Definition
ChEBI: The benzoate ester that is the propyl ester of 4-hydroxybenzoic acid. Preservative typically found in many water-based cosmetics, such as creams, lotions, shampoos and bath products. Also used as a food additive.
General Description
Colorless crystals or white powder or chunky white solid. Melting point 95-98°C. Odorless or faint aromatic odor. Low toxicity, Tasteless (numbs the tongue). pH: 6.5-7.0 (slightly acidic) in solution.
Reactivity Profile
Maximum stability of PROPYL-4-HYDROXYBENZOATE(94-13-3) occurs at a pH of 4 to 5. Incompatible with alkalis and iron salts. Also incompatible with strong oxidizing agents and strong acids .
Air & Water Reactions
Water soluble [Hawley].
Fire Hazard
Flash point data for this chemical are not available; however, PROPYL-4-HYDROXYBENZOATE is probably combustible.
Preparation
Produced by esterfying p-hydroxybenzoic acid with n-propanol, using an acid catalyst such as sulfuric acid and an excess
of propanol. The materials are heated in a glass-lined reactor under reflux. The acid is then neutralized with caustic soda and the
product is crystallized by cooling. The crystallized product is centrifuged, washed, dried under vacuum, milled and blended, all in
corrosion-resistant equipment to avoid metallic contamination.
Aroma threshold values
Detection: 20 ppb
Flammability and Explosibility
Nonflammable
Pharmaceutical Applications
Propylparaben is widely used as an antimicrobial preservative in
cosmetics, food products, and pharmaceutical formulations.
It may be used alone, in combination with other paraben esters,
or with other antimicrobial agents. It is one of the most frequently
used preservatives in cosmetics.
The parabens are effective over a wide pH range and have a
broad spectrum of antimicrobial activity, although they are most
effective against yeasts and molds.
Owing to the poor solubility of the parabens, the paraben salts,
particularly the sodium salt, are frequently used in formulations.
This may cause the pH of poorly buffered formulations to become
more alkaline.
Propylparaben (0.02% w/v) together with methylparaben
(0.18% w/v) has been used for the preservation of various
parenteral pharmaceutical formulations.
Safety
Propylparaben and other parabens are widely used as antimicrobial
preservatives in cosmetics, food products, and oral and topical
pharmaceutical formulations.
Propylparaben and methylparaben have been used as preservatives
in injections and ophthalmic preparations; however, they are
now generally regarded as being unsuitable for these types of
formulations owing to the irritant potential of the parabens.
Systemically, no adverse reactions to parabens have been
reported, although they have been associated with hypersensitivity
reactions. The WHO has set an estimated acceptable total daily
intake for methyl, ethyl, and propyl parabens at up to 10 mg/kg
body-weight.
LD50 (mouse, IP): 0.2 g/kg
LD50 (mouse, oral): 6.33 g/kg
LD50 (mouse, SC): 1.65 g/kg
storage
Aqueous propylparaben solutions at pH 3–6 can be sterilized by
autoclaving, without decomposition.At pH 3–6, aqueous
solutions are stable (less than 10% decomposition) for up to about
4 years at room temperature, while solutions at pH 8 or above are
subject to rapid hydrolysis (10% or more after about 60 days at
room temperature).
Incompatibilities
The antimicrobial activity of propylparaben is reduced considerably
in the presence of nonionic surfactants as a result of micellization.
Absorption of propylparaben by plastics has been reported, with
the amount absorbed dependent upon the type of plastic and the
vehicle. Magnesium aluminum silicate, magnesium trisilicate,
yellow iron oxide, and ultramarine blue have also been reported to
absorb propylparaben, thereby reducing preservative efficacy.
Propylparaben is discolored in the presence of iron and is subject
to hydrolysis by weak alkalis and strong acids.
Regulatory Status
Propylparaben and methylparaben are affirmed GRAS direct food
substances in the USA at levels up to 0.1%. All esters except the
benzyl ester are allowed for injection in Japan.
In cosmetics, the EU and Brazil allow use of each paraben at
0.4%, but the total of all parabens may not exceed 0.8%. The upper
limit in Japan is 1.0%.
Accepted as a food additive in Europe. Included in the FDA
Inactive Ingredients Database (IM, IV, and SC injections; inhalations;
ophthalmic preparations; oral capsules, solutions, suspensions,
and tablets; otic, rectal, topical, and vaginal preparations).
Included in parenteral and nonparenteral medicines licensed in the
UK. Included in the Canadian List of Acceptable Non-medicinal
Ingredients.
References
[1] Patent: CN106365990, 2017, A. Location in patent: Paragraph 0015; 0016; 0017; 0018; 0019; 0020; 0021-0026
[2] Journal of Pharmacy and Pharmacology, 2003, vol. 55, # 1, p. 85 - 93
[3] Synthetic Communications, 2001, vol. 31, # 16, p. 2435 - 2439
[4] Archiv der Pharmazie (Weinheim, Germany), 1938, vol. 276, p. 154,162
[5] Journal of the Society of Chemical Industry, London, 1947, vol. 66, p. 175
