Palmitic acid

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]

Palmitic acid^[1]

Names
Preferred IUPAC name Hexadecanoic acid
Other names Palmitic acid C16:0 (Lipid numbers)
Identifiers
CAS Number	57-10-3 Y
3D model (JSmol)	Interactive image
ChEMBL	ChEMBL82293 N
ChemSpider	960 N
ECHA InfoCard	100.000.284
IUPHAR/BPS	1055
PubChem CID	985
UNII	2V16EO95H1 Y
CompTox Dashboard (EPA)	DTXSID2021602
InChI InChI=1S/C16H32O2/c1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16(17)18/h2-15H2,1H3,(H,17,18) N Key: IPCSVZSSVZVIGE-UHFFFAOYSA-N N InChI=1/C16H32O2/c1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16(17)18/h2-15H2,1H3,(H,17,18) Key: IPCSVZSSVZVIGE-UHFFFAOYAJ
SMILES CCCCCCCCCCCCCCCC(=O)O
Properties
Chemical formula	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)[4]
Boiling point	351–352 °C (664–666 °F; 624–625 K)[5] 271.5 °C (520.7 °F; 544.6 K), 100 mmHg[2] 215 °C (419 °F; 488 K), 15 mmHg
Solubility in water	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)[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]
Magnetic susceptibility (χ)	−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)[8]
Std molar entropy (S⦵298)	452.37 J/(mol·K)[8]
Std enthalpy of formation (ΔfH⦵298)	−892 kJ/mol[8]
Std enthalpy of combustion (ΔcH⦵298)	10030.6 kJ/mol[3]
Hazards
GHS labelling:
Pictograms	[2]
Signal word	Warning
Hazard statements	H319[2]
Precautionary statements	P305+P351+P338[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

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]

Dietary palmitic acid intake is associated with an increased cardiovascular disease risk through raising low-density lipoprotein.^[13]

Occurrence and production

Palmitic acid was discovered by saponification of palm oil, which process remains today the primary industrial route for producing the acid.^[14] Triglycerides (fats) in palm oil are hydrolysed by high-temperature water and the resulting mixture is fractionally distilled.^[15]

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).^[16] Karukas contain 44.90% palmitic acid.^[17] The cetyl ester of palmitic acid, cetyl palmitate, occurs in spermaceti.

Palmitic acid content of common foods

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:[18]

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,^[19] and it is a major, but highly variable, lipid component of human breast milk.^[20] Palmitic acid comprises nearly half of total human brain saturated fatty acids.^[21]

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.^[22] 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.^[23]

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.^[24]

Research

It is well accepted in the medical community that palmitic acid from dietary sources raises low-density lipoprotein (LDL) and total cholesterol.^{[18][25][26][27]} The World Health Organization have stated there is convincing evidence that palmitic acid increases cardiovascular disease risk.^[28] Palmitic acid intake is associated with an increased cancer risk, including prostate cancer.^[29][30]

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.^[31]

See also

• Retinyl palmitate
• Ascorbyl palmitate
• SN2 Palmitate
• Juniperic acid (16-hydroxypalmitic acid)