Vacuum traps

Carbethoxy-4-piperidone (7.52 g, 43.9 mmol) (Note 6) and p-toluenesulfonic acid (5.0 g, 26 mmol) are added to a 250-mL, round-bottomed flask that contains the above distillate and a magnetic stir bar. The mixture is stirred under vacuum (20 mm) at 100°C for 90 min and the evolved water vapor is collected in a vacuum trap. The mixture is cooled to 23°C and subjected to flash chromatography on silica gel (250 g, 20 cm x 10 cm) using ethyl acetate hexane (1 4) as the eluant (Note 7) to give 9.0 g (59% overall) of (2R.3S)- and (2S,3S)-1,4-dioxa-2,3-dimethyl-2-(1-methylethenyl)-8-... 

Several volatile components of papaya (Solo variety) were recovered by four methods vacuum trapping train (distillation under low temperatures with liquid nitrogen traps), codistillation-extraction (vacuum), vacuum distillation, and codistillation-extraction (1 atm) [17]. In spite of great variations due to the recovery method, the results showed that linalool was always the major compound detected for all the methods. 

If excessive tailing of the pyridine peak in the chromatographic trace causes difficulty in interpretation (e.g. with pentoses) proceed as follows. Transfer the supernatant liquid of the centrifuged solution by means of a dry dropper pipette to a small test tube and attach a suitable adapter which is fitted to a cooled vacuum trap and pump. Remove the pyridine under reduced pressure continuous agitation of the tube in a water bath held at about 50 °C is advisable. Dilute the viscous residue with 0.5 ml of dichloromethane and re-chromatograph. 

When the evaporation is complete, the 0°C. trap will contain a few milliliters of diglyme the — 196°C. trap will have trapped-out diborane (caution) and the — 126°C. trap will have retained the dimethyltin dihydride together with traces of diglyme and diborane. The crude product is accordingly subjected to a second vacuum fractionation through clean, 0°C. and — 126°C. vacuum traps into the same — 196°C. trap. The diborane collected in the — 196°C. trap is destroyed as described in Sec. A. The colorless, volatile liquid product is identified from its vapor-phase infrared spectrum14 and from its refractive index, nf> 1.4475, literature,2 n 1.4480, as dimethyltin dihydride. The yield is 8.25 g. (0.055 mole, 96%). 

After the heating period is complete, the nitrogen stream is again initiated and the mixture is cooled to 30°. The addition funnel and reflux condenser are replaced with two gas inlet tubes with stopcocks. One inlet tube is connected to the nitrogen source and the other to a standard vacuum trap with at... 

Fangs or stingers are inserted into thick, soft vinyl tubing. The mouth is suctioned with a pipette attached to a vacuum trap. This is more difficult than milking, but yields double the venom. 

The complete manifold (including vacuum trap) is available from Crown Glass Co., 990 Evergreen Drive, Somerville, NJ 08876. Quotes furnished upon request. 

In a 250-mL, three-necked, round-bottomed Pyrex-glass vessel, equipped with a Teflon stirring bar, an addition funnel (125 mL), and a West (Kontes) reflux condenser to which a 100-mL Pyrex glass vacuum trap (cooled to - 80°C) is attached, petroleum ether (75 mL, 90-120°C fraction EM Science) is heated to reflux and KOH (4.8 g, 85.7 mmol Baker) is added. The compound, SF5CFHCF2Br (12.6 g, 43.6 mmol), is added slowly over 1.0 h, and additional KOH (5.2 g, 92.9 mmol) is added during this period (the KOH turns brown and sludge-like). The mixture is allowed to heat at reflux for an additional 0.5 h. The pure product, SFjCF=CF2 (7.5 g, 36.1 mmol) is collected in the — 80°C trap in a 82.8% yield. The IR spectrum agrees with that reported previously. ... 

This product is volatile. The checkers found one-third of the product in a vacuum trap after 24 hr at ca. 5 nrn. 

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