Dipropylene Glycol  or DPG  is a chemical compound consisting of three isomers.

The name defines the structure of the molecule

• "Di" indicates the presence of two units of propylene glycol in the molecule.
• "Propylene" is a hydrocarbon, an isomer of propene and is used as a monomer in the production of polymers.
• "Glycol" refers to a class of organic compounds that contain two alcohol groups (-OH).

Description of raw materials used in production

• Propene - A gaseous hydrocarbon that is the starting point for the production of propylene glycol and its derivatives.
• Water - Used in the hydration process.

Step-by-step summary of industrial chemical synthesis process.

• Hydration - Propene is reacted with water to form propylene glycol (PG).
• Heating - The propylene glycol is heated in the presence of a catalyst to form a mixture of various products, including Dipropylene Glycol and higher molecular weight products.
• Distillation - The resulting mixture is distilled to separate Dipropylene Glycol from the other products.
• Purification - The Dipropylene Glycol is further purified to remove any impurities.
• Cooling - The pure Dipropylene Glycol is cooled and condensed.
• Quality Control - The final product undergoes various quality checks to ensure it meets specifications.

It appears as a colourless liquid.

What it is used for and where

Cosmetics

Fragrance. It plays a very important role in the formulation of cosmetic products as it allows perfume to be enhanced, masked or added to the final product, improving its commercial viability.  The consumer always expects to find a pleasant scent in a cosmetic product.

Perfuming. Unlike fragrance, which can also contain slightly less pleasant or characteristic odours, the term perfume indicates only very pleasant fragrances.

Solvent. It is the substance for dissolving or dispersing surfactants, oils, dyes, flavourings, bactericidal preservatives in solution.

Viscosity control agent. It controls and adapts viscosity to the required level for optimal chemical and physical stability of the product and dosage in gels, suspensions, emulsions, solutions. 

Other applications :

• Machine Tool Oils
• Hydraulic brake fluids
• Printing inks
• Insecticides
• resins, plasticisers, polyurethanes

Commercial applications

Solvent in Cosmetic and Skin Care Products. Dipropylene Glycol is used in creams, lotions, and serums to enhance the solubility of other ingredients.

Ingredient in Fragrances and Colognes. Used as a carrier and solvent for active ingredients in perfumes.

Humectant Agent. Used in skin care products to help retain moisture and improve product texture.

Solvent in Industrial Cleaning Products. Used in industrial cleaners and solvents for its ability to dissolve oils and greases.

Component in E-cigarette Liquids. Used as a base in some e-liquid formulations.

Safety

Studies on the subject are divided: some consider Dipropylene Glycol an allergen (1), others claim it is safe (2).

"Dipropylene glycol, studies"

• Molecular Formula: C₆H₁₄O₃
• Linear Formula: HOC₃H₆OC₃H₆OH
• Molecular Weight: 134.17 g/mol
• CAS: 25265-71-8
• EC Number:   246-770-3

 Synonyms:

• 3,3,5-Trimethylcyclohexyl dipropylene glycol
• Dipropylene glycol,3,5-trimethylcyclohexyl ester
• 2-Propanol,3,5-trimethylcyclohexyl)oxy]propoxy]-
• 2-Propanol, 1-(2-((3,3,5-trimethylcyclohexyl)oxy)propoxy)-
• 2-Propanol, 1-(2-((3,3,5-trimethylcyclohexyl)oxy)propoxy)-
• 1-{2-[(3,3,5-trimethylcyclohexyl)oxy]propoxy}propan-2-ol
• Dipropylene glycol, 3,3,5-trimethylcyclohexyl ester

References_____________________________________________________________________

(1) McGowan MA, Scheman A, Jacob SE. Propylene Glycol in Contact Dermatitis: A Systematic Review. Dermatitis. 2018 Jan-Feb;29(1):6-12. doi: 10.1097/DER.0000000000000307. 

Abstract. Propylene glycol (PG), an emollient and emulsifier found in cosmetics, medications, and food, has been granted the dubious honor of being named the American Contact Dermatitis Society's Allergen of the Year for 2018. Contact, systemic, and irritant cutaneous reactions have been documented for PG, which has become an increasingly common ingredient. Propylene glycol is as contentious as it is ubiquitous because it acts as both a weak sensitizer and an irritant, confounding the results of positive patch tests. This review serves to delve into what we know about PG from previous reports and studies so that providers will have a better understanding of PG contact dermatitis.

(2) Fiume MM, Bergfeld WF, Belsito DV, Hill RA, Klaassen CD, Liebler D, Marks JG Jr, Shank RC, Slaga TJ, Snyder PW, Andersen FA. Safety assessment of propylene glycol, tripropylene glycol, and PPGs as used in cosmetics. Int J Toxicol. 2012 Sep-Oct;31(5 Suppl):245S-60S. doi: 10.1177/1091581812461381. PMID: 23064775.

Abstract. Propylene glycol is an aliphatic alcohol that functions as a skin conditioning agent, viscosity decreasing agent, solvent, and fragrance ingredient in cosmetics. Tripropylene glycol functions as a humectant, antioxidant, and emulsion stabilizer. Polypropylene glycols (PPGs), including PPG-3, PPG-7, PPG-9, PPG-12, PPG-13, PPG-15, PPG-16, PPG-17, PPG-20, PPG-26, PPG-30, PPG-33, PPG-34, PPG-51, PPG-52, and PPG-69, function primarily as skin conditioning agents, with some solvent use. The majority of the safety and toxicity information presented is for propylene glycol (PG). Propylene glycol is generally nontoxic and is noncarcinogenic. Clinical studies demonstrated an absence of dermal sensitization at use concentrations, although concerns about irritation remained. The CIR Expert Panel determined that the available information support the safety of tripropylene glycol as well as all the PPGs. The Expert Panel concluded that PG, tripropylene glycol, and PPGs ≥3 are safe as used in cosmetic formulations when formulated to be nonirritating.