Propylparaben Excipient | Uses, Suppliers, and Specifications
Propylparaben is Propyl 4-hydroxybenzoate, a member of a family of alky esters of para-hydroxybenzoic acid differing by their chemical substituents on the benzene ring. It is prepared by esterifying p-hydroxybenzoic acid with n-propanol. Propylparaben occurs as a colourless powder or crystalline, odourless, and tasteless powder.
Synonyms and Trade Names: Propylparaben; Propyl Parahydroxybenzoate; Propyl Parahydroxybenzoate; Propyl p-Hydroxybenzoate; 4–Hyroxybenzoic Acid Propyl Ester; E216; Aseptoform P; CoSept P; Nipagin P; Nipasol M; Propagin; Propyl Aseptoform; Propyl Butex; Propyl Chemosept; Propyl Parasept; Solbrol P; Tegosept P; Unipthen P-23
Uses and Applications: Antimicrobial Preservative
Propylparaben (IUPAC name: 4-Hydroxybenzoic acid n-propyl ester) and also known as Propyl parahydroxybenzoate or Propyl 4-hydroxybenzoate), a member of a family of alkyl esters of para-hydroxybenzoic acid that differ at the para position of the benzene ring by various chemical substitutions. In the case of Propylparaben a propyl group is esterified with hydroxybenzoic acid giving the chemical formula C10H12O3. It is one of the commonly used parabens in pharmaceutical, cosmetic and food products.
Parabens are a family of alkylated esters of para-Hydroxybenzoic acid (PHBA), and indeed, the term ‘paraben’ is a contraction of para-Hydroxybenzoic acid, a naturally occurring substance found in several fruits and vegetables, such as berries, cucumbers and onions. Respective parabens are obtained from the formal condensation of the carboxy group of PHBA with a suitable alkanol. Parabens are possibly the most commonly used antimicrobial substances in personal care, pharmaceutical formulations and industrial products.
The antimicrobial properties of parabens and their potential as preservatives were first demonstrated in the early 1920s, and subsequently introduced into cosmetic formulations as well as pharmaceutical and food products in the 1930s. Currently, there are seven documented parabens which differ at the para position of the benzene ring by the different chemical substituents, namely:
- Isobutylparaben, and
Chemical substitutions provide each paraben with different solubility characteristics and antimicrobial activity.
In addition, 12 paraben salts are also documented and include Calcium paraben, Potassium Methylparaben, Potassium Butylparaben, Potassium Ethylparaben, Potassium Paraben, Potassium Propylparaben, Sodium Butylparaben, Sodium Ethylparaben, Sodium Isobutylparaben, Sodium Paraben, Sodium Isopropylparaben and Sodium Propylparaben.
In reality, only four parabens (and their corresponding sodium salts) are widely marketed and or approved for pharmaceutical use and include Methyl-, Ethyl-, Propyl-, and Butylparaben. Their respective structures and chemical substituents are shown below:
Parabens have come under increased scrutiny in recent years after the emergency of evidence suggesting a link between parabens and breast cancer and testosterone levels. Health authorities and the Cosmetic Ingredient Review Expert Panel have reevaluated their safety in recent years, and for now, Methyl-, Ethyl-, Propyl-, and Butylparaben are approved for use in pharmaceutical products. Methyl, Ethyl and Propylparaben are approved for cosmetics while Methylparaben can be used in certain food products.
Propylparaben occurs as colourless crystals or a white, crystalline, odourless or almost odourless, tasteless powder.
Chemical Structure & Identifiers
|Chemical Name||4-Hydroxybenzoic acid n-propyl ester|
|CAS Registry Number||[94-13-3]|
|UNII Code (FDA)||Z81X2SC10H|
Propylparaben is an approved pharmaceutical excipient and is listed in the B.P; USP-NF, Ph.Eur, J.P, I.P and ChP. It is included in the FDA Inactive Ingredients Database (covering injections, inhalation products, ophthalmic preparations, oral tablets, capsules, solutions and suspensions; otic, rectal and topical formulations). Propylparaben is also approved for use in cosmetics and other personal care and industrial products. It is affirmed GRAS (Direct Food Substances) in the USA at levels up to 0.1% and a specification for Propylparaben is in the Food Chemicals Codex FCC). In the Europe Union, Methylparaben is permitted for use in food products.
|Appearance||Colourless crystalline or a white crystalline powder|
|Bulk density||0.426 g/ml|
|Tapped density||0.706 g/ml|
|True density||1.288 g/ml|
|Boiling point||295 oC|
|Flash Point||140 oC|
|Log P (computed)||2.55|
|Dissociation constant||pKa = 8.4 (22 oC)|
|Partition coefficients||0.5 (Mineral oil: water)|
|Solubility (in 100g) 25oC
|Official name||Propylparaben||Propyl Parahydroxybenzoate||Propyl Parahydroxybenzoate|
|Melting range||96.0 – 99.0oC||96.0-99.0oC||–|
|Loss on drying||≤0.5%||–||–|
|Residue on ignition||≤0.1%||≤0.1%||–|
|Appearance of solution||+||+||+|
|Assay||98.0-102.0%||98.0 – 102.0%||98.0-102.0%|
Key: n/a Specification is not listed
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Applications in Pharmaceutical Formulations or Technology
The main use of Methylparaben in pharmaceutical products is as an antimicrobial preservative. It is also similarly used in cosmetic, food and industrial products. Parabens are generally popular because they are inexpensive, colourless, odourless, and nontoxic. They are also effective over a wide pH range and have a wide spectrum of antimicrobial activity.
While longer chained parabens possess greater antimicrobial properties, they also exhibit decreased water solubility, thus making the shorter-chained parabens, i.e Methyl and Propylparaben best suited for use in oral products. On the other hand, long-chained parabens are best suited for topical products, especially if they are rich in lipophilic content.
In general, parabens are effective against the growth of yeasts and molds at much lower concentrations compared with benzoic acid, although they are less active against bacteria, especially Gram-negative organisms. However, unlike benzoic acid, parabens retain their efficacy at pH levels of up to 8.0, making them a suitable choice for products of pH close to neutral pH.
Propylparaben is often used in combination with other parabens or antimicrobial agents due to synergistic effects that occur. Typical application levels depend greatly on the type of formulation but are usually in the 0.025 to 0.10% range (see the table below for the average usage levels across multiple product formulations):
|Dosage form||Concentration (%)|
|Oral solutions & suspensions||0.015 – 0.20|
|Topical products||0.02 – 0.3|
|Rectal products||0.10 – 0.18|
|IM, IV, SC injections||0.065 – 0.25|
|Inhalation solutions||0.025 – 0.07|
|Ophthalmic products||0.015 – 0.20|
Where solubility of a particular paraben limits usage, paraben salts (especially the sodium salt) can be used in the formulations. However, they may raise the pH of the formulation unless buffered.
Safety and Precautions
The antimicrobial properties of parabens have been known for almost a century and utilised for over nine decades. They are currently added to cosmetic, food and pharmaceutical products. The US FDA considers Methylparaben and Propylparaben to be GRAS when added to food products. Butylparaben and Ethylparaben are approved for direct addition to food. In the past parabens were used as preservatives in injections and ophthalmic preparations. They are now generally considered inappropriate for these types of dosage forms due to the irritant potential of parabens.
In spite of their effectiveness and many years of use, parabens have attracted scrutiny across the world and within the scientific community. Their potential to cause several health problems, including breast cancer, reproductive health problems and allergies has been widely discussed.
These concerns have led to a number of acute, subchronic, and chronic toxicity tests to be performed on the parabens using a wide variety of routes of administration. From these data, it has been established that parabens exhibit a very low potential of toxicity and should be considered safe in this respect for cosmetic and pharmaceutical uses in the quantities typically used as preservatives.
When tested on human skin, each of the parabens only produced evidence of irritation in concentrations that exceeded 5 to 12 per cent, which is several orders of magnitude typically used in formulations. Therefore, it has been concluded that the parabens are relatively nonirritating at the concentrations used in cosmetic products.
Parabens are considered nonteratogenic and noncarcinogenic. Sensitization is rarely observed, and they do not exhibit significant levels of photocontact sensitization or phototoxicity. However, hypersensitivity reactions, mostly of the delayed type, occurring as contact dermatitis, have been described. However, given the widespread use of parabens as preservatives, such reactions are comparatively rare. Therefore, the categorisation of parabens in certain quarters as high-rate sensitizers may be exaggerated.
Immediate hypersensitivity reactions upon injection of products formulated with parabens have also been documented. Surprisingly, products containing parabens may be used by patients who have reacted previously with contact dermatitis provided they are applied to another, unaffected, site. This phenomenon is known as the paraben paradox.
The JEFCA/WHO has set an estimated total acceptable daily intake for Methyl-, Ethyl-, and Propylparaben at up to 10mg/kg body- weight.
Toxicology: LD40 (mouse, IP): 0.96 kg
Stability and Storage Conditions
Parabens are chemically stable and effective over a wide pH range, with wide antimicrobial activity, particularly against Gram-positive bacteria and fungi (including molds). Aqueous solutions at pH 3 – 6 are stable (less than 10% decomposition) for up to about 48 months under ambient conditions. However, the same solutions maintained at ≥pH 8 undergo rapid degradation (≥10% after 2 months of storage under ambient conditions). Aqueous solutions of Methylparaben (at pH 3 – 6) can be autoclaved at 120 0C for 20 minutes, without degradation.
Propylparaben is assigned a shelf-life of 24-36 months. The bulk material should be stored in a well-dosed container in a cool, dry place. When processing the bulk material, observe applicable SHEQ protocols appropriate to the circumstances and quantity of material being handled. As Propylparaben may be an irritant to the skin, eyes, and mucous membranes, it should be handled in a well-ventilated environment. Suitable PPE (eye protection, gloves, and a dust mask or respirator) is recommended.
Sustainability and Environmental Impact
The long-term impact of parabens on human and animal health, and on ecosystems is currently a matter of great debate. There is evidence that they may be endocrine disruptors, this effect being pertinent to wastewater discharges.
Manufacturers & Suppliers
Additional Resources (Downloads)
References and Literature Used
 T.R. Aalto, M.C. Firman, N.E. Rigler, p‐Hydroxybenzoic acid esters as preservatives. I. Uses, antibacterial and antifungal studies, properties and determination, Journal of the American Pharmaceutical Association, 42 (1953) 449-457.
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