Opening sealed tubes

Explosions sometimes resulted on opening sealed tubes in which complex mixed chloride salts of this compound had been prepared. There is no obvious source of pressure in the reaction mixture of tungsten hexachloride, sodium and aluminium chlorides and aluminium metal. 

Opening Sealed Tubes.—The greatest possible care must be observed in handling an unopened tube. It must never be removed from its protecting case for examination or for any other purpose. It must not be opened until perfectly cold, and when being opened it is held in such a position that no one can be injured should it burst. 

Full directions are given on p. 44 for opening the capillary. After opening the capillary the tube is removed from the case and examined to see if it still contains crystals or oily drops of the undecomposed substance. If it does, the capillary is again sealed and the tube reheated in the furnace but if it does not, a deep file scratch is made in the wide part of the tube, about 3 cms. below the shoulder of the capillary, and the end broken off according to the second method of opening sealed tubes (P- 44). 

Fig. 4. (a) Standard seal-off tube (fitted with breakseal). (6) Attachment to vacuum line for opening sealed tubes and purifying contents. 

A mixture of 4-bromo-l-(4-methylphenylsulfonyl)indole (88 mg, 0.25 mmol), methyl a-acetamidoacrylate (91 mg, 0.64 mmol), PdCl2(PPh3)2 (16 mg, 0.023 mmol) and NaOAc (82 mg, 0.98 mmol) in EtjN (0.8 ml) and DMF (0.4 ml) was heated to 120°C in a sealed tube for 2 h. The tube was opened and the contents diluted with EtOAc and filtered through Celite. The EtOAc was washed successively with 10% HCl, sat. NaHC03 and brine and then dried (MgS04). The residue was purified by elution through silica gel with 10 1 benzene-EtOAc to give the product as a yellow solid (93 mg, 90%). 

I) Dissolve 2.465 g Na3lrCIg in water and dilute to volume. (2) Transfer 1.000 g Ir sponge to a glass tube, add 20 ml of HCI and 1 ml of HCIO4. Seal the tube and place in an oven at 300°C for 24 hr. Cool, break open the tube, transfer the solution to a volumetric flask, and dilute to volume. Observe all safety precautions in opening the glass tube. 

The following description is taken from U.S. Patent 2,712,012 2.3 parts of clean sodium metal is dissolved in 50 parts of anhydrous methyl alcohol. 11.4 parts of 3-sulfanilamido-6-chloropyridazine is added and the mixture heated in a sealed tube 13 hours at 130° to 140°C. After the tube has cooled it is opened and the reaction mixture filtered, acidified with dilute acetic acid, then evaporated to dryness on the steam bath. The residue is dissolved in 80 parts of 5% sodium hydroxide, chilled and acidified with dilute acetic acid. The crude product is filtered and then recrystallized from water to give 3-sulfanilamido-6-methoxypyridazine of melting point 182° to 183°C. 

Compound 6 is a pivotal intermediate in Schreiber s synthesis. It was hoped that the conspicuous and strained bridgehead cyclobutene substructure in 6 would undergo a conrotatory electrocyclic ring opening upon thermolysis to give an isomeric 1,3-diene (8, Scheme 1). In the event, when a solution of cyclobutene 6 in toluene is confined to a sealed tube and heated to 180°C for 12 h, a stereoisomeric mixture of 1,3-dienes 7 and 8 is produced in an excellent yield of 95% (7 8 ca. 5 1). Finally, irradiation of the 5 1 mixture of cis-7 and trans-8, or of each independently, establishes a photostationary state in which the desired trans isomer 8 predominates (8 7 ca. 10 1). 

Polymerization of Lipid 2 by Free Radical Initiation. Into a polymerization tube was placed 110 mg of Lipid 2, 2 mg of AIBN and 1 mL of benzene. After the tube was evacuated and flushed three times with nitrogen gas and sealed under vacuo, the tube was heated overnight at 60°C. After the sealed tube was opened, the mixture was dissolved in a small amount of chloroform, and this chloroform solution was added to a large excess of methanol. The precipitated polymer was collected by filtration. After the solid was dried in vacuo, 78 mg (71%) of polymer was isolated. 

The scale of the procedure described for preparing [octamethyltetrabenzoporphi-nato (2—)]cobalt(II) by heating the reagents in an evacuated Carius tube at 390°C must not be increased or the tube will explode. Personal protection is also necessary when opening the sealed tube. 

The structures of the radical anions were confirmed by the following experiment (Scheme 9). The reduction of the ladder polysilanes was monitored by UY-visible-NIR spectroscopy. When the absorption of the ladder polysilanes was completely replaced by the absorption of the radical anions, the sealed tube was opened. The radical anions were immediately oxidized, and the starting ladder polysilanes were recovered in high isolated yields. It is reasonable to conclude that the radical anions of the ladder polysilanes retain the ladder structure, and the Si-Si bond cleavage or skeletal rearrangement does not occur. 

Photocycloaddition of allene to cyclohexenone (341) gave the (3,y-enone (342), which reacted with vinyl magnesium bromide to produce the tertiary alcohol (343) in 79% yield. When the compound (343) was treated with KH and 18-crown-6 in THF at room temperature for two hours and quenched with aq. NH4C1, the cyclobutene (344) was obtained. The thermal ring opening of the cyclobutene (344) proceeded in toluene in a sealed-tube at 180 °C for twelve hours to give a readily separable 5 1 mixture of the civ-olefin (345), and the trans-olefin (346) respectively in 95 % yield. Moreover, (345) could be converted to a mixture of (346) and (345) in the ratio of 10 1 by irradiation. The compounds (345) and (346) possess the skeleton of the germacranes (347), (348) and (349) 122). 

Seal, heat, and open the tube as described for the determination of halogen. 

OctafluorotelluranthreneTellurium powder (5.0 g, 39.2 mmol) and 10.0 g (24.9 mmol) of 1,2-diiodotetrafluorobenzene are placed in a 20 cm test tube, and the tube evacuated to 0.2 torr and sealed. The sealed tube is placed in an oven at 300°C for 1 day, cooled and carefully opened. The solid and liquid in the tube are extracted with dichloromethane, the mixture is filtered, and the filtrate is washed first with 50 mL of concentrated aqueous sodium thiosulphate solution and then with 50 mL of distilled water. The solvent is removed under vacuum, the residual dark brown oil is dissolved in chloroform, and bromine is added until the colour of bromine persists. The precipitate is filtered and washed with chloroform to give 5,5,10,10-tetrabromoperfluorotelluranthrene. Yield 3.5 g (29%) m.p. 281°C. 

If any of the reactants are volatile or air sensitive, then this simple method of heating in the open atmosphere is no longer appropriate, and a sealed tube method will be needed. 

We also discovered the ability of 2-azadienes of this sort to cycloadd to unactivated carbon—carbon double and triple bonds in an intramolecular fashion (89CC267) (Scheme 50) such a process appears to be one of the first examples of intramolecular [4 + 2] cycloadditions of simple 2-azadienes. Azadiene 216 was made from O-allyl salicylaldehyde 215 (R = allyl) and heated at 120°C in toluene to furnish the trans-fused tricyclic adduct 217 in excellent yield further dehydrogenation of 217 with DDQ afforded 5H-[ 1 ]-benzopyran[4,3-6]pyridine 218. On the other hand, when 0-(2-butynyl) salicylaldehyde 215 (R = 2-butynyl) was transformed into azadiene 219 and subjected to heating in a sealed tube at 150°C, pyridine 222 was isolated in very high yield. Its formation can be rationalized to occur via the expected Diels-Alder intermediate 220 thus, [1,5]-H shift in 220 would give rise to tautomer 221, which would suffer electro-cyclic ring-opening and aromatization to pyridine derivative 222. 

---