Pyrolysis tubes

The pyrolysis tube is flushed with nitrogen, the lower section is heated to 600° and the upper section to 300° (Note 1), and the pressure is regulated at 25 mm. Then 184 g. (1.00 mole) (Note 2) of dimethyl 3-methylenecyclobutane-l,2-dicarboxylate2 is admitted over a period of 3 hours (Note 3). The product, which amounts to 172-177 g., collects in the traps. It is distilled through a 13-mm. x 1.2-m. Nester spinning-band still.3 First... 

Methyl radicals were produced by pyrolysis of azomethane (CH3N2CH3). Azomethane was synthesized as describe earlier [18]. It was purified periodically by fteeze-pump cycles at 77 K, and the gas purity verified by RGA. The methyl radical source was similar to that developed by Stair and coworkers. [10, 11] The source was made of a quartz tube with 3 mm OD and 1 mm ID, resistive heating was supplied by means of a 0.25 mm diameter tantalum wire wrapped outside the quartz tube. The len of the heating zone was 4 cm, recessed from the end of the tube by 1 cm. An alumina tube around the outside of the heating zone served as a radiation shield. Azomethane was admitted to the hot tube at a pressure of 1x10-8 to 1x10-7 Torr via a high-vacuum precision leak valve. The pyrolysis tube was maintained at about 1200 K, adequate to decrease the major peaks in the mass sp trum of the parent azomethane at 58 and 43 amu by at least a factor of 100. 

Controlled furnace-type pyrolyser a, heater b, A1 block c, variable transformer d, gas outlet to column e, Swagelok union f, column oven g, gas inlet h, cement i, glass wool plug j, insulating block k, pyrometer 1, stainless steel chamber m, sample n, heater thermocouple o, pyrolysis tube p, ceramic tube q, line voltage. 

Abbott et al. [163] described a pyrolysis unit for the determination of Picloram and other herbicides in soil. The determination is effected by electron capture-gas chromatography following thermal decarboxylation of the herbicide. Hall et al. [164] reported further on this method. The decarboxylation products are analysed on a column (5mm i.d.) the first 15cm of which is packed with Vycor chips (2-4mm), the next 1.05m with 3% of SE-30 on Chromosorb W (60-80 mesh) and then 0.6m with 10% of DC-200 on Gas Chrom Q (60-80 mesh). The pyrolysis tube, which is packed with Vycor chips, is maintained at 385°C. The column is operated at 165°C with nitrogen as carrier gas (110ml min-1). The method when applied to ethyl ether extracts of soil gives recoveries of 90 5%. Dennis et al. [165] have reported on the accumulation and persistence of Picloram in bottom deposits. 

The carbonaceous material that is deposited inside the pyrolysis tube is easily removed by passing a stream of oxygen through at about 550° after a thorough flushing with nitrogen. 

Oxygen analysis in the presence of fluorine is rarely performed as it is very difficult to achieve using modern elemental analyzers because of the release of hydroxy groups from fixed sites within the pyrolysis tubes.10... 

Apparatus. Pyrolysis experiments were conducted in a quartz tube heated by an induction furnace. A continuous flow of argon was used to sweep out gaseous pyrolysis products. The materials to be pyrolyzed were contained in alundum boats, which could be readily admitted and removed from the quartz pyrolysis tube. 

Caution. Pyrolysis tubes may develop enough pressure to explode and cause serious injury. Only high-quality, thick-walled glass should be used. Protective eyewear and a laboratory safety shield should be used at all times. 

The observed product distributions reflect the influence of both factors. In the parent compound 102 and in the silyl substituted 104, the initially formed open-chain silylenes 103 and 146 are relatively sensitive and the migration tendency of the group R is quite large, and therefore the silacyclopropenylidenes 104 and 145 are found. In contrast, the methyl and the ethynyl compound 138 and 150 are stable enough to pass the pyrolysis tube and both can be matrix-isolated upon pyrolysis of the appropriate precursors 137 and 149. Due to the small migration tendencies of the methyl and the ethynyl group, the rearrangement product 135 is not found at all and 151 is detected only in relatively minor amounts. 

Heterocyclic phosphorus ylides (e.g., 114, R = Me) containing an azepinedione nucleus have been prepared, although in low yield (13-26%), by flash vacuum pyrolysis (FVP) of the corresponding open-chain ylide precursor 113 (Equation 15) <2001TL141>. The authors noted, however, that the azepinediones were isolated from the inlet residue rather than from the cold trap after the pyrolysis tube. 

A 0.331-g sample of hydrated ammonium carbonate was placed in an evacuated 30.0 cm3 pyrolysis tube rated at 45.0 atm. It was heated at 250°C until complete decomposition by... 

The l,4-cyclohexane-bis(methylamine) feed line was connected to the top of the preheater in a pyrolysis tube. The pyrolysis section was heated by external electric heaters. For a typical run, the pyrolysis temperature was... 

Accordingly, a 0-1 molar solution of phthalic anhydride in benzene (100 ml.) was pyrolyzed at 690° under nitrogen at a steady rate of 30 ml/hr (Fields and Meyerson, 1965). The pyrolysis tube was Vycor, filled with Vycor beads contact time was 11 5 sec, which gave a 58% conversion of the phthalic anhydride. Acetylene was steadily evolved, along with carbon dioxide and carbon monoxide in a 1 1 ratio these were identified in the gas stream by mass-spectral analysis of samples taken at regular intervals. The benzene was distilled off and the products boiling over 180° (2 g) were analyzed by mass spectrometry on a Consolidated Model... 

Tetrachlorophthalic anhydride gave a relatively low yield of products derived from tetrachlorobenzyne. The pyrolysis tube was badly carbonized evidently extensive decomposition of the anhydride, the aryne, or the chlorinated products had occurred. Tetrabromophthalic anhydride gave a still lower yield of products. These are not listed in the table because none of them retained all four bromine atoms and could be definitely ascribed to reactions of tetrabromobenzyne, although tri-bromo- and dibromonaphthalene were present in appreciable amounts. Tetraphenylphthalic anhydride also gave low yields of products of the reaction of tetraphenylbenzyne with pyridine. This was not because of the stability of the anhydride and its reluctance to form the aryne, but rather because the aryne preferred to stabilize itself intramolecularly. The behavior of tetraphenylphthalic anhydride is discussed in another Section. 

Visually, there appeared to be very little reaction at 500°C. No solids were deposited on the pyrolysis tube and virtually no gases were formed. Chemically, the most notable change was a... 

A pressure rise of 5-100 p. is generally observed during a pyrolytic polymerization. At the end of the run the pressure falls back to the base pressure. The heating jacket on the distillation section of the pyrolysis tube is removed at this point to ensure that complete distillation of the charge has occurred. When it is established that the distillation is complete, the vacuum is broken, the equipment is dismantled, and the polymeric film is recovered from the walls of the deposition chamber. 

Particle Encapsulation. A unique capability of the p-xylylene vapor deposition process has been uncovered in the area of encapsulation (12) of particulate solids. The particles or granules to be encapsulated are placed in a container which in turn is placed in the deposition chamber, and the nozzle from the pyrolysis tube is inserted in the mouth of the bottle. During the run the monomers pass from the pyrolysis zone through a nozzle into the bottle and polymerize on the surface of the tumbling particles or granules. Polymer is also formed on the inner surface of the bottle which is rotated at 50-150 r.p.m. Relatively simple equipment (Figure 4) has been used to study this phenomenon. 

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