Glycerin

• BPGlycerol
• JPGlycerin
• Ph. Eur.Glycerol
• USP–NFGlycerin

Croderol; glycerine; glycerol; glycerolum; 1,2,3-propanetriol; trihydroxypropane glycerol; E422

Propane-1,2,3-triol · [56-81-5]

UNII PDC6A3C0OX · PubChem CID 753

C3H8O3 · 92.09

Solvent, humectant

Typical concentrations: up to 30% as humectant · Dosage forms: Liquid, Semi-solid

Used in a wide range of oral, ophthalmic, otic, topical and parenteral products as a solvent, co-solvent, humectant, plasticiser, sweetener and tonicity agent. Typical concentrations: antimicrobial preservative < 20%; emollient and humectant ≤ 30%; aqueous gel vehicle 5–15%; non-aqueous gel vehicle 50–80%; ophthalmic preparations 0.5–3%; solvent in parenteral products ≤ 50%; sweetener in alcoholic elixirs ≤ 20%. It is also used as a plasticiser in film coatings and soft gelatin capsule shells.

A clear, colourless, odourless, viscous and hygroscopic liquid with a sweet taste, roughly 0.6 times as sweet as sucrose.

Boiling point

about 290 °C, with decomposition

Melting point

about 18 °C; may crystallise on prolonged cooling

Density

≈ 1.26 g/cm³ at 20 °C

Viscosity

≈ 1.4 Pa·s at 20 °C; falls sharply with added water

Refractive index

≈ 1.474 at 20 °C

Solubility

miscible with water and ethanol; practically insoluble in fixed oils, chloroform and benzene

Hygroscopic. Pure glycerin is not readily oxidised under ordinary storage, but it decomposes on heating with formation of toxic acrolein. Mixtures with water, ethanol and propylene glycol are chemically stable. Glycerin that has crystallised on cold storage should be warmed to about 20 °C to melt it before use. Store in an airtight container in a cool, dry place.

May react explosively with strong oxidising agents such as chromium trioxide, potassium chlorate and potassium permanganate. Traces of iron cause darkening of mixtures containing phenols, salicylates or tannin. With boric acid it forms a complex (glyceroboric acid) that is a stronger acid than boric acid itself. Light-induced black discoloration occurs with bismuth subnitrate or zinc oxide.

Obtained mainly as a by-product of the hydrolysis, saponification or transesterification of vegetable and animal fats and oils (soap, fatty acid and biodiesel production), then purified by distillation. It can also be synthesised from propene.

Generally regarded as non-toxic and non-irritant at the levels used as an excipient. Large oral doses may cause headache, thirst, nausea and hyperglycaemia, and it has a laxative effect when given rectally. Parenteral administration of concentrated solutions can cause haemolysis, haemoglobinuria and renal damage. Undiluted glycerin is mildly irritant to skin and mucosa because it draws water from tissues.

Observe normal precautions for the quantity handled; eye protection and gloves are recommended. Glycerin is combustible and should be kept away from strong oxidising agents.

GRAS listed. Accepted as a food additive in Europe (E422). Included in the FDA Inactive Ingredient Database (dental, inhalation, injectable, nasal, ophthalmic, oral, otic, rectal, topical, transdermal and vaginal products) and in parenteral and non-parenteral medicines licensed in Europe.

Propylene glycol; polyethylene glycol; sorbitol; glyceryl monostearate.

Glycerin contaminated with diethylene glycol (DEG) or ethylene glycol has caused fatal mass poisonings, mostly in children taking oral syrups. Current USP–NF and Ph. Eur. monographs include tests that limit these impurities, and every incoming lot should be tested accordingly. Pharmacopoeial grades of different strength exist (for example glycerol 85% in Ph. Eur.).