Propyl gallate, or propyl 3,4,5-trihydroxybenzoate, is an
ester
In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...
formed by the
condensation
Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapor ...
of
gallic acid
Gallic acid (also known as 3,4,5-trihydroxybenzoic acid) is a trihydroxybenzoic acid with the formula C6 H2( OH)3CO2H. It is classified as a phenolic acid. It is found in gallnuts, sumac, witch hazel, tea leaves, oak bark, and other plant ...
and
propanol
There are two isomers of propanol.
* 1-Propanol, ''n''-propanol, or propan-1-ol: CH3CH2CH2OH, the most common meaning
*2-Propanol, isopropyl alcohol, isopropanol, or propan-2-ol: (CH3)2CHOH
See also
* Propanal (propionaldehyde) differs in spel ...
. Since 1948, this
antioxidant
Antioxidants are Chemical compound, compounds that inhibit Redox, oxidation, a chemical reaction that can produce Radical (chemistry), free radicals. Autoxidation leads to degradation of organic compounds, including living matter. Antioxidants ...
has been added to foods containing oils and fats to prevent
oxidation
Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...
. As a food additive, it is used under the
E number
E numbers, short for Europe numbers, are codes for substances used as food additives, including those found naturally in many foods, such as vitamin C, for use within the European Union (EU) and European Free Trade Association (EFTA). Commonly ...
E310.
Description
Propyl gallate is an antioxidant. It protects against oxidation by
hydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...
and oxygen free radicals. It appears as a white to creamy-white crystalline odorless solid.
Propyl gallate (PG) is a white to nearly white odorless crystalline powder that has slightly bitter taste and darkens in the presence of iron salts. It is an irritant that can cause skin dryness, dermatitis, and sensitization. Inhalation may cause chemical pneumonia
Production
Propyl gallate does not occur naturally, and is prepared either from reactions with
gallic acid
Gallic acid (also known as 3,4,5-trihydroxybenzoic acid) is a trihydroxybenzoic acid with the formula C6 H2( OH)3CO2H. It is classified as a phenolic acid. It is found in gallnuts, sumac, witch hazel, tea leaves, oak bark, and other plant ...
enzyme catalysis
Enzyme catalysis is the increase in the rate of a process by an "enzyme", a biological molecule. Most enzymes are proteins, and most such processes are chemical reactions. Within the enzyme, generally catalysis occurs at a localized site, calle ...
of
tannic acid
Tannic acid is a specific form of tannin, a type of polyphenol. Its weak acidity (Acid dissociation constant, pKa around 6) is due to the numerous phenol groups in the structure. The chemical formula for commercial tannic acid is often given as ...
. Syntheses with gallic acid have been the most prominent methods of production, and include
Steglich esterification
The Steglich esterification is a variation of an esterification with dicyclohexylcarbodiimide as a coupling reagent and 4-dimethylaminopyridine as a catalyst. The reaction was first described by Wolfgang Steglich in 1978. It is an adaptation o ...
thionyl chloride
Thionyl chloride is an inorganic compound with the chemical formula . It is a moderately Volatility (chemistry), volatile, colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a Halogenation, chlorinating reagen ...
, and
Fischer esterification
Fischer is a German occupational surname, meaning fisherman. The name Fischer is the fourth most common German surname. The English version is Fisher.
People with the surname A
* Abraham Fischer (1850–1913) South African public official
* ...
with various catalysts.
Uses
Propyl gallate is used to protect oils and fats in products from oxidation; it is used in foods, cosmetics, hair products, adhesives, biodiesel, and lubricants. It is often used interchangeably with
octyl gallate
Octyl gallate is the ester of 1-octanol and gallic acid. As a food additive, it is used under the E number E311 as an antioxidant and preservative.
Properties
Octyl gallate is a white powder with a characteristic odor. It is very slightly solub ...
and
dodecyl gallate
Dodecyl gallate, or lauryl gallate, is the ester of dodecanol and gallic acid. As a food additive it is used under the E number E312 as an antioxidant and preservative
A preservative is a substance or a chemical that is added to products such ...
in these applications.
Propyl gallate is an antioxidant that neutralizes free radicals, which are unstable molecules that can damage cells, proteins, and DNA. It is used as a
triplet state
In quantum mechanics, a triplet state, or spin triplet, is the quantum state of an object such as an electron, atom, or molecule, having a quantum spin ''S'' = 1. It has three allowed values of the spin's projection along a given axis ''m''S = � ...
fluorescence microscopy
A fluorescence microscope is an optical microscope that uses fluorescence instead of, or in addition to, scattering, reflection, and attenuation or absorption, to study the properties of organic or inorganic substances. A fluorescence micro ...
.
Biological effects
A 1993 study in fat rodents found little or no effect on carcinogenesis by propyl gallate.
A 2009 study found that propyl gallate acts as an
estrogen
Estrogen (also spelled oestrogen in British English; see spelling differences) is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three ...