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Hydrocarbons (HC)

    Synonyms:(a) A-17; Aeropres 17; n-butane; E943a
    (b) A-31; Aeropres 31; E943b; 2-methylpropane
    (c) A-108; Aeropres 108; dimethylmethane; E944; propyl hydride

    Description: Hydrocarbon propellants are liquefied gases and exist as liquids at room temperature when contained under their own vapor pressure, or as gases when exposed to room temperature and atmospheric pressure. They are essentially clear, colorless, odorless liquids but may have a slight etherlike odor.

    Chemical Name: (a) Butane

    • Propane, butane, and isobutane are hydrocarbons (HC). They are used as aerosol propellants: alone, in combination with each other, and in combination with a hydrofluoroalkane (HFA) propellant.

    • They are used primarily in topical pharmaceutical aerosols (particularly aqueous foam and some spray products).

    • Depending upon the application, the concentration of hydrocarbon propellant range is 5–95% w/w.

    • Foam aerosols generally use about 4–5% w/w of a hydrocarbon propellant consisting of isobutane (84.1%) and propane (15.9%), or isobutane alone.

    • Spray-type aerosols utilize propellant concentrations of 50% w/w and higher.

    • Hydrocarbon propellants are also used in cosmetics and food products as aerosol propellants.

    • Only highly purified hydrocarbon grades can be used for pharmaceutical formulations since they may contain traces of unsaturated compounds that not only contribute a slight odor to a product but may also react with other ingredients resulting in decreased stability.

    Other than their lack of miscibility with water, butane and the other hydrocarbon propellants do not have any practical incompatibilities with the ingredients commonly used in pharmaceutical aerosol formulations. Hydrocarbon propellants are generally miscible with nonpolar materials and some semipolar compounds such as ethanol.

    The hydrocarbons are generally regarded as nontoxic materials when used as aerosol propellants. However, deliberate inhalation of aerosol products containing hydrocarbon propellants can be fatal as they will deplete oxygen in the lungs when inhaled.

    Butane and the other hydrocarbon propellants are liquefied gases and should be handled with appropriate caution. Direct contact of liquefied gas with the skin is hazardous and may result in serious cold burn injuries. Protective clothing, rubber gloves, and eye protection are recommended.

    Dimethyl ether.