Sodium methyl p-hydroxybenzoate , best known as Sodium Methylparaben is a widely used preservative in the food, cosmetic, and pharmaceutical industries. It belongs to the paraben family and is used to prevent the growth of bacteria, mold, and fungi, thereby extending the shelf life of products. E219 is commonly found in water-based products such as beverages, cosmetics, medicines, and packaged foods.

Chemical Composition and Structure

Sodium Methylparaben is the sodium salt of methyl p-hydroxybenzoate. Its chemical structure includes a benzene ring, a hydroxyl group, and an ester group. The sodium form increases its water solubility, making it ideal for use in liquid products or aqueous formulations. E219 works by inhibiting microbial growth through the destabilization of microbial cell membranes.

Physical Properties

Sodium Methylparaben is a white, odorless crystalline powder that is highly soluble in water. Due to its high solubility, it is easily incorporated into various formulations, especially in water-containing products such as beverages, creams, lotions, and syrups.

Production Process
Sodium Methylparaben is produced through the esterification of p-hydroxybenzoic acid with methanol, followed by neutralization with sodium hydroxide to form the sodium salt. This process enhances the solubility of the compound, facilitating its inclusion in aqueous formulations.

The name defines the structure of the molecule:

• Sodium (Na). Sodium is an alkaline metal, a group of highly reactive elements found in group 1 of the periodic table. Sodium is soft and silvery-white in color. It is highly reactive, especially with water, and is commonly found in salts and minerals.
• Methylparaben refers to the methyl ester of p-hydroxybenzoic acid. Parabens are a type of preservative used in a variety of cosmetic and pharmaceutical products.

Description of the raw materials used in its production.

• Methylparaben acid - This is the primary active ingredient that, once neutralized, becomes the preservative known as Sodium Methylparaben. It has antimicrobial and fungicidal properties.
• Sodium hydroxide (or lye) - Used as a neutralizing agent. When added to methylparaben acid, it neutralizes it to form the salt, Sodium Methylparaben.
• Water - Serves as a solvent and reaction medium. It facilitates the mixing and reaction between the methylparaben acid and sodium hydroxide.

The synthesis process takes place in several stages:

• Preparation. Methylparaben is synthesized by esterification of p-hydroxybenzoic acid with methanol. This reaction is usually catalyzed by an acid and involves heating the reagents to promote the reaction.
• Neutralization. Methylparaben is neutralized with sodium hydroxide (NaOH) to produce sodium methylparaben with salt formation from the acid (Methylparaben ) and base (NaOH). The reaction is carried out in an aqueous solution.
• Crystallization. Sodium Methylparaben is isolated from the reaction mixture by crystallization. This involves cooling the reaction mixture to induce the formation of Sodium Methylparaben crystals.
• Filtration and drying. Sodium Methylparaben crystals are separated from the reaction mixture by filtration and dried to remove all remaining water.
• Quality control test. The final product is tested to ensure it meets the required specifications with tests for purity, moisture content and other physical and chemical properties.

It occurs in the form of a fine white powder.

Applications

• Food Industry: Sodium Methylparaben is used as a preservative in various packaged foods and beverages such as juices, jams, sauces, and confectioneries to extend their shelf life by preventing microbial growth.

• Cosmetics: In cosmetic products like creams, lotions, shampoos, and makeup, E219 is used to prevent bacterial and fungal contamination, ensuring product safety and efficacy.

• Pharmaceuticals: It is used as a preservative in syrups, mouthwashes, and liquid medicines to ensure that they remain free from contamination throughout their shelf life.

It is a preservative used in food, pharmaceuticals, cosmetics and more.

Cosmetics

It is a restricted ingredient as V/12 a Relevant Item in the Annexes of the European Cosmetics Regulation 1223/2009. Substance or ingredient reported:  4-Hydroxybenzoic acid and its Methyl- and Ethyl-esters, and their salts

• Preservative. Any product containing organic, inorganic compounds, water, needs to be preserved from microbial contamination. Preservatives act against the development of harmful microorganisms and against oxidation of the product.

Pharmaceuticals 

• Sodium Methylparaben is used as a preservative in oral solutions, such as those containing sodium valproate. An HPLC method was developed for the simultaneous determination of sodium valproate, methylparaben, and propylparaben in oral solutions

Safety in Use
Sodium Methylparaben is considered safe for use in food and cosmetic products at approved concentrations. However, like other parabens, its use has been the subject of debate due to potential links to skin sensitization or endocrine disruption. Most regulatory authorities, including the European Food Safety Authority (EFSA) and the Food and Drug Administration (FDA), consider Sodium Methyl p-Hydroxybenzoate safe when used within established limits.

Allergic Reactions
Some individuals may be sensitive to parabens, including Sodium Methylparaben. Allergic reactions, though rare, can include contact dermatitis, particularly in people with sensitive skin or a predisposition to allergies. It is recommended to test new products containing parabens on a small area of skin before widespread use.

Toxicity and Carcinogenicity
There is no conclusive evidence that Sodium Methylparaben is carcinogenic at approved concentrations for use in food and cosmetics. However, parabens have been the focus of scientific scrutiny for their potential effects on the endocrine system, as they can weakly mimic estrogen. Regulatory authorities closely monitor the use of parabens like E219, limiting their concentration in products to ensure consumer safety.

Environmental and Safety Considerations
Sodium Methylparaben is biodegradable and does not pose significant environmental risks when used in regulated amounts. However, the use of parabens is under increasing environmental scrutiny due to their potential accumulation in aquatic systems, which is why responsible use is advised.

Regulatory Status
Sodium Methylparaben is regulated and approved for use in the European Union and United States as a food and cosmetic preservative. Maximum allowable concentrations are set by food and cosmetic safety regulations to prevent adverse effects on human health.

Sodium Methylparaben as a preservative is widely used in our life, but health problems could arise if the human body absorbs it in quantity. So there are strict rules about the dosage of Sodium Methylparaben in each country (1).

Parabens

Parabens are chemical preservative compounds that have been the subject of attention in the scientific literature as possible endocrine disruptors (particularly propylparaben and butylparaben), i.e. with the possibility of damaging the hormone-producing glands in our bodies, particularly in the breasts. The 2004 study by Darbre et al. showed that parabens remain in our bodies as intact esters (2). Following this study, some of the scientific literature in 2005 and 2006 cast doubt on Darbre's conclusions and claimed they were limited. However, both the US FDA and the European SCCP authorised in 2006 the use of a single paraben in cosmetic products at a concentration of 0.4% and the use of total parabens at a concentration of 0.8% (3). However, there is no shortage of studies that consider the restrictions unnecessary: M. G. Kirchhof et al. in 2013 found that parabens are among the safest and most well-tolerated preservatives and that current data do not support drastic regulations or personal exposure restrictions (4). Darbre in 2014 published a further study in which he showed how parabens can cause DNA damage (5).

Sodium Methylparaben studies

Typical optimal commercial product characteristics Sodium methylparaben

Appearance	White fine powder
Boiling Point	265.5ºC at 760 mmHg
Melting Point	>125°C
Flash Point	116.4ºC
pH	9.5-10.5 (1g/l, H2O)
Sulphate	≤0.12%
Chloride	≤350ppm
PSA	49.36000
LogP	1.61700
Water%	5.0 Max.
Heavy metal (Pb, ppm)	10 Max.
Safety

• Molecular Formula   C₈H₇O₃Na   C₈H₇NaO₃
• Molecular Weight   174.131 g/mol
• Exact Mass   174.029282
• UNII    CR6K9C2NHK
• CAS    5026-62-0
• EC Number: 225-714-1
• DSSTox Substance ID  DTXSID1042156
• IUPAC  sodium;4-methoxycarbonylphenolate
• InChI=1S/C8H8O3.Na/c1-11-8(10)6-2-4-7(9)5-3-6;/h2-5,9H,1H3;/q;+1/p-1  
• InChl Key      PESXGULMKCKJCC-UHFFFAOYSA-M
• SMILES   COC(=O)C1=CC=C(C=C1)[O-].[Na+]
• PubChem Substance ID 329769369
• MDL number MFCD00016470
• Beilstein Registry Number 4165000

Synonyms:

• Methyl 4-hydroxybenzoate sodium salt
• Sodium 4-(methoxycarbonyl)phenolate
• Sodium methylparaben
• Methylparaben sodium
• Methylparaben, sodium salt
• sodium;4-methoxycarbonylphenolate
• Sodium Methyl Parahydroxybenzoate
• sodium 4carbomethoxyphenolate
• Methyl p-hydroxybenzoate, sodium salt
• Sodium p-methoxycarbonylphenoxide
• Sodium methyl p-hydroxybenzoate
• Benzoic acid, 4-hydroxy-, methyl ester, sodium salt
• Sodium methyl 4-hydroxybenzoate
• sodium 4-methoxycarbonylphenolate
• Methyl p-hydroxybenzoate sodium
• Preserval MS
• Solparol
• Bonomold OMNa
• Methyl 4-hydroxybenzoate sodium salt
• Sodium 4-carbomethoxyphenolate

Bibliografia_______________________________________________

(1) Wang ST, Chen DY, Hou PG, Wang XL, Wang ZF, Wei M. Determination of the Sodium Methylparaben Content Based on Spectrum Fluorescence Spectral Technology and GA-BP Neural Network. Guang Pu Xue Yu Guang Pu Fen Xi. 2015 Jun;35(6):1606-10. 

(2) Darbre PD, Aljarrah A, Miller WR, Coldham NG, Sauer MJ, Pope GS. Concentrations of parabens in human breast tumours. J Appl Toxicol. 2004 Jan-Feb;24(1):5-13. doi: 10.1002/jat.958.

(3) https://www.fda.gov/cosmetics/cosmetic-ingredients/parabens-cosmetics

Cosmetic Ingredient Review Expert Panel. Final amended report on the safety assessment of Methylparaben, Ethylparaben, Propylparaben, Isopropylparaben, Butylparaben, Isobutylparaben, and Benzylparaben as used in cosmetic products. Int J Toxicol. 2008;27(Suppl 4):1-82.

(4) Kirchhof MG, de Gannes GC. The health controversies of parabens. Skin Therapy Lett. 2013 Feb;18(2):5-7.

(5) Darbre PD, Harvey PW. Parabens can enable hallmarks and characteristics of cancer in human breast epithelial cells: a review of the literature with reference to new exposure data and regulatory status. J Appl Toxicol. 2014 Sep;34(9):925-38. doi: 10.1002/jat.3027.

Harvey PW. Parabens, oestrogenicity, underarm cosmetics and breast cancer: a perspective on a hypothesis. J Appl Toxicol. 2003 Sep-Oct;23(5):285-8. doi: 10.1002/jat.946. PMID: 12975767.

Harvey PW, Everett DJ. Significance of the detection of esters of p-hydroxybenzoic acid (parabens) in human breast tumours. J Appl Toxicol. 2004 Jan-Feb;24(1):1-4. doi: 10.1002/jat.957. PMID: 14745840.