Butylparaben (Butyl p-hydroxybenzoate) CAS 94-26-8

Butylparaben (Butyl p-hydroxybenzoate) – Broad-Spectrum Preservative for Pharmaceuticals, Cosmetics, and Food

Basic Information

• CAS Number: 94-26-8

• Molecular Formula: C₁₁H₁₄O₃

• Molecular Weight: 194.23 g/mol

• Synonyms: Butyl 4-hydroxybenzoate, Butyl parahydroxybenzoate, E209

• Appearance: White crystalline powder

• Melting Point: 68–71°C

• Solubility: Slightly soluble in water; freely soluble in ethanol, propylene glycol, and other organic solvents

• Storage: Store in a cool, dry place, protected from light and moisture

Overview
Butylparaben (butyl p‑hydroxybenzoate) is a widely used preservative belonging to the paraben family. It is the butyl ester of p‑hydroxybenzoic acid and is valued for its broad‑spectrum antimicrobial activity against bacteria, yeasts, and molds. It is commonly employed in pharmaceuticals, cosmetics, and food products to extend shelf life and prevent microbial contamination. At approved concentrations, butylparaben is considered safe and effective.

Mechanism of Action
Butylparaben inhibits microbial growth by disrupting cell membrane integrity and interfering with enzyme systems essential for microbial metabolism. Its effectiveness is enhanced at acidic to neutral pH (optimal range 4–8) and is often combined with other parabens (e.g., methylparaben, propylparaben) for synergistic protection against a wider range of microorganisms.

Applications

• Pharmaceuticals: Used as a preservative in topical creams, ointments, ophthalmic solutions, syrups, and injectable formulations.

• Cosmetics and personal care: Incorporated into lotions, creams, shampoos, makeup, sunscreens, and wet wipes to prevent microbial contamination.

• Food industry: Used as a preservative (E209) in sauces, dressings, baked goods, beverages, and other processed foods (subject to regional regulations).

• Other: Occasionally used in industrial products such as adhesives and paints.

Pharmacokinetics and Metabolism
Upon absorption, butylparaben is rapidly hydrolyzed to p‑hydroxybenzoic acid, which is conjugated (e.g., with glucuronic acid) and excreted primarily in urine. Its metabolism and elimination are well‑characterized. The half‑life is relatively short, contributing to low tissue accumulation at recommended usage levels.

Safety and Regulatory Status

• Toxicological profile: At recommended concentrations, butylparaben does not exhibit significant toxicity. Some studies have discussed potential weak estrogen‑like activity, but clinical relevance at approved levels remains debated.

• Allergic reactions: Contact dermatitis is the most commonly reported reaction, but it is rare.

• Regulatory status: Approved in many countries for use in pharmaceuticals, cosmetics, and food, with periodic review of regulations. Manufacturers are required to list parabens on product labels.

• Trends: Ongoing research focuses on alternative preservatives (e.g., sorbic acid, benzoates, organic acids) and encapsulation technologies to reduce required dosages and minimize potential side effects.

Handling and Storage

• Store in a cool, dry place, protected from light and moisture.

• Keep containers tightly sealed to prevent contamination.

• Use appropriate personal protective equipment (gloves, safety goggles, dust mask) when handling.

• Avoid inhalation of dust and contact with skin and eyes.

Quality Assurance
Each batch is tested for purity (by HPLC), melting point, heavy metals, and microbial quality to ensure compliance with pharmaceutical, cosmetic, and food-grade standards.