Palmitic acid

Palmitic acid, or hexadecanoic acid in IUPAC nomenclature, is one of the most common saturated fatty acids found in animals and plants. Its molecular formula is CH3(CH2)14CO2H. As its name indicates, it is a major component of the oil from palm trees (palm oil, palm kernel oil, and coconut oil). Palmitate is a term for the salts and esters of palmitic acid. The palmitate anion is the observed form of palmitic acid at basic pH.

Occurrence and production
Palmitic acid mainly occurs as its ester in triglycerides (fats), especially palm oil but also tallow. The cetyl ester of palmitic acid (cetyl palmitate) occurs in spermiceti. It was discovered by Edmond Frémy in 1840, in saponified palm oil.

Palmitic acid is prepared by treating fats and oils with water at a high pressure and temperature (above 200 °C), leading to the hydrolysis of triglycerides. The resulting mixture is then distilled.

Biochemistry
Excess carbohydrates in the body are converted to palmitic acid. Palmitic acid is the first fatty acid produced during fatty acid synthesis and from which longer fatty acids can be produced. 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. 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 mainly used to produce soaps, cosmetics, and release agents. For these applications, the palmitic acid is neutralized with sodium hydroxide to give sodium palmitate. The most common route to sodium palmitate is saponification, in which palm oil, rendered from the coconut palm nut, is treated with concentrated sodium hydroxide (in the form of caustic soda or lye), which causes hydrolysis of the ester groups. This procedure splits the ester groups in the oil into glycerol and sodium palmitate.

Because it is inexpensive and benign, palmitic acid and its sodium salt find wide use including foodstuffs. Sodium palmitate is permitted as a natural additive in organic products.

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.

Napalm
Aluminum salts of palmitic acid and naphthenic acid were combined during World War II to produce napalm concentrate (aluminum naphthenate and aluminum palmitate).

Dietary effect
Retinyl palmitate is an antioxidant and 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.

According to the World Health Organization, consumption of palmitic acid may increase cholesterol levels, implying an increased risk of developing cardiovascular diseases. The report does not cite any studies that actually found a link between palmitic acid intake and patient outcomes. Another study showed that palmitic acid has no hypercholesterolaemic effect if intake of linoleic acid, an essential fatty acid, is greater than 4.5% of energy. On the other hand, it was shown that, if the diet contains trans fatty acids, the health effects are negative, causing an LDL cholesterol increase and HDL cholesterol decrease.