1,1-Difluoroethane

Production

1,1-Difluoroethane is a synthetic substance that is produced by the mercury-catalyzed addition of hydrogen fluoride to acetylene: :HCCH + 2 HF → CHCHF The intermediate in this process is vinyl fluoride (C2H3F), the monomeric precursor to polyvinyl fluoride.

Uses

With a relatively low global warming potential (GWP) index of 124 and favorable thermophysical properties, 1,1-difluoroethane has been proposed as an environmentally friendly alternative to R134a. Despite its flammability, R152a also presents operating pressures and volumetric cooling capacity (VCC) similar to R134a, so it can be used in large chillers or in more particular applications like heat pipe finned heat exchangers.

In addition, 1,1-difluoroethane is also commonly used in gas dusters and numerous other retail aerosol products, particularly those subject to stringent volatile organic compound (VOC) requirements.

The molecular weight of difluoroethane is 66, making it a useful and convenient tool for detecting vacuum leaks in gas chromatography–mass spectrometry (GC-MS) systems. The cheap and freely available gas has a molecular weight and fragmentation pattern (base peak at m/z = 51 in typical EI-MS, major peak at m/z = 65) distinct from anything in air. If mass peaks corresponding to 1,1-difluoroethane are observed immediately after spraying a suspect leak point, leaks may be identified.

Safety

Difluoroethane is an extremely flammable gas, which decomposes rapidly on heating or burning, producing toxic and irritating fumes, including hydrogen fluoride and carbon monoxide.

In a DuPont study, rats were exposed to up to 25,000 ppm (67,485 mg/m) for six hours daily, five days a week for two years. This has become the no-observed-adverse-effect level for this substance. Prolonged exposure to 1,1-difluoroethane has been linked in humans to the development of coronary disease and angina. Repeated or sufficiently high levels of exposure, particularly purposeful inhalation, can precipitate fatal cardiac arrhythmia.

Abuse

Difluoroethane is an intoxicant with abuse potential. It appears to act primarily through GABAA and glutamate receptors. Fatalities linked to difluoroethane abuse include actress Skye McCole Bartusiak, singer Aaron Carter and wrestler Mike Bell. Bitterants, added voluntarily to some brands to deter purposeful inhalation, are often not legally required; they do not negate or counteract difluoroethane's intoxicating effects.

Environmental abundance

Most production, use, and emissions of HFC-152a have occurred within Earth's more industrialized and populated northern hemisphere following the substance's introduction in the 1990s. Its concentration in the northern troposphere reached an annual average of about 10 parts per trillion by year 2011. The concentration of HFC-152a in the southern troposphere is about 50% lower due to its removal rate (i.e. lifetime) of about 1.5 years being similar in magnitude to the global atmospheric mixing time of one to two years.

References

References

1. [http://www.sigmaaldrich.com/catalog/search/ProductDetail/ALDRICH/295264 1,1-Difluoroethane] at [[Sigma-Aldrich]]
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