FLUORINE CHEMISTRY

VLADIMIR V. GRUSHIN

Institute of Chemical Research of Catalonia (ICIQ - Institut Català d'Investigació Química) Avgda. Països Catalans 16, 43007, Tarragona, Spain

Fluoroform as a feedstock for high-value fluorochemicals: novel trends and recent developments

KEYWORDS: fluoroform; HFC-23, trifluoromethylation, transition metal reagents and catalysts, organofluorine compounds.

Trifluoromethylated building blocks and intermediates are in exceptionally high demand for the synthesis of Abstractagrochemicals, pharmaceuticals, and specialty materials. Readily available, nontoxic and ozone-friendly fluoroform (CHF3, trifluoromethane, HFC-23), a side-product of Teflon manufacturing and a potent greenhouse gas, would be by far the best CF3 source for a variety of trifluoromethylation reactions. Chemoselective activation of fluoroform, however, is highly challenging. This article provides an overview of synthetic methods employing fluoroform with emphasis on new trends and most recent, promising developments in the area.

INTRODUCTION acids are not effective. Even in bright sunlight, there is no reaction with bromine; with chlorine, in bright sunlight, and in

In its April 3, 1890 issue, the Nature magazine highlighted (1) a quartz vessel, the hydrogen is replaced slowly to yield CF3Cl. two papers on the same subject presented at the then most With fluorine a vigorous reaction occurs, but without recent meeting of the Chemical Society of Paris. The topic carbonization, and yields carbon tetrafluoride and hydrogen was the isolation of fluoroform, CHF3, the last member of the fluoride... With regard to the physiological effect, it is sufficient haloform family to be discovered, by Chabrié and Meslans. to state that exposure of a guinea pig for one hour to a

Both scientists had prepared and isolated fluoroform from the 50-50% mixture of CHF3 and air by volume caused no effect reactions of chloroform or iodoform with silver fluoride, whatsoever. The animal was not apparently aware of the determined its density, and probed its alkaline hydrolysis (1-4). presence of the gas. In a second experiment, a guinea pig Since then, however, fluoroform had remained an exotic and was maintained in an “artificial atmosphere” of 80 volumes of virtually unstudied compound for over 40 years (5) until in the fluoroform and 20 volumes of oxygen for one hour, and again mid-1930s Ruff (6) and Henne (7) developed the synthesis of did not exhibit any symptoms of discomfort, though it was fluoroform from HgF and CHI3 or CHF2Br, respectively. These patiently aware of unusual conditions, at the start of the methods enabled, for the first time, the preparation of pure experiment” (7). fluoroform in sufficient quantities for thorough reactivity and biological activity studies. The results of those studies by In April 1938, one year after Henne’s report (7) on fluoroform Henne led him to identify fluoroform as a “substance from the Ohio State University, a recent PhD graduate of the characterized by exceptional physiological and chemical same university, 27-year-old Roy Plunkett, made one of the inertness” (7). In his 1937 report, Henne wrote: most important and fascinating discoveries of the 20th century. While researching new refrigerants at Kinetic “Fluoroform is characterized by its great stability, and almost Chemicals Inc., a joint venture between DuPont and Frigidaire complete chemical as well as physiological inertness. White (General Motors), Plunkett and his technician J. Rebok hot silica decomposes it very slowly, though completely, thus accidentally discovered polytetrafluoroethylene (8, 9), making it possible to analyze it by means of the method currently widely known under the DuPont trademark of previously recommended, and determining its molecular Teflon®. This groundbreaking finding marked the birth of weight at the same time (assuming that it behaves as a fluoropolymer chemistry (10), a new field of science that, in 75 perfect gas). Decomposition by calcium oxide is also slow, years of its existence, has brought numerous previously and proceeds only at elevated temperature (red hot), where unimaginable benefits into almost all aspects of human life. it is complete. Metals are indifferent to it. Caustic solutions, Applications of Teflon® and other fluoropolymers span a even at the boiling point, are without effect. Concentrated broad range from high-performance materials for the nuclear

Chimica Oggi - Chemistry Today - vol. 32(3) May/June 2014 81