CID 985

C₁₆H₃₂O₂

Palmitic acid

C 16
H 32
O 2

Ball-and-stick Stick Space-filling

Drag to rotate; pinch or Ctrl + scroll to zoom. Arrow keys rotate, + − zoom, R resets.

50 atoms, 49 bonds.

IUPAC name: hexadecanoic acid
Molar mass: 256.430(40) g/mol
Atoms: 50
SMILES: CCCCCCCCCCCCCCCC(=O)O
InChIKey: IPCSVZSSVZVIGE-UHFFFAOYSA-N
PubChem CID: 985

Made of

C H O

Structural formula of palmitic acid. Each unlabelled corner is a carbon atom, and the 28 hydrogens on carbon are not drawn. It shows which atoms are joined to which, not the shape. The model above shows the shape.

In palmitic acid, hexadecanoic acid by its IUPAC name, a long, unbranched chain of carbon atoms ends in a carboxyl group, –COOH. ChEBI, a reference database of biological molecules, classes the compound as a saturated long-chain fatty acid with sixteen carbons in a straight row. Saturated means that no carbon is double-bonded to another, and the model draws all fifteen carbon-to-carbon links as single bonds. Thirty-two hydrogen atoms and two of oxygen complete the formula, C₁₆H₃₂O₂, with a molar mass of 256.43 g/mol.

ChEBI also records it as a metabolite, a product of living chemistry, in plants, algae and Daphnia magna. The pure acid forms colourless or white crystals, as the International Chemical Safety Card (ICSC) describes it. Water leaves those crystals undissolved, according to the Hazardous Substances Data Bank (HSDB). Ethanol, acetone and benzene dissolve them, and chloroform takes them up readily.

Structure and bonding

In palmitic acid, 50 atoms make one long chain, which the model stretches into a flat zig-zag. PubChem’s computed structure holds the chain fully extended. Along every run of four carbons, the twist about the middle bond stays within 4° of 180°, keeping the backbone in one plane. The methyl carbon at the tail sits 19.2 Å from the carboxyl carbon at the head. Each C–C–C angle measures 111 to 116° in the model.

With Labels on, two H symbols sit on each chain carbon and three on the methyl carbon. The head carbon holds one oxygen by a double bond and another by a single bond, the second carrying the last hydrogen. The Stick view keeps every bond, C–H included, as a thin rod, with no atom balls. Space-filling turns it into a long rod sheathed in hydrogen, the two oxygens a knob at its head.

The model shows one free, neutral molecule. In oils and fats, HSDB notes, palmitic acid is present as the glyceryl ester, joined to glycerol. ChEBI calls it the conjugate acid of hexadecanoate, the palmitate ion left once the O–H hydrogen goes. The stretched chain, too, is one computed arrangement.

Where it turns up

Palm oil and palm kernel oil contain palmitic acid, according to the NCI Thesaurus of the US National Cancer Institute. So do butter, cheese, milk and meat. MeSH, the medical subject index of the US National Library of Medicine, also places it in olive oil and body lipids. Irradiating fatty food forms 2-dodecylcyclobutanone (2-DCB) from its palmitic acid, HSDB reports.

Japan wax is mostly palmitic acid, present as glyceryl palmitate alongside stearic, oleic and japonic acids, according to HSDB. Bayberry wax, also called myrtle wax, is about 36 per cent palmitic acid and 58 per cent myristic acid. Manufacturers draw the acid from Japan wax, Chinese vegetable tallow or palm oil. From palm acid it is separated by selective crystallisation, with oleic acid coming off the same process.

Why it matters

Palmitic acid comes from the diet and from the body itself, HSDB notes. Fatty-acid synthesis starts from acetyl-CoA, an acetate group attached to coenzyme A, and runs mainly in the liver, fat tissue and mammary glands. Successive reduction and dehydration steps yield saturated chains of up to sixteen carbons, palmitic acid’s own length. A full-term newborn is 13 to 15 per cent fat. Palmitic acid makes up 45 to 50 per cent of that fat, much of it made by the foetus.

It forms part of membrane, secretory and transport lipids and of signalling molecules, and is attached to proteins in palmitoylation. Making lung lecithin, which HSDB links to foetal maturation, requires it. The body breaks palmitic acid down quickly, mostly by beta-oxidation, which cuts the chain into acetate units released as acetyl-CoA.

Dietary fat as a whole supplies energy, helps the body absorb vitamins and has a large effect on cholesterol levels, MedlinePlus says.

Properties

Properties of palmitic acid Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 985.
Property	Value	Unit	Source
Molecular formula (Hill order)	C₁₆H₃₂O₂
Molar mass	256.430(40) g/mol	g/mol	IUPAC/CIAAW 2024
Carbon atoms	16
Hydrogen atoms	32
Oxygen atoms	2
Bonds	49
Single bonds	48
Double bonds	1
PubChem molecular weight	256.42 g/mol	g/mol	PubChem

Safety

In food, cosmetics and soap, palmitic acid is essentially harmless; the US Environmental Protection Agency’s Safer Choice programme has verified it as a chemical of low concern. The pure powder is combustible, though, and its dust can explode when mixed with air, in the ICSC’s wording. Under a third of company reports to the European Chemicals Agency class it as irritating to skin, eyes or airways under the Globally Harmonized System (GHS). The PubChem Laboratory Chemical Safety Summary for palmitic acid gathers these classifications.

Questions

What does the structure of palmitic acid look like?

In PubChem's 3D model it is a straight, fully stretched zig-zag of sixteen carbon atoms ending in a carboxyl group, –COOH. Every bond between two carbons is single, which is what makes it a saturated fatty acid. At the head, the model's C=O double bond measures 1.225 Å and its C–O single bond 1.356 Å, with an angle of 123° between them.

Why is palmitic acid a solid at room temperature?

It does not melt until 62.49 °C on the Hazardous Substances Data Bank's measurement, or 63 °C on the International Chemical Safety Card. The reason, in Chem1's account, is shape. A straight saturated chain lets neighbouring molecules line up side by side and pack efficiently, which makes the longer saturated fatty acids waxy solids.

What is palmitic acid used for?

The Hazardous Substances Data Bank lists the manufacture of soaps, lubricating oils, waterproofing and metallic palmitates such as aluminium palmitate. It is also a starting material for esters, isopropyl palmitate among them, and an ingredient of cosmetics such as cleansing cream. Haz-Map lists surface coatings, where it acts as a non-drying oil, and the NORMAN network classes it as a mould-release agent for plastics.

Is palmitic acid safe as a food additive?

The US Food and Drug Administration permits it for direct addition to food, according to the Hazardous Substances Data Bank, with flavouring, lubricant or release agent and surface-active agent among its roles. JECFA, the food-additive expert committee of the Food and Agriculture Organization and the World Health Organization, evaluated it as a flavouring in 1997 and found no safety concern. The Cosmetic Ingredient Review panel judges it safe in cosmetics formulated not to irritate or sensitise.

Made of the same elements

C₁₈H₃₄O₂ Oleic acid 54 atoms, 53 bonds.
C₂₁H₃₀O₂ Progesterone 53 atoms, 56 bonds.
C₁₉H₂₈O₂ Testosterone 49 atoms, 52 bonds.
C₂₁H₃₀O₅ Cortisol 56 atoms, 59 bonds.
C₁₈H₂₄O₂ Estradiol 44 atoms, 47 bonds.
C₁₅H₁₆O₂ Bisphenol A 33 atoms, 34 bonds.
C₁₃H₁₈O₂ Ibuprofen 33 atoms, 33 bonds.
C₁₀H₂₀O Menthol 31 atoms, 31 single bonds.

All 51 compounds made of carbon, hydrogen and oxygen

C₁₄H₁₄O₃ Naproxen 31 atoms, 32 bonds.
C₁₂H₂₂O₁₁ Lactose 45 atoms, 46 single bonds.
C₁₂H₂₂O₁₁ Sucrose 45 atoms, 46 single bonds.
C₂₇H₄₄O Cholecalciferol 72 atoms, 74 bonds.
C₂₀H₁₄O₄ Phenolphthalein 38 atoms, 41 bonds.
C₂₇H₄₆O Cholesterol 74 atoms, 77 bonds.
C₉H₈O₄ Aspirin 21 atoms, 21 bonds.
C₈H₈O₃ Methyl salicylate 19 atoms, 19 bonds.
C₈H₈O₃ Vanillin 19 atoms, 19 bonds.
C₆H₁₂O₆ Fructose 24 atoms, 24 single bonds.
C₆H₁₂O₆ Glucose 24 atoms, 24 single bonds.
C₄H₉OH 1-Butanol 15 atoms, 14 single bonds.
C₆H₅COOH Benzoic acid 15 atoms, 15 bonds.
C₂H₅OC₂H₅ Diethyl ether 15 atoms, 14 single bonds.
C₆H₅CHO Benzaldehyde 14 atoms, 14 bonds.
C₃H₇COOH Butyric acid 14 atoms, 13 bonds.
CH₃COOC₂H₅ Ethyl acetate 14 atoms, 13 bonds.
C₇H₆O₃ Salicylic acid 16 atoms, 16 bonds.
C₄H₈O Butanone 13 atoms, 12 bonds.
C₆H₅OH Phenol 13 atoms, 13 bonds.
C₃H₈O₂ Propylene glycol 13 atoms, 12 single bonds.
C₃H₇OH 1-Propanol 12 atoms, 11 single bonds.
C₆H₈O₆ Ascorbic acid 20 atoms, 20 bonds.
C₃H₈O₃ Glycerol 14 atoms, 13 single bonds.
C₃H₈O Isopropyl alcohol 12 atoms, 11 single bonds.
C₆H₈O₇ Citric acid 21 atoms, 20 bonds.
C₂H₅COOH Propionic acid 11 atoms, 10 bonds.
C₃H₆O Acetone 10 atoms, 9 bonds.
C₂H₆O₂ Ethylene glycol 10 atoms, 9 single bonds.
C₃H₆O₃ Lactic acid 12 atoms, 11 bonds.
CH₃OCH₃ Dimethyl ether 9 atoms, 8 single bonds.
C₂H₅OH Ethanol 9 atoms, 8 single bonds.
C₄H₆O₅ Malic acid 15 atoms, 14 bonds.
CH₃COOH Acetic acid 8 atoms, 7 bonds.
C₄H₆O₆ Tartaric acid 16 atoms, 15 bonds.
CH₃CHO Acetaldehyde 7 atoms, 6 bonds.
C₂H₄O Ethylene oxide 7 atoms, 7 single bonds.
C₂H₄O₃ Glycolic acid 9 atoms, 8 bonds.
CH₃OH Methanol 6 atoms, 5 single bonds.
HCOOH Formic acid 5 atoms, 4 bonds.
H₂CO₃ Carbonic acid 6 atoms, 5 bonds.
CH₂O Formaldehyde 4 atoms, 3 bonds.
H₂C₂O₄ Oxalic acid 8 atoms, 7 bonds.