Glycerol (Glycerin)

Glycerin is primarily derived as a by-product of the soap industry; specifically, it is obtained by removing fatty acids from the filtrate resulting from the saponification of fats and oils. The pH of this solution is then adjusted to 8–9 using sodium hydroxide to precipitate iron ions, followed by concentration to yield crude glycerin, which is subsequently decolorized and distilled to produce pure glycerin. Additionally, glycerin can be prepared from natural sources—for instance, through the fermentation of sugar beet molasses in the presence of a large excess of sodium sulfite. In terms of chemical synthesis, glycerin can also be produced via the chlorination and subsequent saponification of propylene.
Glycerin is widely utilized in oral, otic, ophthalmic, topical, and parenteral pharmaceutical formulations. It serves primarily as an antimicrobial preservative, emollient, humectant, component in ophthalmic preparations, plasticizer for tablet film coatings, solvent for injectable medications, and sweetener in various formulations. In topical pharmaceutical preparations and cosmetics, glycerin functions primarily as a humectant and emollient. In injectable formulations, it serves predominantly as a solvent. In oral liquid preparations, glycerin acts as a solvent, sweetener, antimicrobial preservative, and thickening agent; it is also employed as a plasticizer in film coatings. Furthermore, glycerin is used as a plasticizer in soft gelatin capsules and suppositories. Glycerin is extensively incorporated into clinical therapeutic formulations and is also utilized as a food additive.