Propyl Gallate

Preparation

Produced commercially by the esterification of gallic acid with propyl alcohol followed by distillation to remove the excess alcohol.

Production Methods

Propyl gallate is prepared by the esterification of 3,4,5-trihydroxybenzoic acid (gallic acid) with n-propanol. Other alkyl gallates are prepared similarly using an appropriate alcohol of the desired alkyl chain length.

General Description

Fine white to creamy-white crystalline powder. Odorless or with a faint odor. Melting point 150°C. Insoluble in water. Slightly bitter taste.

Air & Water Reactions

Insoluble in water.

Reactivity Profile

Propyl gallate can react with oxidizing agents. Incompatible with strong acids, strong bases and strong reducing agents. Darkens in the presence of iron and iron salts. Contact with metals should be avoided .

Hazard

Use in foods restricted to 0.02% of fat con- tent.

Fire Hazard

Propyl gallate is combustible.

Flammability and Explosibility

Notclassified

Pharmaceutical Applications

Propyl gallate has become widely used as an antioxidant in cosmetics, perfumes, foods, and pharmaceuticals since its use in preventing autoxidation of oils was first described in 1943.It is primarily used, in concentrations up to 0.1% w/v, to prevent the rancidity of oils and fats;it may also be used at concentrations of 0.002% w/v to prevent peroxide formation in ether, and at 0.01% w/v to prevent the oxidation of paraldehyde. Synergistic effects with other antioxidants such as butylated hydroxyanisole and butylated hydroxytoluene have been reported. Propyl gallate is also said to possess some antimicrobial properties; Studies have shown that, when added to powder blends containing ketorolac, propyl gallate significantly increases the drug stability in the preparation. Other alkyl gallates are also used as antioxidants and have approximately equivalent antioxidant properties when used in equimolar concentration; however, solubilities vary; Propyl gallate has also been investigated for its therapeutic properties, mainly in animal studies.

Contact allergens

This gallate ester (E 311) is an antioxidant frequently used in the food, cosmetic, and pharmaceutical industries to prevent the oxidation of unsaturated fatty acids into rancid-smelling compounds. It causes cosmetic dermatitis mainly from lipsticks and induced contact dermatitis in a baker, and in a female confectioner, primarily sensitized by her night cream, who fried doughnuts the margarine probably containing gallates.

Biochem/physiol Actions

An antioxidant that exhibits antimicrobial activity. Propyl gallate has been reported to be an effective antioxidant-based hepatoprotector, both in vitro and in vivo. It has also been shown to prevent neuronal apoptosis and block the death of neurons exposed to FeSO4/GA as well as partially protect endothelial cells against TNF-induced apoptosis.

Toxicology

Propyl gallate (n-propyl-3,4,5-trihydroxybenzoate) is used in vegetable oils and butter. When 1.2 or 2.3% propyl gallate was added to feed for rats, loss of weight was observed. This may be due to the rats reluctance to eat food that was contaminated with the bitter taste of propyl gallate. When it was given for 10 to 16 months at the 2 to 3% level, 40% of the rats died within the first month and the remainder showed severe growth inhibition. Autopsies of rats indicated kidney damage resulting from the ingestion of propyl gallate. However, no other animal studies show serious problems and further studies indicated that propyl gallate does not cause serious chronic toxicities.

Safety Profile

Poison by ingestion and intraperitoneal routes. Experimental teratogenic and reproductive effects. Questionable carcinogen with experimental tumorigenic data. Mutation data reported. Combustible when exposed to heat or flame; can react with oxidizing materials. When heated to decomposition it emits acrid smoke and irritating fumes.

Safety

It has been reported, following animal studies, that propyl gallate has a strong contact sensitization potential.Propyl gallate has also produced cytogenic effects in CHO-K1 cells.However, despite this, there have been few reports of adverse reactions to propyl gallate.Those that have been described include contact dermatitis, allergic contact dermatitis,and methemoglobinemia in neonates. The WHO has set an estimated acceptable daily intake for propyl gallate at up to 1.4 mg/kg body-weight. (cat, oral): 0.4 g/kg (mouse, oral): 1.7 g/kg (rat, oral): 2.1 g/kg (rat, IP): 0.38 g/kg

storage

Propyl gallate is unstable at high temperatures and is rapidly destroyed in oils that are used for frying purposes. The bulk material should be stored in a well-closed, nonmetallic container, protected from light, in a cool, dry place.

Purification Methods

Crystallise the ester from aqueous EtOH or *C6H6 (m 146-146.5o). [Beilstein 10 III 2078, 10 IV 2003.]

Incompatibilities

The alkyl gallates are incompatible with metals, e.g. sodium, potassium, and iron, forming intensely colored complexes. Complex formation may be prevented, under some circumstances, by the addition of a sequestering agent, typically citric acid. Propyl gallate may also react with oxidizing materials.

Regulatory Status

GRAS listed. Accepted for use as a food additive in Europe. Included in the FDA Inactive Ingredients Database (IM injections; oral, and topical preparations). Included in nonparenteral medicines licensed in the UK. Included in the Canadian List of Acceptable Non-medicinal Ingredients.