Hexylene glycol is a glycol chemical compound in which the two hydroxy groups are in the 2 and 4 positions of 2-methylpentane (isopentane).

Hexylene Glycol is a synthetic glycol used primarily as a solvent, surfactant emulsifying, and viscosity agent in cosmetic formulations. It is valued for its ability to enhance product texture and moisture retention while improving the stability of formulations.

Chemical Composition and Structure

The chemical composition of Hexylene Glycol includes:

• Hexylene Glycol: A diol with a six-carbon chain, known for its solvent properties and ability to dissolve other ingredients.

Structurally, Hexylene Glycol features two hydroxyl (–OH) groups attached to a hexane backbone, contributing to its effectiveness as a humectant and solvent.

Physical Properties

• Appearance: Typically a clear, colorless liquid.
• Solubility: Soluble in water and organic solvents, making it versatile for various formulations.
• pH: Generally neutral, around 6-7.
• Odor: Mild, characteristic of glycols.
• Stability: Stable under normal storage conditions; should be protected from extreme temperatures.

Production Process

• Synthesis: Hexylene Glycol is produced through the reaction of acetylene and formaldehyde or by the hydrogenation of 1,2-hexanediol.
• Purification: The resulting product is purified to remove any unreacted materials and impurities.
• Formulation: The purified Hexylene Glycol is incorporated into cosmetic products, often combined with other ingredients to enhance performance.

It occurs as a colourless liquid, with a typical ammonia odour, soluble in water, ethanol and most organic solvents. 

What it is used for and where it is used

Cosmetics

The main applications of Hexylene glycol (Hexylene Glycol/2-methylpentane-2,4-diol) are mainly in cosmetics as a surfactant and low molecular weight emulsifier and to add fragrance to products.

INCI Functions:

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.

Skin conditioning agent. It is the mainstay of topical skin treatment as it has the function of restoring, increasing or improving skin tolerance to external factors, including melanocyte tolerance. The most important function of the conditioning agent is to prevent skin dehydration, but the subject is rather complex and involves emollients and humectants that can be added in the formulation.

Solvent. It is the substance for dissolving or dispersing surfactants, oils, dyes, flavourings, bactericidal preservatives in solution.In fact, it dissolves other components present in a cosmetic formulation. Solvents are generally liquid (aqueous and non-aqueous).

Surfactant - Cleansing agent. Cosmetic products used to cleanse the skin utilise the surface-active action that produces a lowering of the surface tension of the stratum corneum, facilitating the removal of dirt and impurities. 

Perfuming. Unlike fragrance, which can also contain slightly less pleasant or characteristic odours, the term perfume indicates only very pleasant fragrances. Used for perfumes and aromatic raw materials.

Medicine

In pharmaceutical products it is a so-called 'intermediate product' and is included in formulas as an excipient, solvent, fragrance. It has shown better antibacterial and antifungal efficacy than propylene glycol and 1,3-butylene glycol (1).

Industrial Applications

It is a very common product and is variously employed and used as a solvent, reinforcing and bonding agent in the following products:

• lubricants and greases
• diesel and petrol antifreeze products
• adhesives and sealants
• polishes and waxes
• air care products
• washing and cleaning products
• coating products
• fillers
• fillers
• plasters
• modelling clay
• finger paints
• cosmetics and personal care products
• pH adjusters
• water treatment products
• workshop
• construction work 
• health services, scientific research and development
• textiles
• hides or fur
• chemicals

Safety

As with most chemical compounds, Hexylene glycol is no exception, albeit to a lesser extent, in cases of allergies (2).

Hexylene glycol studies

Typical optimal commercial product characteristics Hexylene glycol/2-Methyl-2,4-pentanediol

Appearance	Colorless liquid
Density	1.0±0.1 g/cm3          0.925 g/mL at 25 °C (lit.)
Boiling Point	197.5±0.0 °C at 760 mmHg
Melting Point	−40°
Flash Point	93.9±0.0°C     201 °F
Purity	≥99%
Water	≤0.5%
Acidity(mgKOH/g)	≤0.2
Vapour Pressure	0.1±0.8 mmHg at 25°C      kPa  0.006 (20°C)
Refractive Rate	n20/D1.427(lit.)
PSA	40.46000
Safety

• Molecular Formula C₆H₁₄O₂
• Linear Formula CH₃CH(OH)CH₂C(CH₃)₂OH
• Molecular Weight: 118.176 g/mol
• Exact Mass   118.099380
• UNII: KEH0A3F75J
• CAS: 107-41-5  99113-75-4
• EC Number: 203-489-0
• DSSTox Substance ID DTXSID5021885
• IUPAC  2-methylpentane-2,4-diol
• InChI=1S/C6H14O2/c1-5(7)4-6(2,3)8/h5,7-8H,4H2,1-3H3  
• InChl Key      SVTBMSDMJJWYQN-UHFFFAOYSA-N
• SMILES   CC(CC(C)(C)O)O
• PubChem Substance ID 329749326
• MDL number MFCD00004547
• Beilstein Registry Number 1098298
• ChEBI  62995
• ICSC    0660
• NSC   8098
• RTECS   SA0810000
• UN   1993
• NCI  

Synonyms: 

• 2-Methylpentane-2,4-diol
• 2-METHYL-2,4-PENTANEDIOL
• 1,1,3-trimethyl-1,3-propanediol
• (+/-)-2-Methyl-2,4-pentanediol
• 2-Methylpentan-2,4-diol
• alpha,alpha,alpha'-Trimethyltrimethylene glycol
• 1,3-dimethyl-3-hydroxybutanol
• (+-)-2-Methyl-2,4-pentanediol
• 1,3,3-trimethyl-1,3-propanediol
• 2methyl-2,4-pentanediol
• 2-methyl-2-4-pentanediol
• SCHEMBL19379
• 2,4-Pentanediol,2-methyl-
• 2-Methyl-pentane-2,4-diol
• 1,3-Trimethyltrimethylenediol
• Diolane
• Pinakon
• 2,4-Dihydroxy-2-methylpentane
• 2,4-Pentanediol, 2-methyl-
• Isol
• 4-Methyl-2,4-pentanediol
• 1,1,3-Trimethyltrimethylenediol
• 2-Methyl pentane-2,4-diol
• 2-Methyl-2,4-pentandiol

References_____________________________________________________________________

(1) Kinnunen T, Koskela M. Antibacterial and antifungal properties of propylene glycol, hexylene glycol, and 1,3-butylene glycol in vitro. Acta Derm Venereol. 1991;71(2):148-50.

Abstract. The antimicrobial properties of three glycols, - propylene glycol, hexylene glycol, and 1,3-butylene glycol - against Candida albicans, Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pyogenes A, Streptococcus mitis, and E. coli were studied in vitro. Within 20 h, 10% and 30% hexylene glycol in fresh tryptic soy broth were able to kill all the micro-organisms listed above. Five percent hexylene glycol showed some antimicrobial properties but the 1% agent had no effect. Thirty percent 1,3-butylene glycol and 30% propylene glycol were approximately as effective as 10% HG. The results speak in favour of using hexylene glycol in cosmetic and dermatological vehicles instead of propylene glycol and 1,3-butylene glycol.

(2) Spoerl D, Scherer K, Bircher AJ. Contact urticaria with systemic symptoms due to hexylene glycol in a topical corticosteroid: case report and review of hypersensitivity to glycols. Dermatology. 2010;220(3):238-42. doi: 10.1159/000275703.