The molecular structure of 1,2-Propanediol contains a chiral carbon atom. It is a hygroscopic viscous liquid with a slightly spicy taste. Its specific gravity is 1.036 (25/4°C), and its freezing point is -59°C. Its boiling point is 188.2°C and 83.2°C (1,333 Pa). It is miscible with water, acetone, ethyl acetate, and chloroform and soluble in ether. It can dissolve in many essential oils but is not miscible with petroleum ether, paraffin, and grease. It is relatively stable to heat and light and more stable at low temperatures. The left-handed isomer has a boiling point of 187-189°C and an optical rotation of [α]D20-15.0°.
High temperatures can cause propylene glycol to oxidize and produce formaldehyde, lactic acid, acetone, and acetic acid. At 200°C and 1-20 MPa, 1,2-propanol can be made by hydrating epoxy propylene. The waste emission is small, the equipment corrosion is slight, the product purity is high, and the stability is vital. Still, the reaction is relatively harsh, and the equipment investment is rather significant. Ester exchange method Under normal pressure and 65°C, 1,2-propanol can be obtained by ester exchange reaction of methyl sodium as a catalyst and propylene carbonate (PC) with methanol. This method has low production cost, a complex single-product refining process, relatively poor quality, severe environmental pollution, and low yield. Currently, most domestic manufacturers use the ester exchange method to produce 1,2-propanol. Direct hydrolysis or esterification can be used to hydrolyze 1,2-dichloro propane. Hydrolysis of dichloro propane can be reached directly in a weak alkaline solution. The acid salt esterifies dichloro propane to form an ester, then hydrolyzes to produce alcohol. This method has severe environmental pollution and high cost.
Propylene glycol provides numerous benefits when used as an organic solvent. The stability of poorly soluble or water-soluble drugs can be increased using propylene glycol as a solvent, providing both rapid and sustained effects. It can soften, shape, and dissolve components of various ointments and creams. Propylene glycol can dissolve water-soluble flavors, dyes, preservatives, vitamins, resins, etc. It is an emulsifier for food and an excellent solvent for flavoring and coloring agents. Propylene glycol is a stabilizer, coagulant, antifreeze, softener, emulsifier, solvent, and carrier for edible flavors, tastes, dyes, preservatives, vanilla beans, roasted coffee beans, natural flavors, and cosmetics in cakes and daily chemicals. It includes makeup, hair care, lotions, aftershave care, deodorants, mouthwashes, and toothpaste. As a moisturizer and evener, propylene glycol is used in hair dyes. In chemistry, it serves as a wetting agent and solvent. It is a significant component of advanced antifreeze. Propylene glycol can be mixed with any proportion of water because of its low freezing point. Adding water to the coating can reduce its freezing point, enhancing its anti-freezing properties and preventing it from freezing at 0°C. Propylene glycol is easy to reach equilibrium in water-based coating systems because of its compatibility with water and high boiling point. It can also provide fluidity of the coating and slow drying.
