Fluorine selected properties

Table 16.6 fists selected properties of Sep4, SeFg, Tep4 and TeFg. Selenium tetrafluoride is a good fluorinating agent. It is a liquid at 298 K and (compared with SF4) is relatively... 

Some Selected Properties of Hydrogen, Lithium, and Fluorine... 

Table 8.3 lists selected properties of the first four halogens. Notice that the properties of the halogens, like those of the aUcaU metals, vary fairly regularly as we proceed down the colnmn. As expected from periodic trends, the atomic radius and the density increase for each snccessive halogen. We can see from the melting and boiling points that fluorine and chlorine are both gases at room temperature, bromine is a liquid, and iodine is a solid. 

There are a number of industrial gas separation systems that use the selective permeability of plastics to separate the constituents. In design problems relating to such applications, the designer must consider the environmental conditions to determine whether the materials having the desired properties will withstand the temperatures and physical and chemical stresses of the application. Frequently the application will call for elevated temperatures and pressures. In the case of uranium separation, the extreme corrosivity of the fluorine compounds precluded the use of any material but PTFE. The PTFE... 

The development of synthetic methods for the selective introduction of short-chain perfluoroalkyl groups into organic molecules is of interest in drug development [464]. Fluoromodifications often confer unique properties on a molecule, for example in terms of increased metabolic stability and lipophilicity and, as a consequence, the pharmacokinetic profiles are often improved [465]. Burger and coworkers developed a domino process consisting of a SN reaction combined with a Claisen and a Cope rearrangement which allows the transformation of simple fluorinated compounds into more complex molecules with fluoro atoms [466]. Treatment of furan 2-917 with 2-hydroxymethyl thiophene (2-918) in the presence... 

The use of fluorine to modulate properties including potency, selectivity, pharmacokinetics, and toxicity has have been highlighted. Fluorine has also been suggested as a potential bioisosteric replacement for a number of functional groups, examples of which are presented in the final section. 

In contrast to past environmental problems associated with fluorocarbon refrigerants, the exceptional properties of fluorine in polymers have great environmental value. Some fluoropolymers are enabling green technologies such as hydrogen fuel cells for automobiles and oxygen-selective membranes for cleaner diesel combustion. 

Fluorine-containing polymers exhibit unique chemical and physical properties and high performance that are not observed with other organic polymers. They possess high thermal stability, high chemical stability, a low coefficient of friction, low adhesion, water and oil repellency, low refractive index, and outstanding electric insulation. In addition, there have recently been new expectations of selective permeability, piezoelectricity, and biocompatibility. 

Surface fluorination changes the polymer surface drastically, the most commercially significant use of polymer surface direct fluorination is the creation of barriers against hydrocarbon permeation. The effectiveness of such barriers is enormous, with reductions in permeation rates of two orders of magnitude. Applications that exploit the enhanced barrier properties of surface-fluorinated polymers include (1) Polymer containers, e.g., gas tanks in cars and trucks, which are produced mostly from high-density polyethylene, where surface fluorination is used to decrease the permeation of fuel to the atmosphere and perfume bottles. (2) Polymeric membranes, to improve selectivity commercial production of surface-fluorinated membranes has already started.13... 

Engineering thermoplastics, 10 168-228 categories of, 10 169, 170-171t chemical resistance of, 10 224, 225t considerations for selecting, 10 220-222 costs of, 10 222-223 electrical properties of, 10 223 fluorine-containing polymers,... 

Perfluorinated alkanes and cycloalkanes are prepared from the corresponding hydrocarbons, either by electrochemical fluorination or by cobalt trifluoride fluo-rination [3], Many perfluorinated solvents are available commercially covering a wide selection of boiling points and densities. Some examples of perfluorinated solvents are listed in Table 3.1 together with their key physical properties. 

General Physical Properties of Selected Fluorine-Containing Polymers... 

Table 6.7 contains physical properties of selected fluorine-containing polymers described above. 

The special advantages of selective substitution of fluorine in drug design and development are well recognized and have been reviewed extensively [21]. Small size and high electronegativity impart special properties to fluorinated... 

In Section 1.3, the general effects of fluorine substitution on drug activity and selectivity have been treated. As seen frequently with other enzymatic reactions, introduction of fluorine can have dramatic effects on the properties of substrates and inhibitors of MAOs [26]. For example, preliminary studies indicated that fluorination of 5-hydroxytryptamine in the 6- or the 4,6-positions (3,4) causes this predominantly MAO A substrate to be metabolized significantly by platelet MAO B [27]. Although no direct evidence was obtained, this may be caused by increased lipophilicity introduced by fluorine substitution. 

Inhibitors known to be selective for MAO A or B have been labeled with P F]-fluorine for PET studies. For example, [ F]-fluoroclorgyline (35) labeled on the aromatic ring with low specific activity [ F]-fluorine was shown to have favorable properties for mapping MAO A activity in the brain [103],... 

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