9
Trifuoroacetic Acid from CFC
Replacements: An Atmospheric Toxicant
Becomes a Terrestrial Problem
9.1 Introduction
Our research on methyl bromide, a stratospheric ozone depleter, attracted
the attention of the Alternative Fluorocarbons Environmental Acceptability
Study (AFEAS), a consortium of chemical companies (Dupont, Imperial
Chemical Industries (ICI), and others) with a common interest of developing alternatives to the chlorofuorocarbon (CFC) refrigerants and propellants.
The CFCs depleted the stratospheric ozone layer which protects earth from
higher energy ultra-violet light. They were also greenhouse gases that keep
the atmosphere from radiating excess heat from the atmosphere to the stratosphere, and thus causing a rise in the earth’s temperature leading to global
warming. The CFCs were banned under an international agreement known
as the Montreal Protocol. The primary greenhouse gas is CO 2 , and nations
are struggling to reduce CO 2 emissions with limited success. CFCs were
GHGs that could be controlled, so most nations signed on to the Montreal
Protocol as a frst step in controlling global warming.
The AFEAS consortium sought to replace CFCs with other fuorocarbons that could be used in air conditioners, refrigerators, etc., but were not
themselves “greenhouse gases.” After much research and development, the
replacement chemicals advanced by AFEAS were the hydrochlorofuorocarbons (HCFCs), such as CF 3 CHFCl (Figure 9.1). The presence of the C−H bond
in these HCFCs allowed the HCFCs to degrade in the troposphere, and not
reach the stratosphere, and thus not deplete naturally occurring ozone in the
stratosphere. The earth would not warm irreversibly and life could continue.
But the HCFCs had a drawback: when they degrade in the atmosphere,
the major product is trifuoroacetic acid (TFA). Although not very toxic, TFA
is unusually stable and water soluble; TFA can build up in earth’s waters
that undergo evaporation to potentially harmful levels. AFEAS funded our
group at University of Nevada, Reno, and University of California, Davis, to
DOI: 10.1201/9781003217602-9
147
Trifuoroacetic Acid from CFC
Replacements: An Atmospheric Toxicant
Becomes a Terrestrial Problem
9.1 Introduction
Our research on methyl bromide, a stratospheric ozone depleter, attracted
the attention of the Alternative Fluorocarbons Environmental Acceptability
Study (AFEAS), a consortium of chemical companies (Dupont, Imperial
Chemical Industries (ICI), and others) with a common interest of developing alternatives to the chlorofuorocarbon (CFC) refrigerants and propellants.
The CFCs depleted the stratospheric ozone layer which protects earth from
higher energy ultra-violet light. They were also greenhouse gases that keep
the atmosphere from radiating excess heat from the atmosphere to the stratosphere, and thus causing a rise in the earth’s temperature leading to global
warming. The CFCs were banned under an international agreement known
as the Montreal Protocol. The primary greenhouse gas is CO 2 , and nations
are struggling to reduce CO 2 emissions with limited success. CFCs were
GHGs that could be controlled, so most nations signed on to the Montreal
Protocol as a frst step in controlling global warming.
The AFEAS consortium sought to replace CFCs with other fuorocarbons that could be used in air conditioners, refrigerators, etc., but were not
themselves “greenhouse gases.” After much research and development, the
replacement chemicals advanced by AFEAS were the hydrochlorofuorocarbons (HCFCs), such as CF 3 CHFCl (Figure 9.1). The presence of the C−H bond
in these HCFCs allowed the HCFCs to degrade in the troposphere, and not
reach the stratosphere, and thus not deplete naturally occurring ozone in the
stratosphere. The earth would not warm irreversibly and life could continue.
But the HCFCs had a drawback: when they degrade in the atmosphere,
the major product is trifuoroacetic acid (TFA). Although not very toxic, TFA
is unusually stable and water soluble; TFA can build up in earth’s waters
that undergo evaporation to potentially harmful levels. AFEAS funded our
group at University of Nevada, Reno, and University of California, Davis, to
DOI: 10.1201/9781003217602-9
147