Nonproprietary Names

JP: Aluminum Monostearate USP-NF: Aluminum Monostearate

Synonyms

Aluminum stearate; aluminum, dihydroxy (octadecanoate-O-); dihydroxyaluminum monostearate; HyQual; octadecanoic acid aluminum salt; stearic acid aluminum salt; stearic acid aluminum dihydroxide salt; Synpro.

Chemical Name and CAS Registry Number

Aluminum monostearate [7047-84-9]

Empirical Formula and Molecular Weight

C18H37AlO4 344.50

Structural Formula

[CH3(CH2)16COO]Al(OH)2

Functional Category

Emollient; emulsion stabilizer; gelling agent; opacifier; stabilizing agent.

Applications in Pharmaceutical Formulation or Technology

Technology Aluminum monostearate is mainly used in microencapsulation(1-3) and in the manufacture of ointments. Aluminum monostearate is used as a viscosity-increasing agent in nonaqueous cosmetic and pharmaceutical formulations. In addition, aluminum monostearate can be used as an emulsion stabilizer in cosmetic emulsions and is used in cosmetics such as mascara, moisturizers, and sunscreens.

Description

Aluminum monostearate is an aluminum compound of stearic acid and palmitic acid. The USP32–NF27 states that aluminum monostearate contains the equivalent of not less than 14.5% and not more than 16.5% of Al2O3, calculated on the dried basis. The JP XV states that it contains not less than 7.2% and not more than 8.9% of aluminium. Aluminum Monostearate Aluminum monostearate occurs as a white, fine, bulky powder with a slight odor of fatty acid. It is a solid material.

Pharmacopeial Specifications

See Table I. See also Section 18. Table I: Pharmacopeial specifications for aluminum monostearate. Test JP XV USP32–NF27 Identification Description þ43.0% þ42.0% Loss on drying Arsenic þ42 ppm — 44 ppm Heavy metals 450 ppm 450 ppm Acid value for fatty acid Free fatty acid Water-soluble salts þ þ410 mg — — — Assay of Al (dried basis) 7.2–8.9% 14.5–16.5%

Typical Properties

See Table II. Melting point 220–2258C Solubility Practically insoluble i and benzene. Specific gravity 1.14 n water. Soluble in ethanol (95%) Table II: Typical physical properties of slected commercially available aluminum monostearates. Grade Assay (as Al2O3) (%) Loss on drying (%) Median particle size (mm) Synpro Aluminum Monostearate NF 15.5 0.8 7.0 Synpro Aluminum Monostearate NF Gellant 15.3 1.6 — HyQual Aluminum Monostearate NF Powder 14.5–16.5 42.0 — HyQual Aluminum 14.5–16.5 Monostearate NF Fine Powder 42.0 —

Stability and Storage Conditions

Aluminum monostearate should be stored in a well-closed container in a cool, dry, place. It is stable under ordinary conditions of use and storage.

Incompatibilities

—

Method of Manufacture

Aluminum monostearate is prepared by reacting aluminum with stearic acid.

Safety

Aluminum monostearate is generally regarded as relatively nontoxic and nonirritant when used as an excipient.

Handling Precautions

Observe normal precautions appropriate to the circumstances and quantity of the material handled. When heated to decomposition, aluminum monostearate emits acrid smoke and irritating vapors.

Regulatory Status

Aluminum monostearate and aluminum stearate are included in the FDA Inactive Ingredients Database (oral capsules and tablets, topical creams and ointments). Included in nonparenteral medicines licensed in the UK. 17 Related Substances Aluminum distearate; aluminum tristearate. Aluminum distearate Empirical formula C36H37AlO5 Molecular weight 877.39 CAS number [300-92-5] Synonyms Hydroxyaluminum distearate; aluminum stearate; aluminum monobasic stearate. Description Aluminum distearate occurs as a fine white to offwhite colored powder with a slight odor of fatty acid. Melting point 150–1658C Specific gravity 1.01 Solubility Soluble in benzene, and in ethanol (95%); practically insoluble in water. Comments The EINECS number for aluminum distearate is 206101-8. Aluminum tristearate Empirical formula C54H105AlO6 Molecular weight 610.9 CAS number [637-12-7] Synonyms Hydroxyaluminum tristearate; aluminum stearate. Description Aluminum tristearate occurs as a fine white to offwhite colored powder with a slight odor of fatty acid. Melting point 117–1208C Specific gravity 1.01 Solubility Practically insoluble in water. Soluble in ethanol (95%), benzene, turpentine oil, and mineral oils when freshly prepared. Comments The EINECS number for aluminum tristearate is 211279-5.

Comments

A specification for aluminum stearate, described as consisting mainly of the distearate, is included in the Japanese Pharmaceutical Excipients (JPE).(4) It should be noted that aluminum stearate can also refer to the distearate (CAS number 300-92-5) and the monostearate (CAS number 7047-84-9) in addition to the tristearate (CAS number 63712-7). The distearate exhibits the same excipient properties as the tristearate and is used in similar pharmaceutical applications. However, the monostearate is more widely used in both cosmetic and pharmaceutical preparations. The EINECS number for aluminum monostearate is 230-325-5. 19 Specific References 1 Horoz BB et al. Effect of different dispersing agents on the characteristics of Eudragit microspheres prepared by a solvent evaporation method. J Microencapsul 2004; 21: 191–202. 2 Wu PC et al. Preparation and evaluation of sustained release microspheres of potassium chloride prepared with ethylcellulose. Int J Pharm 2003; 260: 115–121. 3 Wu PC et al. Design and evaluation of sustained release microspheres of potassium chloride prepared by Eudragit. Eur J Pharm Sci 2003; 19: 115–122. 4 Japan Pharmaceutical Excipients Council. Japanese Pharmaceutical Excipients 2004. Tokyo: Yakuji Nippo, 2004; 74–75. Aluminum Oxide

General References

Author

Ferro Corporation. Technical literature: Synpro Aluminum Monostearate J Shur. NF, 2008. Mallinckrodt. Technical literature: HyQual Aluminum stearate, 2008. 22 Date of Revision 19 February 2009.