Fluorine : a paradoxical element
Résumé
Last few decades, fluorine and fluorinated products have attracted significant attention, because they are greatly involved in our daily life and environment. Although many beneficial breakthroughs have been brought to us thanks to fluorine and fluoride compounds, they are decried today because of some environmental drawbacks. The goal of this book is to provide a better understanding of the many advantages, but also some disadvantages, of these products, focusing on the real place and importance of fluorine and fluorinated products in our current environment and everyday life. Of course, everyone knows that this element is present in toothpastes we use regularly, but who is really aware that it surrounds us in most instances of our life? Fluorine is not a rare element. In fact, it is the 13th most abundant element constituting the Earth's crust, where it is present at about 0.06% to a depth of 16 km. It is the second anion after oxygen. It is most found in minerals such as fluorite, apatite, topaz, and tourmalines, but also in the oceans, groundwater, lakes, and rivers. Much closer to us, it is also an essential constituent of our teeth and our skeleton, as well as those of all mammals. Finally, fluorinated molecules also exist in several plants. Unlike oxygen (O2), which is the essential constituent of our atmosphere, fluorine gas (F2) could not be found in nature until very recently, due to its high chemical reactivity. Indeed, due to its electronic structure (1s2 2s2 2p5), one electron is missing in the 2p electronic layer to complete the valence shell to eight electrons (2s2, 2p6), which corresponds to the electron configuration of the nearest noble gas, neon (octet rule). Thus, because of the reaction ½F2 + e− → F−, the element oxidizes almost all other elements, leading to generally very stable compounds in which it is present under the form of a fluoride ion, F−. However, for simplicity, the word fluorine is often used to identify the species present in a product, whatever the charge.
Physical chemical properties of fluorine will illustrate how it is certainly the most paradoxical of the elements, because the majority of its properties derive from a duality: so reactive on one hand that it could not be isolated for centuries, and on the other hand, giving most stable bonds with almost all other elements (particularly with carbon), so stable that the formed products often stay unmodified in the stratosphere. Obviously, we will discuss the contribution of the refrigerant gases containing fluorine, CFC and HCFC, to the depletion of the ozone layer, and perfluorocarbons and other perfluorinated molecules’ contribution to the greenhouse effect.
Discoveries and anecdotes about the real history of fluorinated materials throughout centuries will be illustrated using some major examples in the first section. We will present some decisive discoveries and stages of development in fluorinated products that took place during the 20th century following the isolation of fluorine by H. Moissan in 1886, with particular emphasis on the technological advances that have followed. The contributions of fluorinated products these last 50 years will be described in the second section. Issues relative to these products are of primary concern for humans in important areas such as modern technology, medicine, pharmacy, and biotechnology. Examples will be given in various fields: photonics, energy production, new drugs, surfactants, fire emulsions, TV components, fluorinated polymers, alternative materials in cardiovascular surgery, anti-decay products, and medical imaging applications. A third section will deal with the presence of fluorine and fluorinated products around us and their effect on our environment (atmosphere, lithosphere, water, gaseous emissions), focusing on efforts to limit harmful consequences. We will conclude this section on fluorine's impact on man by giving examples of different types of fluoride contaminations (water, food, industrial environmental), together with the physiological effects of fluorides on living organisms; the solutions that have been proposed to solve these problems will be also considered.
Because of the importance of this element, international meetings are regularly devoted to all fields involving Fluorine. The last International Symposium on Fluorine Chemistry was held in Oxford, UK on July 2018 and the next European one will take place in Warsaw on August 2019. It can be added that several “Fluorine Networks” have been created in various countries, including France , USA, UK, Germany, Russia and Japan, to promote activities related to fluorine in various sectors of chemistry, new technologies, life sciences, medicine and the environment. It should be noted that several specialized books have appeared in recent years dealing with many fields of fluorine chemistry and fluorinated materials: organic and inorganic compounds, fluoropolymers, pharmaceutical molecules, industrial and biomedical applications, etc. These volumes, which propose highly specialized information, are collected in a table at the end of this book. But so far, no attempt had been made to produce an English-language work with a comprehensive and global approach to this element's impact on humanity, that is, advanced technologies we use every day, the air we breathe, the water we drink, the land we live on, etc. Rather than listing tedious documents on the various classes of fluorinated products (the features and applications of which can be better found in more specialized books), it was decided that the following pages should propose an original global approach to the topic, illustrating (I hope) the importance of this element on our environment and life. The varied fields involving fluorine, such as history, cosmochemistry, global warming, radiative forcing, natural and anthropogenic emissions, the water cycle, etc., will be thus evoked, but without ignoring some negative aspects of these products. The place of fluorine and fluorinated products in key areas for our future will be also evoked, dealing with waste reduction, global warming, energy independence, microelectronics, nanotechnologies, etc.
In this book, the author wanted to show a personal version of the image of fluorine and fluorinated products, of their importance in our daily lives, as well as all the promising contributions in many fields of science and technology. However, the disadvantages caused to our health and environment by some of these products have not been underestimated. Unfortunately, the author could not consider all properties and applications of these materials, and begs concerned colleagues to excuse him in case of important omissions.
Note: In this book, the word “fluorine” may be taken either for the element or for the F2 gas (difluorine); on the other hand, the word “fluoride” may be taken either for a compound/material or the anion F−.