MILESTONES IN

Walter Navarrini Henri Moissan 1906 on Chemistry

WALTER NAVARRINI Politecnico di Milano Via Macinelli 7 Milano, 20131, Italy

rofessor H. Moissan made that at that time his research was considered difficult and exotic and outstanding contributions to the Moissan could not imagine the number of breakthrough innovations Pdevelopment of applied chemistry in that were going to take place one century later starting from his the late XIX and early XX century. For the pioneer studies. Before Moissan, many researchers, starting with the first time he obtained in free English G. Davy, had made unsuccessful attempts to obtain state, studied a number of fluorine fluorine. In 1886, Moissan was able to succeed were others had compounds, designed an electric failed. He isolated fluorine by of an anhydrous mixture of arc furnace and set the foundation hydrofluoric acid and potassium fluoride. The French academy of of high-temperature chemistry. science sent three representatives, M. Berthelot, H. Debray and E He synthesized many high-melting Frémy, to prove the results. At the beginning Moissan was unable to compounds and isolated and reproduce his results, due to the fact that in the repeated experiments other elements by reducing their oxides, finally did not contain any traces of the necessary he theorised and attempted the preparation of artificial potassium fluoride, as in the previous experiment. After resolving the (1). He was awarded with the Nobel Prize (1906) in recognition to the problem and demonstrating the production of fluorine several times, 4 isolation of fluorine and for his studies on high-temperature chemistry. he was awarded a prize of 10,000 francs (2, 4). He died suddenly in in February 1907, shortly after his return from The yellow-green gas obtained was highly toxic and proved to be receiving the Nobel Prize in . a powerful oxidizing agent, causing organic materials to burst into The family Moissan originated from Toulouse and moved to Paris, flames on entering into contact with it and combining directly, and where Moissan was born on September 28, 1852. In 1870 he left the often violently, with almost all other elements (5). school without the baccalaureate degree necessary to attend the From that moment on Moissan mainly committed his study to fluorine university. He wanted to be economically independent as soon as chemistry. He also contributed to the development of the electric possible, therefore started to work as apprentice pharmaceutical arc furnace and he theorised and attempted to synthesize artificial chemist in Paris, where he was able to save a person intoxicated with under pressure from the more common form of . arsenic. In this period he decided to study chemistry and started first In 1893, Moissan began studying fragments of a meteorite found in at the laboratory of Edmond Frémy and later continued at that of near Diablo Canyon in . In these fragments he Pierre Paul Dehérain. Moissan finally obtained the baccalaureate discovered minute quantities of a new mineral and, after extensive degree in 1874 (2). Moissan was an eclectic scientist and for many research; Moissan concluded that this mineral was made of years he dedicated himself to two scientific areas, pharmacy and . In 1905, this mineral was named , in his honour. experimental chemistry. He published his first scientific paper about The electric arc furnace designed by the scientist in 1892, has found and metabolism in plants with Dehérain in wide applications. It was used to obtain several metals in pure form: 1874 and was appointed a senior chemist in 1879. At this point he uranium, tungsten, vanadium, chromium, and manganese (1893); left plant physiology and turned towards inorganic chemistry and his titanium and molybdenum (1895); niobium (1901); tantalum (1902); research on pyrophoric iron was very well evaluated by the two most and thorium (1906) (1). Moissan synthesized and studied a number of prominent French inorganic of that time: H.S.C. Deville and fluorine-and carbon-containing compounds. These included carbon H.J. Debray. Moissan received his Ph.D. in 1880 and in the same year tetrafluoride, methyl fluoride, and isobutyl fluoride; in collaboration obtained a position at an analytic laboratory in Paris (3). with Paul Lebeau he synthesised SF6 (an inert gas now utilized in He had his own laboratory, but he loved most to collaborate with ultrasound imaging for medical diagnoses as well as inert gas for high many eminent colleagues and he made magisterial use of their voltage switches). Today, fluorine is still synthesized electrochemically laboratories and apparatus for specific studies, for example he using the principle elaborated by Moissan (2). One of the main uses collaborated with Frémy, Friedel, Landrine, Dehérain, Lebeau, of this process today is the transformation of uranium tetra-fluoride Meslans, Poulenc, Dewar, Becquerel and Berthelot (4). into its hexafluoride, an essential stage in the production of nuclear It is impossible to reflect in full the diversity and scale of experimental energy (3). investigations carried out by Henri Moissan. More evidence about his There are over 600 000 compounds that contain at least one atom life and scientific activities can be found in a detailed communication of fluorine, and the chemistry of fluorine and fluorine-based products by , a German scientist who worked for some time with has allowed huge breakthroughs in a wide variety of fields, including Moissan and was well-acquainted with him (3). organic chemistry (6), materials science (7), polymers (8), drugs, During the 1880s Moissan’s work was focused on fluorine chemistry and medical applications (9). Some of the great discoveries that and especially on the production of fluorine itself. It should be noted emerged in the 20th century include: Energy-conversion processes

chimica oggi/Chemistry Today - vol. 29 n. 3 May/June 2011 MILESTONES IN CHEMISTRY

(e.g. in Li ion batteries, fuel cells, and nuclear energy). Fluoropolymers such as Teflon, anti-stick and resist corrosion material (8). Fluorine and fluoride etching gasses in microelectronics within the micro lithography production process of silicon core components for personal computers. Fluoro-surfactants to protect fabrics, carpets, and leather, and as a fire-retardant material. Fluorinated general anesthetics (Sevoflurane) and fluorinated anti-cancer drugs (Fluorouracil). Fluorinated molecules as anti-inflammatory, antibiotics, antihypertensive drugs. Perfluorocarbons in vitreoretinal surgery and as blood substitutes for emergency transfusions (9). Fluorinated molecules containing one or several atoms of fluorine as efficient herbicides, fungicides, or insecticides. 18F positron emission tomography or 19F NMR for medical imaging to detect the early presence of tumours and for diagnosing brain diseases such as Alzheimer. These really remarkable discoveries indirectly determine some of the recent environmental constraints: ground water fluoride contamination in specific geographic areas, ozone depletion layer, global warming, which more recently have Figure 2. Moissan’s Nobel Prize diploma and the electrolytic cell used for producing fluorine (3). resulted in the withdrawal of some useful but persistent and bio accumulative perfluorinated materials, such as PFOS and of industrial research. In the area of medical chemistry it is a tangible PFOA (10). Some of these reality with about 20-25 percent of commercial drugs containing important limitations are due at least one fluorine atom (9, 13). Fluorine chemistry, also thanks to the carbon-fluorine bond to Moissan’s pioneer work is an attractive frontier science, it arises that is essentially xenobiotic between organic and inorganic chemistry and has been often and has an extremely high considered a self-standing branch of chemistry as well as advanced stability, therefore fluorinated material science constantly able to give important scientific answers molecules are often resistant to almost any industrial application. to degradation, representing To commemorate Moissan’s isolation of elemental fluorine in 1886 a potential environmental and to stimulate research in the fields of fluorine chemistry in 1986, challenge. Strategic research in occasion of the centenary of the discovery of fluorine the “Henri is on-going in industry and Moissan International Prize” was created. academia worldwide to During the last twenty-four years the prestigious Moissan award provide viable solutions to was attributed every three years in occasion of the International these key environmental Symposium of Fluorine Chemistry (ISFC). The eight distinguished 5 challenges (11). Considering fluorine chemists (Bartlett 1988, Emeleus 1991, Haszeldine 1994, Figure 1. Henri Moissan (1852-1907). the number and the Hagenmuller 1997, Christe 2000, Chambers 2003, DesMarteau 2006, relevance of industrial Roesky 2009) who have been awarded with this prestigious prize are applications based on fluorinated compounds and fluorinated the proof of the living heredity of Henry Moissan. materials the definition of “A little atom with an enormous ego” coined few years ago is full of significance. We have to acknowledge the little and aggressive fluorine starting REFERENCES AND NOTES from the early days at the beginning of the century has definitively grown up with countless applications in any scientific and industrial 1. Russian Journal of Applied Chemistry, 75(10), pp. 1720-1722 (2002). field. Fluorine is definitively unique and confers distinctive molecular 2. Fluorine the First Hundred Years (1886-1986), Editors: R.E.Banks, D.W.A. properties to many fluorine containing compounds studied for Sharp and J.C.Tatlow, Elsevier Sequoia new York Chapter 2 p. 27-42 relevant developments. Today the chemical reactivity of fluorinated 3. A. Tressaud, Angew. Chem. Int., Ed., 45, pp. 6792-6796 (2006). compounds is rather well understood and fairly predictable. The 4. Wikipedia on line International Encyclopedia “Henri Moissan Nobel Prize factors determining the multiple unique properties of fluorine can be on Chemistry” summarized as high electronegativity, small size, low polarizability, 5. a) E. Banks, J. Fluorine Chem., 33, p. 3-26 (1986); b) Fluorine Chemistry excellent orbital overlap with second period elements, strong bond at the Millennium: Fascinated by Fluorine (Ed.: R. E. Banks), Elsevier, between carbon and fluorine, tightly non-bonding electrons, and Dordrecht (2000). shielding of the carbonbackbone by fluorine atoms (12). Serendipity is 6. a) K. Uneyama, Organofluorine Chemistry, Blackwell, Malden, USA (2006); quite frequent in any complex scientific areas and fluorine chemistry, b) R. Chambers, Fluorine in Organic Chemistry, Blackwell, Malden, USA is not an exception to this rule, indeed it is possible to replace any (2004); c) R.E. Banks, B.E. Smart et al., Organofluorine Chemistry: Principles hydrogen in an organic molecule or macromolecule with fluorine & Commercial Applications, Kluwer/Plenum, New York (1994). atom, creating an infinite extension of completely synthetic organic 7. T. Nakajima, B. Zemva et al., Advanced Inorganic Fluorides: Synthesis, chemistry, since very few compounds containing carbon-fluorine Characterization and Applications, Elsevier, Dordrecht (2000). bonds are present in nature. 8. B. Ameduri, B. Boutevin, Well-Architectured Fluoropolymers, Elsevier, Indeed the high number of bioactive compounds derive from Dordrecht (2004). the intense structure-activity relationship rather than by rationale 9. J.P. Bégué, D. Bonnet-Delpon, Chimie Bioorganique et Médicinale du prediction, with the important exception of the increase in metabolic Fluor, EDP-Sciences, Paris (2005). stability very often obtained by fluorine substitution (13). This magic 10. Fluorine and the Environment, 1; Atmospheric Chemistry, Emissions dance between comprehension and destiny is the playground & Lithosphere Agrochemical, 2, agrochemical, archaeology, green of our “little fluorine”, and we are back to a rejuvenation period, Chemistry& Green Chemistry, Edited by Alain Tressaud (2006) Elsevier. carrying new perspectives, very high activity and productivity. 11. Chimica Oggi/Chemistry Today, 24(3), p. 3, Focus on Fluorine chemistry. Fluorine organic chemistry applied to medicinal chemistry and 12. B.E. Smart, Journal of Fluorine Chemistry, 3, p.109 (2001). agrochemical areas has in fact only recently gained the attention 13. C. Isanbor, DO’Hagan, Journal of Fluorine Chemistry, 127, p. 303 (2006).

chimica oggi/Chemistry Today - vol. 29 n. 3 May/June 2011