Teflon chemistry

Many fluorides are corrosive to glass and some metals Even the very corrosive anhydrous fluorides, however, can be handled at room temperature in steel, stainless steel, copper, and Teflon equipment For reactions at higher temperature, nickel and Monel metal are indispensable More data on corrosion of matenals are given in pages 22 and 23 of Chemistry of Organic Fluorine Cowjpoundi, published in 1676... 

Capillary electrophoretic separations are performed in small diameter tubes, made of Teflon, polyethylene, and other materials. The most frequently used material is fused silica. Fused silica capillaries are relatively inexpensive and are available in different internal and external diameters. An important advantage of a fused silica capillary is that the inner surface can be modified easily by either chemical or physical means. The chemistry of the silica surface is well established due to the popularity of silica surfaces in gas chromatography (GC) and liquid chromatography (LC). In capillary electrophoresis, the silica surface is responsible for the EOF. Using surface modification techniques, the zeta potential and correspondingly the EOF can be varied or eliminated. Column fabrication has been done on microchips.13... 

Figure 8 High throughput organic synthesizer developed in collaboration with Cyberlab, Inc. [25] and designed to process the 96-deepwell reaction blocks. The instrument is capable of tolerating a wide range of chemistry (liquid contacts are glass, stainless steel, or Teflon) and accomplishes the transfer of reagents with coaxial tip (N2 inlets) single-needle and four-needle probes.

FIGURE 16.6 Schematic of the clear flow gating interface. The interface was constructed in-house from a 1 in. diameter, 0.5 in. thick Lexan disk. The disk is clear, which allows direct observation of the capillaries in the stream of flush buffer. The capillaries are sleeved in 0.0625 in. o.d. Teflon tubing and this tubing is held in place by Lite Touch fittings (not shown). The cross-flow of buffer prevents LC effluent from electromigrating onto the CZE capillary until an injection is desired (reprinted with permission from Analytical Chemistry). 

CombiCHEM System (Fig. 3.9) For small-scale combinatorial chemistry applications, this barrel-type rotor is available. It can hold two 24- to 96-well microtiter plates utilizing glass vials (0.5-4 mL) at up to 4 bar at 150 °C. The plates are made of Weflon (graphite-doped Teflon) to ensure uniform heating and are sealed by an inert membrane sheet. Axial rotation of the rotor tumbles the microwell plates to admix the individual samples. Temperature measurement is achieved by means of a fiber-optic probe immersed in the center of the rotor. 

Reaction scale-up using the Voyager system in genuine continuous-flow format is achieved by the use of special coiled flow-through cells. The reaction coils are made of glass or Teflon (Fig. 3.24) with a maximum flow rate of 20 mL min-1 and operational limits of 250 °C or 17 bar. The continuous-flow format should only be used for homogeneous solution-phase chemistry, as slurried mixtures may cause prob-... 

Since the serendipitous discovery of Teflon at the Dupont Jackson Laboratory in 1938, fluoropolymers have grown steadily in technological and marketplace importance. New synthetic fluorine chemistry, new processes, and new appreciation of the mechanisms by which fluorine imparts exceptional properties all contribute to accelerating growth in fluoropolymers. 

All four dissolution procedures studied were found to be suitable for arsenic determinations in biological marine samples, but only one (potassium hydroxide fusion) yielded accurate results for antimony in marine sediments and only two (sodium hydroxide fusion or a nitricperchloric-hydrofluoric acid digestion in sealed Teflon vessels) were appropriate for determination of selenium in marine sediments. Thus, the development of a single procedure for the simultaneous determination of arsenic, antimony and selenium (and perhaps other hydride-forming elements) in marine materials by hydride generation inductively coupled plasma atomic emission spectrometry requires careful consideration not only of the oxidation-reduction chemistry of these elements and its influence on the hydride generation process but also of the chemistry of dissolution of these elements. 

The next stage of development went to polymer chemists and development engineers, as the expertise of Roy Plunkett was really in fluorine chemistry. The first great application was in the separation of the isotope U-235 from U-238 by gaseous diffusion of UFe to make atomic bombs, as the gas uranium hexafluoride was exceedingly corrosive and destroyed conventional gaskets and seals. PTFE was just what was needed to form the diffusion membrane, as it was not attacked by fluorine. When peace returned, PTFE registered the trademark of Teflon in 1944. 

Some powerful companies, such as Dupont de Nemours, took advantage of these new possibihties in inorganic chemistry and in the field of polymers. Indeed, new materials with exceptional properties were developed, and some fluorinated polymers are now famous under their trademark names (e.g.. Teflon , GoreTex ). 

Another unique development, which significantly reduced the amount of reagent necessary for an assay, is an extension of the continuous-flow analyzer technology called capsule chemistry. The core of die system is a capillary Teflon tube coated on the inside with a thin, flowing film of... 

Molten salts or ionic liquids (also referred to as fused salts by some authors) were among the very first media to be employed for electrochemistry. In fact, Sir Humphrey Davy describes electrochemical experiments with molten caustic potash (KOH) and caustic soda (NaOH) [1] as early as 1802 A wide variety of single molten salts and molten salt mixtures have been used as solvents for electroanalytical chemistry. These melts run the gamut from those that are liquid well below room temperature to those melting at more than 2000°C. The former present relatively few experimental challenges, whereas the latter can present enormous difficulties. For example, commercially available Teflon- and Kel-F-shrouded disk electrodes and Pyrex glass cells may be perfectly adequate for electrochemical measurements in ambient temperature melts such as the room-temperature chloroaluminates, but completely inadequate for use with molten sodium fluoroaluminate or cryolite (mp = 1010°C), which is the primary solvent used in the Hall-Heroult process for aluminum electrowinning. 

SH Chiou, Wang KT. A rapid and novel means of protein hydrolysis by microwave irradiation using Teflon-Pyrex tubes. In Current Research in Protein Chemistry. San Diego Academic Press, 1990, pp 3-10. 

Fig. 4. Monomode microwave reactor with integrated robotic platform for automated use (left). A liquid handler allows dispensing of reagents into Teflon-sealed reaction vials, while a gripper moves each vial in and out of the microwave cavity after irradiation. The instrument processes up to 120 reactions per run with a maximum throughput of 12-15 reactions/h. The temperature is measured by an IR sensor on the outside of the reaction vessel. Details of the cavity/gripper (top right) and reaction vials (bottom right) are also displayed (Emrys Synthesizer, Personal Chemistry AB). Reprinted with permission from Wiley-VCH.41 (See color insert.)...

Macromolecular chemistry covers a particularly wide field which includes natural polymeric material, such as proteins, cellulose, gums and natural rubber industrial derivatives of natural polymers, such as sodium carboxymethyl cellulose, rayon and vulcanised rubber and the purely synthetic polymers, such as polythene (polyethylene), Teflon (polytetrafluoroethylene), polystyrene, Perspex (poly (methyl... 

The Arizona State University Chemistry Department, under contract to the BWIP, has designed a H2 diffusion membrane consisting of a 3-in.-long,l/4-in.-OD, closed-end Teflon tube with a wall thickness of 0.03 in. The mechanical strength of the membrane has been tested to 260°C and 1,500 bars and was able to hold pressure and pass H2 under these conditions. 

A more recently published example of organic microwave synthesis under CF conditions is the 1,3-dipolar cycloaddition chemistry in the CEM CF Voyager system (Fig. 11). Savin and coworkers presented the cycloaddition of dimethyl acetylene dicarboxylate with benzyl azide in toluene, which was first carefully optimized with respect to solvent, temperature, and time under batch conditions. The best protocol was then translated to a CF procedure where a 0.33 M solution of both building blocks was pumped through a Kevlar-enforced Teflon coil (10 mL total capacity) heated in the single-mode reactor at 110 °C (10 min residence time) [66]. This method provided a 91% conversion to the desired triazole product (Scheme 12). 

---