Fluorine is both a devil and an angel!
For humans, among the chemical elements, there is a guy who is both hateful and lovely.
It is extremely lively and mischievous, has a bad temper and is aggressive, and ordinary containers can't confine it at all, and it is also responsible for chemical weapon nerve gas.
Once its character is determined, human beings have achieved a brilliant and flourishing chemical industry.
Who is that? It is fluorine known as the "chemical superman".
Fluorine is the first element in the halogen family, and it is also the latest element discovered. In the history of chemical element discovery, the research topic with the longest duration, the largest number of participants, the greatest risk, and the most difficult work is the preparation of fluorine element. got it. It has been 76 years since Ampere pointed out that hydrofluoric acid contains a new element - fluorine, in 1810, and French chemist Moissan obtained elemental fluorine in 1886.
Fluorocarbon phase: The fluorocarbon phase can be used to extract fluorine-containing compounds in the organic phase by using the property that it is soluble in organic phase at high temperature and immiscible at low temperature. It is also possible to use a fluorine-friendly or fluorine-containing catalyst based on this characteristic. During the reaction, the fluorocarbon phase containing the catalyst and the organic substance are mutually soluble, and after the reaction is completed, the temperature is lowered so that most of the catalyst remains in the fluorocarbon phase, thereby Save catalyst consumption.
2. Fluorine-containing polymer materials
Sealing materials: High-corrosion-resistant media, high-temperature resistance, low-temperature resistance, radiation resistance, aging resistance, etc. The sealing materials include: fluorosilicone rubber, phenylene fluorosilicone rubber, and perfluoroether rubber.
Flame retardant materials: specially processed polytetrafluoroethylene powder, polyperfluoroethylene propylene.
In order to produce fluorine gas and study the properties of fluorine, many chemists have stepped forward, leaving a very tragic history for future generations. They do not hesitate to damage their own health, and even have their precious lives taken away by fluorine gas and fluoride.
Properties of fluorine
Physical properties:
Fluorine gas is a light yellow gas, the valence of fluorine is -1, the highest electronegativity of fluorine is 4.0, the ionization energy is 17.422eV, the atomic radius is small, the melting point is -219.6°C, the boiling point is -188.1°C, the density It is 1.696g/L (0°C), atomic number 9, and atomic weight 18.9984032. The element name comes from the English name of its main mineral fluorite, and it is the most active non-metallic element. Fluorine has 18 isotopes, but only fluorine-19 is stable and exists in nature. The content of fluorine in the earth's crust is 0.072%, and important minerals include fluorite and calcium fluorophosphate. Since fluorine is very active, there is no free fluorine in nature.
Chemical properties:
The compound of hydrogen and fluorine is extremely violent, and the reaction produces hydrogen fluoride. In general, oxygen does not react with fluorine, however there are two known oxyfluorides, oxygen difluoride and dioxygen difluoride. The compounds formed by halogen itself are chlorine fluoride, chlorine trifluoride, bromine trifluoride and iodine pentafluoride. Fluorine can also displace other halogens from many halogen-containing compounds. Most organic compounds react explosively with fluorine.
Fluorine and some of its compounds are toxic and highly corrosive. Hydrofluoric acid can corrode glass, while fluoride ions are permeable in human tissue. If hydrofluoric acid contacts the skin, if it is not treated in time, it can rot to the bone and cause permanent damage, and fluoride ions can combine with calcium ions to cause poisoning, and the burn of hydrofluoric acid is not easy to be detected, usually paralysis 1-2 Pain felt after hours. In case of contact with hydrofluoric acid, rinse immediately with plenty of water and apply a suspension of 20% magnesium oxide in glycerin. However, compounds such as fluorosulfonic acid and antimony pentafluoride have far stronger acidity than general strong acids such as sulfuric acid, and a specific ratio of the mixture can even decompose paraffin.
Generally, elemental fluorine gas is stored in special copper-nickel alloy steel cylinders. Functional groups such as carbonyl and hydroxyl can be directly fluorinated by using fluorine gas in organic chemistry, in which dry nitrogen doped with 5% or 10% fluorine is used.
The hydrogen on the alkanyl group can be completely or partially substituted by fluorine, and compounds completely substituted by fluorine are generally called "perfluoro compounds". Unlike hydrocarbons, because the radius of fluorine atoms is slightly larger than that of hydrogen atoms, the arrangement of fluorine atoms on the perfluorocarbon chain is slightly helical, and this type of compound has a distinctive inertness.
Generally, perfluorinated polymers are very stable, heat-resistant, cold-resistant, and corrosion-resistant, such as polytetrafluoroethylene (Teflon), which can withstand temperatures as high as 260 ° C. It does not stick to water and general organic solvents. Only fluorine and chlorine trifluoride , chlorine pentafluoride and molten alkali metals can corrode PTFE at high temperatures. The calculation of QSAR shows that in organic molecules, if the mass proportion of fluorine atoms exceeds 60%, it can show the characteristics of "perfluorinated".
Long-chain simple perfluorinated organic compounds are generally prepared from long-chain monocarboxylic acids, and the mixture of them and potassium bifluoride is electrolyzed to replace all hydrogen atoms on the chain with fluorine atoms (such as: perfluorooctanoic acid) and further synthesize other compound.
The use of fluorine
Fluorine chemical products, including fluorine-containing electronic chemicals, fluorine-containing treatment agents, fluorine-containing additives, fluorine-containing medicines, fluorine-containing pesticides, fluorine-containing dyes, fluorine-containing surfactants, fluorine-containing coatings, etc. High and low temperature, aging resistance, low friction, insulation and other excellent properties are widely used, and have become one of the fastest growing and most promising industries in the chemical industry. Its application fields have already begun to shift from traditional industries to construction, electronics, energy, and environmental protection. , information, biomedicine and other new areas of penetration.
3. Fluorinated fine chemicals
Fluorine-containing grease: fluoroether oil, fluorochloro oil, fluorobromo oil, etc., have the characteristics of large specific gravity, good viscosity temperature, oxidation resistance, aging resistance, radiation resistance, etc., used in chemical industry, electronics/semiconductor industry, automobile manufacturing industry , Oxygen industry.
Trifluoroiodomethane: As a fire extinguishing agent, it has the characteristics of high fire extinguishing efficiency, good safety performance, high economic utility, and no trace left after fire extinguishing.
Artificial blood plasma: perfluoroether compounds can carry oxygen and some nutrients and excrement needed by the human body. When a whole body exchange transfusion is needed, it can be used to temporarily replace the blood in the patient's body; due to its volatility, it can be discharged after a few days. Because perfluorinated compounds are very stable, there are generally few toxic side effects.
Fluorine-containing anesthetics: enflurane, isoflurane, sevoflurane, desflurane, etc., with less toxic and side effects, fast anesthesia onset, and short recovery time.
Chemical weapons: Fluorine-containing phosphonate compounds are extremely toxic, and the first such nerve gas, sarin, was developed; later, more toxic gases of this type, soman and VX, were discovered.
4. Fluorine isotopes
Fluorine-18 is a good source of positrons (positron emitter), often used in the synthesis of positron emission tomography (PET) tracers, currently the most commonly used clinical tracer (PET tracer) fluorine- 18-generation deoxyglucose (18F-FDG) is a tracer containing fluorine-18.