Zinc stearate

• BPZinc Stearate
• Ph. Eur.Zinc Stearate
• USP–NFZinc Stearate

dibasic zinc stearate; octadecanoic acid, zinc salt; zinc distearate; zinc octadecanoate; zinci stearas

Octadecanoic acid zinc salt · [557-05-1]

UNII H92E6QA4FV · PubChem CID 11178

C36H70O4Zn · 632.33

Lubricant

Typical concentrations: 0.5–1.5% · Dosage forms: Solid

Used mainly as a lubricant in tablet and capsule manufacture, at concentrations up to about 1.5% w/w. It is also used in topical dusting powders and as a thickening and opacifying agent in creams and cosmetics, where it gives slip and water repellency.

A fine, white, bulky, hydrophobic powder, free from grittiness, with a faint characteristic odour. It is greasy to the touch and adheres to the skin. The material is a mixture of zinc salts of fatty acids, mainly stearic and palmitic acids.

Melting point

about 120–130 °C

Zinc content

10.0–12.0% (Ph. Eur.)

Solubility

practically insoluble in water, ethanol and ether; soluble in hot aromatic solvents such as benzene

Stable. Store in a well-closed container in a cool, dry place.

Decomposed by dilute acids, which liberate stearic acid. Incompatible with strong oxidising agents.

Prepared by precipitation from aqueous solutions of sodium stearate and a soluble zinc salt such as zinc sulfate, or by direct reaction of zinc oxide with molten stearic acid.

Regarded as non-toxic and non-irritant after oral use at the levels used in medicines. Inhalation of the fine powder can cause pneumonitis, and fatal cases in infants who accidentally inhaled zinc stearate dusting powders led to its removal from baby powders.

Observe normal precautions for the quantity handled. Avoid inhaling the dust; eye protection, gloves and a dust respirator are recommended, with adequate ventilation.

GRAS listed. Included in the FDA Inactive Ingredient Database (oral capsules and tablets; topical preparations) and in non-parenteral medicines licensed in Europe.

Calcium stearate; magnesium stearate; stearic acid.

Like magnesium stearate, zinc stearate is hydrophobic and over-mixing can reduce tablet strength and slow dissolution, so it should be added last and blended briefly. It is less widely used than magnesium stearate in modern formulations.