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Methylparaben (Methyl 4-hydroxybenzoate) - CAS 99-76-3

Methylparaben (Methyl 4-Hydroxybenzoate) CAS 99-76-3: Properties

1. Introduction

Methyl 4-hydroxybenzoate (commonly referred to as methylparaben) belongs to the paraben group – esters of para-hydroxybenzoic acid. This compound is registered in the international registry under CAS number 99-76-3. It is known as a safe preservative with pronounced antimicrobial activity and minimal impact on the organoleptic properties of products.

2. Chemical Structure and Physicochemical Properties

Structural formula: The molecule is the methyl ester of 4-hydroxybenzoic acid: HO–C₆H₄–COOCH₃

Key characteristics:

  • Molecular weight: ~152.15 g/mol

  • Melting point: 125–128°C

  • Solubility: Moderate in water (at elevated temperature), good in alcohols and essential oils.

Stability: Resistant to hydrolysis in many aqueous solutions under weak acidic and neutral pH conditions, but may decompose under strongly alkaline conditions. Retains activity over extended periods in products, extending their shelf life.

3. Antimicrobial Properties

Spectrum of action: Methylparaben is effective against many Gram-positive and Gram-negative bacteria, as well as various molds and yeasts.

Mechanism: By penetrating microbial membranes, it disrupts their enzyme systems, leading to inhibition of growth and reproduction.

Combination with other parabens: Often used together with propylparaben and ethylparaben to provide broad antimicrobial coverage at relatively low concentrations.

4. Applications

4.1. Pharmaceutical industry:

  • Preservation of liquid forms: Syrups, tinctures, and oral solutions often contain methylparaben to prevent bacterial and fungal growth.

  • Ointments and creams: Added to dermatological preparations to extend shelf life and maintain stability of active components.

4.2. Cosmetics and personal care products:

  • Creams and lotions: Protects emulsions from microbial spoilage and prevents changes in odor and color.

  • Shampoos and conditioners: Prevents fungal growth in water-based products, especially in humid bathroom environments.

4.3. Food industry:

  • Soft drinks: May be used (though less frequently than sodium benzoate) to prevent mold development, particularly at neutral pH.

  • Baked goods and confectionery: In some cases, added to suppress yeasts and molds, though more commonly used in cosmetics and pharmaceuticals.

5. Safety and Regulatory Aspects

Toxicological profile: Methylparaben is considered safe when used within permitted limits. However, it may occasionally provoke allergic skin reactions, particularly in sensitive individuals.

Regulation: Maximum permitted levels of parabens, including methylparaben, are established in many countries for cosmetic and food products.

Quality control: Pharmacopoeias and standards (USP, EP) regulate the purity, identification, and quantitative determination of methylparaben in pharmaceutical preparations.

6. Conclusion

Methyl 4-hydroxybenzoate (CAS 99-76-3) is an effective and widely used preservative in the pharmaceutical, cosmetic, and food industries. Its low toxicity at recommended concentrations and good antimicrobial spectrum make methylparaben one of the most popular agents for combating microbial spoilage. At the same time, individual sensitivity and compliance with regulatory standards must be taken into account.

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