenis Pandanaceae Sebagai Bahan Pangan di Indonesia" [Ethnobotany Types of Pandanaceae as Foodstuffs in Indonesia] (PDF). Berkala Penelitian Hayati (in Indonesian). 5A: 97–108. doi:10.5072/FK2/Z6P0OQ. ISSN 2337-389X. OCLC 981032990. Retrieved 25 October 2018.
  14. Kingsbury, K. J.; Paul, S.; Crossley, A.; Morgan, D. M. (1961). "The fatty acid composition of human depot fat". Biochemical Journal. 78 (3): 541–550. doi:10.1042/bj0780541. PMC 1205373. PMID 13756126.
  15. Jensen, RG; Hagerty, MM; McMahon, KE (June 1978). "Lipids of human milk and infant formulas: a review". Am. J. Clin. Nutr. 31 (6): 990–1016. doi:10.1093/ajcn/31.6.990. PMID 352132.
  16. Fatty acid biosynthesis - Reference pathway
  17. US Soil Association standard 50.5.3
  18. Diet, Nutrition and the Prevention of Chronic Diseases, WHO Technical Report Series 916, Report of a Joint WHO/FAO Expert Consultation, World Health Organization, Geneva, 2003, p. 88 (Table 10)

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