Chlorofluorocarbons as propellants

Many years ago, the USA agreed with other comitries to stop using CECs (chlorofluorocarbons) as propellants in aerosols because they contribute to the destruction of the atmospheric ozone layer. Until recently, formulary exemptions were made for inhalers that contained CECs. The pMDI remains the most popular type of inhaler used by people with asthma, with a different propellant called hydrofluo-roalkane (HEA), also referred to as CFC-free propellant. It may be less powerful and have a different taste which could impair compliance and efficacy in children accustomed to using their old inhaler. The DPI is the... 

The production of chlorofluoro- and hydrochlorofluorocarbons expanded rapidly after 1945, reaching about 1 milbon tons in 1986 despite a drop m production in the late 1970s, when the United States and several other countnes banned the use of chlorofluorocarbons as aerosol propellants In the early 1990s, production and consumpaon are in decline... 

OTS has focused its control efforts on two other chemicals in addition to PCBs. Working in conjunction with the Food and Drug Administration, EPA used TSCA s Section 6 to prohibit the use of chlorofluorocarbons (CFCs) as propellants in nonessential aerosol products. An advanced notice of proposed rulemaking under TSCA outlined approaches for restricting other uses of CFCs, but the attempt to deal with other CFC uses has been abandoned by the Reagan Administration. 

Chlorofluorocarbons (CFCs) come in many forms, including those used as propellants for spray cans and for refrigeration (freon). They were banned as being potentially harmful to the ozone layer of the atmosphere. In 1987 an international agreement was signed by about 90 nations to reduce the use of CFCs by 50% by the year 2000. This did not seem adequate, so in 1990 a new treaty called for the elimination of the use of all CFCs by industrial nations. Some third world countries (e.g., China, India, Russia, and Mexico) still make and sell CFCs, some of which are smuggled into the United States. 

Specific bans on chemicals or uses have not been the most important outcome of TSCA. Only one type of chemical, PCBs, was specifically targeted in the original law and they are now outlawed in most of their uses. EPA administration of the law in its early years led to a ban of chlorofluorocarbons as aerosol propellants, restrictions on dioxin waste disposal, rules on asbestos use, and testing rules on chlorinated solvents. It has led to a central bank of information on existing commercial chemicals, procedures for further testing of hazardous chemicals, and detailed permit requirements for submission of proposed new commercial chemicals. 

In 1985 large holes were discovered in the ozone layer over Antarctica, Australasia and Europe (Figure 7.12). Scientists think that these holes have partly been produced by chemicals called chlorofluorocarbons or CFCs. CFCs were developed as refrigerants in fridges back in the 1950s. They have also been used in air conditioning systems, in aerosol cans (as propellants) and in the manufacture of expanded plastics such as polystyrene. CFCs are very unreactive molecules. They escape into the atmosphere and, because of their inertness, remain without further reaction until they reach the... 

Chlorofluorocarbons (CFCs) such as freons (e.g., CCI2F2 and CCI3F) were traditionally used as propellants for different liquids and as refrigerants. Fortunately, their use has decreased dramatically owing to increased awareness of their negative effect on our planet s protective ozone layer (see Section 8.4.1.5). Formaldehyde is used in the conservation of organs and in polymer preparation. It is toxic and its high vapor pressure makes it rather volatile. 

We like to use refrigeratory but until recently many models used CFCs (chlorofluorocarbons) as coolants. Aerosols and spray cans also used CFCs as propellants. As CFCs can destroy the ozone layer they have recently been replaced by more ozone friendly propellants. 

Pharmaceutical inhalation aerosols are widely used for treatment of diseases such as asthma and chronic bronchitis. There are three basic types of aerosol products the propellant-driven metered-dose inhalers, the dry powder inhalers, and the nebulizers. Because of the ozone-depleting and greenhouse effects of the chlorofluorocarbon (CFG) propellants, interest in the dry powder aerosols has risen in recent years. 

The first MDI products were developed by Riker Laboratories and marketed in 1956, using a newly patented design of metering valve. In most countries the MDI is now established as the principal dosage form of inhalation drug therapy for bronchial asthma and chronic obstructive pulmonary disease (COPD). Since its introduction, MDI technology has evolved steadily. However, with the phase-out in the commercial use of chlorofluorocarbon (CFC) propellants, which have been the mainstay of pharmaceutical MDIs, the pace of MDI technology development has accelerated with the transition to hydrofluorocarbon (HFC) propellants. ... 

Until recently, only three chlorofluorocarbon (CFC) propellants, namely CFCs 11, 12 and 114 (Table 1), had been approved worldwide for use in medical MDIs. Their widespread acceptance was due to their ability to substantially meet the ideal propellant properties. All the CFC MDIs that are currently marketed employ CFC 12 as the major constituent mixed with either CFC 11 or with a mixture of CFC 11 and CFC 114. These mixtures of propellants closely obey Raoult s law and therefore the blend selected can be used to give a defined vapor pressure (Table 1). The inclusion of CFC 11 in the formulation also offered advantages in that it increased the solvency of most propellant systems, thereby facilitating the dissolution of surfactants in suspension formulations. By virtue of it being a liquid below 24° C, it was used as the primary dispersion medium for either suspending or dissolving the drug. 

Chlorofluorocarbons (CFCs) A family of chemical compounds once used as propellants in commercial sprays but now regulated because of their harmful environmental effects. 

In the USA, the Environmental Protection Agency (EPA) additionally requires the following information on all aerosols containing chlorofluorocarbons as the propellant ... 

It is important to know whether molecules being released in the lower atmosphere can reach the stratosphere and affect the amount of ozone in it. Certain types of air pollution give rise to radicals that catalyze ozone depletion. A radical is a chemical species that contains an odd (unpaired) electron, and it is usually formed by the rupture of a covalent bond to form a pair of neutral species. One pressing concern involves chlorofluorocarbons (CFCs)—compounds of chlorine, fluorine, and carbon used as refrigerants and as propellants in some aerosol sprays. CFCs are nonreactive at sea level but can photodissociate in the stratosphere ... 

A carbon atom can be bonded to as many as four halogen atoms, so an enormous number of organic halides can exist. Completely fluorinated compounds are known as fluorocarbons or sometimes perfluorocarbons. The fluorocarbons are even less reactive than hydrocarbons. Saturated compounds in which all H atoms have been replaced by some combination of Cl and F atoms are called chlorofluorocarbons or sometimes freons. These compounds were widely used as refrigerants and as propellants in aerosol cans. However, the release of chlorofluorocarbons into the atmosphere has been shown to be quite damaging to the earth s ozone layer. Since January 1978, the use of chlorofluorocarbons in aerosol cans in the United States has been banned, and efforts to develop both controls for existing chlorofluorocarbons and suitable replacements continue. The production and sale of freons have been banned in many countries. 

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