Butylparaben Excipient | Uses, Suppliers, and Specifications
Butylparaben is Butyl 4-hydroxybenzoate, a member of a family of alky esters of para-hydroxybenzoic acid differing by their chemical substituents on the benzene ring. Butylparaben occurs as a colourless powder or crystalline, odourless, and tasteless powder.
Synonyms and Trade Names: Butylparaben, Butyl p-hydroxybenzoate; 4-Hydroxybenzoic Acid Butyl Ester; Nipabutyl; Tegosept B; Unisept B; CoSept® B
Pharmacopoeial Compliance: USP-NF; Ph. Eur; JP; IP
Uses and Applications: Antimicrobial Preservatives in Pharmaceutical and Cosmetic Products
Butylparaben (IUPAC name: Butyl 4-hydroxybenzoate, and also known as Butyl 4-hydroxybenzoate, Butyl p-hydroxybenzoate or 4-hydroxybenzoic acid butyl ester) is a member of a family of alkyl esters of para-hydroxybenzoic acid commonly known commonly as parabens. Butylparaben is known to occur naturally albeit to a limited extent in shrubs native in South East Asia (e.g Strychnos cathayensis Merr.). The commercial grade is, however, obtained synthetically from the formal condensation of the carboxy group of 4-hydroxybenzoic acid with ethanol. It is one of the parabens approved for use as an antimicrobial preservative in pharmaceutical 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 their use 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 still approved for use in pharmaceutical products. Methyl, Ethyl and Propylparaben are approved for cosmetic and food use.
Butylparaben is supplied as an odourless, colourless crystalline or a white crystalline powder.
Chemical Structure & Identifiers
|CAS Registry Number||[94-26-8]|
|Regulatory Status||PhEur; USP-NF; JPE|
|UNII Code (FDA)||3QPI1U3FVB|
Butylparaben is an approved pharmaceutical excipient and is currently 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, oral tablets, capsules, solutions and suspensions; and topical formulations). Butylparaben is also approved for use in cosmetics and other personal care and industrial products.
|Physical form||Solid, powder|
|Appearance||Colourless crystals or a white, crystalline powder|
|Bulk density||0.731 g/ml|
|Tapped density||0.819 g/ml|
|Melting point||68-71 oC|
|Flash Point||68-71 oC|
|Log P (octanol/water)||3.57|
|Partition coefficients||Values depending on type of oil|
|Solubility (in 100g)
|Official name||Butylparaben||Butyl Hydroxybenzoate||Butyl Parahydroxybenzoate||Butyl Parahydroxybenzoate|
|Appearance of solution||specified||specified||specified||specified|
|Residue on ignition||≤0.1%||n/a||n/a||≤0.1%|
|Assay (dried basis)||98.0 – 102.0%||98.0 – 102.0%||98.0 – 102.0%||98.0 – 102.0%|
Key: n/a Specification is not listed
*All claims with respect to conformity are subject to our Terms and Conditions. No express or implied warranty is made for specific properties or fitness for any particular application or purpose.
Applications in Pharmaceutical Formulations or Technology
The main use of Butylparaben in pharmaceutical products is as an antimicrobial preservative. It is also similarly used in cosmetic and industrial products. Like other parabens, Butylparaben is popular because its inexpensive, colourless, odourless, and nontoxic. It is also effective over a wide pH range and has a wide spectrum of antimicrobial activity.
As a long-chained paraben, it possesses greater antimicrobial properties but has decreased water solubility, thus it is ideally suited for topical products while shorter-chained parabens, i.e Methyl and Propylparaben are best suited for use in oral products.
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.
Butylparaben can be used alone or 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 0.005 to 0.40% range (for example, in topical products, Butylparaben has been used at a concentration of 0.02-0.4%, while in oral suspensions, the concentrations were 0.006-0.05%).
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 dosage forms due to their irritant potential.
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.
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).
Butylparaben 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. To prevent irritation to the skin, eyes, and mucous membranes, the material 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
A sustainability assessment for Butylparaben is yet to be undertaken. However, 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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