Study of 2-H-Heptafluoropropane and Its Thermal Decomposition Using UV Photoelectron Spectroscopy and ab Initio Molecular Orbital Calculations

Asthma onset after exposure to fluorinated hydrocarbons in the presence of combustion

Fluorinated hydrocarbons, which can thermally degrade into toxic hydrofluoric acid, are widely used as, for example, cooling agents in refrigerators and air conditioning systems and as medical aerosol propellants. Hydrofluoric acid is a known causative agent of irritant-induced asthma. We report on two patients with asthma initiation shortly after exposure to fluorinated hydrocarbon-based cooling agents while welding or smoking cigarettes in a confined space. Both cases developed respiratory symptoms and headache and later demonstrated nonspecific bronchial hyperresponsiveness. In follow-up, asthma was persistent and responded poorly to asthma medication. Exposure to the fluorinated hydrocarbons themselves is unlikely to have caused asthma due to their low toxicity. Instead, exposure to small amounts of hydrofluoric acid via the thermal degradation of the fluorinated hydrocarbons was considered the most likely cause of asthma onset. This is supported by the typical clinical picture of irritant-induced asthma and acute symptoms resembling hydrofluoric acid poisoning. When fluorinated hydrocarbons are used in the presence of combustion, thermal degradation may lead to the formation of hydrofluoric acid. In confined spaces, this exposure may induce asthma via irritation. Welding, smoking, and other sources of combustion in confined spaces may be a risk in workplaces and other places in which fluorinated hydrocarbons are used.

Unimolecular rate constant and threshold energy for the HF elimination from chemically activated CF3CHFCF3

Combination of CF(3)CHF and CF(3) radicals at room temperature generated chemically activated CF(3)CHFCF(3) molecules with 95 +/- 3 kcal/mol of internal energy that decompose by loss of HF, initially attached to adjacent carbons, with an experimental unimolecular rate constant of (4.5 +/- 1.1) x 10(2) s(-1). Density functional theory was used to model the unimolecular rate constant for HF elimination, k(HF), to determine a threshold energy of 75 +/- 2 kcal/mol.