Sorbitan isostearate is a non-ionic surfactant and emulsifier derived from the esterification of sorbitol, a sugar alcohol, with isostearic acid, a branched fatty acid. This compound is used primarily in cosmetic and personal care products for its ability to stabilize emulsions, allowing oil and water-based components to mix smoothly. It is considered a mild and skin-friendly ingredient, making it suitable for various formulations, including lotions, creams, and makeup. Sorbitan isostearate is biodegradable and is often used in products that aim to be more eco-friendly.

Chemical Composition and Structure
Sorbitan isostearate is a complex ester of sorbitol and isostearic acid. The sorbitol backbone, a polyol (sugar alcohol), is esterified with isostearic acid, a C18 branched-chain fatty acid, giving the compound its amphiphilic properties. The hydrophilic portion (sorbitol) allows for water affinity, while the hydrophobic portion (isostearic acid) interacts with oils and fats, making it a versatile emulsifying agent.

Physical Properties
Sorbitan isostearate typically appears as a pale yellow or amber waxy solid or semi-solid at room temperature. It has a mild odor and is soluble in oils and organic solvents but is dispersible in water when used in combination with other emulsifiers. It has a melting point range of about 45-55°C. Due to its hydrophobic and hydrophilic properties, it functions effectively as a stabilizer in oil-in-water and water-in-oil emulsions.

Production Process
The production of sorbitan isostearate involves the following key steps:

1. Esterification: Sorbitol, a sugar alcohol derived from glucose, is reacted with isostearic acid in a controlled environment to form the ester compound.

2. Refining: The resulting product undergoes refining and purification to ensure the removal of any residual reactants or byproducts.

3. Formulation and Packaging: Once purified, sorbitan isostearate is prepared for incorporation into various cosmetic and personal care formulations, ensuring stability and efficacy.

Applications

• Cosmetics: Sorbitan isostearate is widely used in skin care and hair care formulations, including creams, lotions, sunscreens, and conditioners. Its primary function is to act as an emulsifier, ensuring that the oil and water components in a formulation remain mixed and stable. This helps create smooth, homogeneous products that maintain their consistency over time. It also contributes to the moisturizing properties of emulsions by allowing for even distribution of oils on the skin.

Cosmetic - INCI Functios:

Surfactant - Emulsifying agent. Emulsions are thermodynamically unstable and are used to soothe or soften the skin and emulsify, so they need a specific, stabilising ingredient. This ingredient forms a film, lowers the surface tension and makes two immiscible liquids miscible. A very important factor affecting the stability of the emulsion is the amount of the emulsifying agent. Emulsifiers have the property of reducing the oil/water or water/oil interfacial tension, improving the stability of the emulsion and also directly influencing the stability, sensory properties and surface tension of sunscreens by modulating the filmometric performance.

• Makeup: In makeup formulations, sorbitan isostearate helps stabilize liquid foundations, lipsticks, and blushes, preventing separation and ensuring smooth application. It contributes to the texture and spreadability of these products.

• Pharmaceuticals: Sorbitan isostearate is also used as an emulsifying agent in pharmaceutical creams and ointments, enhancing the stability and absorption of active ingredients.

• Eco-friendly Products: Due to its biodegradability, sorbitan isostearate is commonly found in formulations designed to be environmentally friendly, particularly in natural and organic cosmetic lines.

Environmental and Safety Considerations
Sorbitan isostearate is generally regarded as safe for use in cosmetics and personal care products. It is considered mild and non-irritating to the skin, making it suitable for sensitive skin formulations. The ingredient is also biodegradable, reducing its environmental impact when used in personal care products that wash off into water systems. Despite its safety, as with any ingredient, it should be used in accordance with regulatory guidelines to prevent potential irritation in individuals with particularly sensitive skin.

From an environmental perspective, sorbitan isostearate is favored for its sustainability profile, as it is derived from natural sources (sorbitol from plant-based glucose and isostearic acid from fatty acids). Its biodegradability ensures minimal long-term impact on ecosystems, making it a responsible choice for eco-conscious formulations.

Molecular Formula  C₂₄H₄₆O₆

Molecular Weight  430.626 g/mol

CAS  54392-26-6

Synonyms :

• [(1R)-1-[(2S,3R,4S)-3,4-dihydroxyoxolan-2-yl]-2-hydroxyethyl] 16-methylheptadecanoate
• Sorbitan,isooctadecanoate
• SCHEMBL15578308

References______________________________________________________________________

Lanigan RS, Yamarik TA Final report on the safety assessment of sorbitan caprylate, sorbitan cocoate, sorbitan diisostearate, sorbitan dioleate, sorbitan distearate, sorbitan isostearate, sorbitan olivate, sorbitan sesquiisostearate, sorbitan sesquistearate, and sorbitan triisostearate. Cosmetic Ingredient Review Expert panel.  Int J Toxicol. 2002;21 Suppl 1:93-112. Review.