Teflon valves

B - Switching Valve, Valeo 1/8" Fittings E - Shut-Off Valve, Teflon... 

DMAC is a good solvent for many resins therefore, flange gaskets and pump and valve packing should be limited to Teflon fluorocarbon resins. 

Eig. 6. Schematic ofTeclmicon CHEAl I analy2er where P = aspiration AIV = metering valves CT = capillary Teflon tube M = reagent mixing zone ... 

New materials also emerged. Nylon, developed brilliantly by W. H. Carothers and his team of research workers for Du Pont as a fibre in the mid-1930s, was first used as a moulding material in 1941. Also in 1941 a patent taken out by Kinetic Chemical Inc. described how R. J. Plunkett had first discovered polytetrafluoroethylene. This happened when, on one occasion, it was found that on opening the valve of a supposedly full cylinder of the gas tetrafluoroethylene no gas issued out. On subsequently cutting up the cylinder it was found that a white solid, polytetrafluoroethylene (PTFE), had been deposited on the inner walls of the cylinder. The process was developed by Du Pont and, in 1943, a pilot plant to produce their product Teflon came on stream. 

Today, the glassware required consists of either a round-bottom flask or a Schlenk tube serving as the reaction chamber. This chamber is equipped with a magnetic stirbar and a Teflon high-vacuum valve (or glass stopcock) which provides for easy vacuum control after attachment to a vacuum line (Fig. 8.7). 

To a mixture of 1,3-dibromobenzene (4.36 g, 18.49 mmol), 1,3-phenylene diamine 111 (2.00 g, 18.49 mmol), NaO-t-Bu (3.73 g, 38.84 mmol), Pd2(dba)3 (0.339 g, 0.37 mmol), and BINAP (0.691 g, 1.11 mmol) in a heavy-walled flask equipped with a Teflon valve was added THF (15 mL) under inert atmosphere. The flask was sealed and heated to 90°C. After 24 h, die reaction mixture was cooled to room temperature and neutralized using 0.2 mol equivalents of 2.4 N HC1 in MeOH. The polymer was precipitated from hexanes, filtered, and dried under vacuum. The dried polymer was redissolved in THF, filtered through Celite, and reprecipitated. The solid was collected by filtration and dien purified by Soxlilet extraction with CH2C12 overnight. After drying under vacuum, a green-tan solid was obtain in 106% yield. GPC (NMP, polystyrene standards) Mw = 39,000 ... 

Irradiation Procedure. Reaction mixtures were prepared at room temperature by transferring desired quantities of reactants from their storage bulbs to the reaction vessel, a 500-cc. spherical borosilicate glass flask attached to the vacuum line by a section of glass capillary tubing and a 4-mm. bore threaded glass valve with a Teflon plug (Fischer and Porter 795-609). Prior to each experiment this vessel was baked under vacuum at 500°C. for 12 or more hours. 

Equipment, The reactor was 1.523 liter, 316 stainless steel cylindrical, jacketed vessel equipped with two multiblade, paddle-type agitators. Tracer studies showed the reactor was well-mixed. A thermocouple measured temperature and was recorded continuously. Feed tanks, tubing, pumps and valves were made of stainless steel and had teflon seals. 

Breath Connect Teflon sampling probe to analyzer and syringe through a sampling valve and loop insert probe 4 cm into mouth between closed lips withdraw 20 mL over 6 seconds into syringe flush and fill the sample loop with 10 mL mouth air carry sample to analysis in nitrogen gas. GC/FID 7ppb NR Blanchette and Cooper 1976... 

Reaction rate experiments were conducted in NMR tubes sealed with Teflon valves. In an inert atmospere glovebox, catalysts and internal standard, TMS4C, were weighed into the tube, followed by addition of solvents and reactants. The tube was immediately inserted in the preheated (50 °C) probe of a 500 MHz Varian Unitylnova spectrometer. To acquire spectra the sample was irradiated twice with a 30° pulse, 5 sec acquisition time, and 120 sec delay. 

The sample loop, Vg, has a volume of 0.25 cc. To initiate injection at time zero of the experiment, the valve handle is rotated 60°, and the flows within the valve are redirected along the dashed lines as shown in the figure. The sample solution in the loop is then displaced through port F by the 1% acidified brine from the pump. The sample loop therefore must be long enough to contain a sufficient "slug" of sample solution. Here, the phrase "sample solution" refers to the surfactant solution prepared in 1% acidified brine solution. Teflon tubing and connections are used to minimize the uptake of any corrosion products into the 1% acidified brine solution. 

Figure 2 Schematic diagram of a 100-mL UV-autoclave. a = gas and sampling valve, b = thermocouple, c = quartz window, d = Teflon O-rings, e = autoclave lid, f = rupture disc, g = valve and pressure gauge, h gaskets, i = autoclave body, k = glass insert, 1 = temperature control, m stirring bar. (Pmax 300 bar, Tmax = 150 °C) (Reproduced with permission from Ref. 7. Copyright 1983 Elsevier Sequoia.)...

There are a number of vendors that sell solenoid actuated Teflon valves, which are easily interfaced to a computer. Care must be taken to chose a design where the internal volume at the valve outlet can be flushed easily between steps, however [110], Rotary selection valves have been used as well, but given the number of rotations needed for a 200 cycle deposit, various failure modes revealed themselves. 

A solution of tri(p-methoxymethyl)phenylphosphine (0.500 g, 1.26 mmol) in dry methanol (5 ml) was placed in a pressure tube with a Teflon needle valve along with p-(methoxymethyl)bromoben-zene (0.255 g, 1.26 mmol) and anhydrous nickel(II) bromide (0.007 g, 0.032 mmol). The tube was flushed with dry nitrogen and closed. The tube was maintained in an oil bath heated at 180°C for 48 h. After cooling to room temperature, the solvent was evaporated under reduced pressure to give the crude product, which was purified by flash chromatography on silica gel (50 g) using 1 1 acetonitrile ethanol as eluent. In this manner was isolated pure tetra(p-methoxymethyl)phenylphosphonium bromide (0.050 g, 7%), which exhibited spectra and analyses in accord with the proposed structure. 

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