Traps dry ice

In the HPLC mode, most solvent vapors and pyrolysis products are similarly trapped in a series of two cold traps (dry ice + ethanol). This has been found to be quite efficient in removing most organic solvent vapors, but is unworkable with aqueous mobile phases because of freeze-up and blockage of the cold traps. Also, traces of moisture entering the detection chamber interfere with the chemiluminescence detection. Furthermore, mobile phases containing in-... 

With the exception that — 80°C. traps (Dry Ice-acetone) are used instead of the — 126°C. traps, this synthesis is accomplished as detailed above in Sec. C. From 14.9 g. (0.075 mole) of trimethyltin chloride and 10.0 g. (0.26 mole) of sodium boro-hydride, an 11.4-g. (0.069-mole, 92%) sample of a colorless liquid product was obtained. The product was identified as trimethyltin hydride from its gas-phase infrared spectrum 14 from its boiling point, 58°C./752 mm., literature,2 59°C./760 mm. and from its refractive index, n 1.4472, literature,2 1.4484. 

The substances which stop in the —196° traps are combined and then warmed slowly to room temperature while distilling through a —78° trap (Dry Ice and acetone) into a —196° trap. This is represented as... 

A 250-mL flask is used as the pot, connected to a 100-mL collection bulb, connected to a cold trap (dry ice-acetone) to protect the vacuum pump. Hexamethyldisilazane is collected first in the cold finger (-78°C). Then, as soon as the diene starts to distill, the collection bulb is cooled with ice. The checkers recorded a bp of 60-80°C at 0.07 mm. 

A set-up for distillation under reduced pressure is shown in Fig. 11,60,3 it is generally more convenient to use a Kon receiver or a Perkin triangle (Fig. 11, 56, 31). The vessel at the side, connected to the assembly by rubber pressure tubing, may be immersed in a Dry Ice-acetone bath and serves as a trap for volatile materials. 

After the addition of the propyne the thermometer-gas outlet combination was replaced with a "cold finger" filled with dry-ice and acetone. The top of this reflux condenser was connected via a plastic tube with a cold trap (-75°C) containing 50 ml of dry THF. The cooling bath was removed and the conversion of propyne started... 

The proper volume of acetylene is measured with a water gasometer as described in Ovg. Synth., Colleat. Vol. 1 1941, 230, with two modifications (a) Two traps immersed in an acetone-dry ice bath at -65°C are placed between the acetylene tank and the gasometer in order to remove acetone. (b) The washing bottles between the gasometer and the reaction flask are replaced by a drying tube (2 x 30-cm column packed with anhydrous CaCl2). 

A. 2-(Trimethtjlsiloxymethyl)allyltvimethylBilane. An oven-dried (Note 1) 2-L, three-necked, round-bottomed flask is equipped with an air-tight mechanical stirrer (Note 2), a 500-mL pressure-equalizing dropping funnel (Note 3), and a reflux condenser. The top of the condenser is connected to a three-way stopcock with one branch connected to a nitrogen source and the other to a variable pressure oil pump with a dry-ice trap (Note 4). The apparatus is flamed dry under a steady stream of nitrogen. The flask is... 

NaBH4 has also been crystd from isopropylamine by dissolving it in the solvent at reflux, cooling, filtering and allowing the solution to stand in a filter flask connected to a Dry-ice/acetone trap. After most of the solvent was passed over into the cold trap, crystals were removed with forceps, washed with dry diethyl ether and dried under vacuum. [Kim and Itoh J Phys Chem 91 126 1987.] Somewhat less pure crystals were obtained more rapidly by using Soxhlet extraction with only a small amount of solvent and extracting for about 8h. The... 

Trimethylsilyl trifluoromethane (trifluoromethyl trimethylsilane) [81290-20-2] M 142.2, b 54-55°, 55-55.5°, d 0.962, n 1.332. Purified by distilling from trap to trap in a vacuum of 20mm using a bath at 45° and Dry ice-Me2CO bath for the trap. The liquid in the trap is then washed with ice cold H2O (3x), the top layer is collected, dried (Na2S04), the liquid was decanted and fractionated through a helices packed column at atmospheric pressure. H, C, F, and Si NMR can be used for assessing the purity of fractions. [Tetrahedron Lett 25 2195 1984 J Org Chem 56 984 1991.]... 

A short-path distillation apparatus is used, the distillate (oxa-spiropentane plus dichloromethane) being trapped in a reeeiver placed in a methanol-dry ice bath cooled to — 80°. The checkers found it useful to drive out last traces of product by adding several milliliters of dichloromethane to the residual thick paste and distilling. The proton magnetic resonance spectrum (dichloromethane) shows an oetet at 8 0.85 and a singlet at S 3.00 in the ratio 4 2. 

If it is inconvenient to add sulfur tetrafluoride directly from a cylinder, it may first be condensed in a calibrated trap containing a boiling chip and cooled in a acetone-dry ice bath. When cooled to — 78°, 119 g. of sulfur tetrafluoride is about 62 ml. The sulfur tetrafluoride can be added to the cooled flask by allowing it to distil slowly from the trap. 

The reaction mixture and contents of the cold trap are then transferred (Note 7) to a 500-ml. distilling flask attached through a short fractionating column to a water-cooled condenser which is connected in series to a receiver, a trap cooled in a dry ice-acetone bath, and a hydrogen chloride absorption trap which may later be attached to a water pump. The mixture is then distilled until the pot temperature reaches 100° and practically all of the acetyl chloride has been driven over. 

Deuterioammonia (about 5 ml) is generated by adding deuterium oxide (14 ml) to a stirred suspension of magnesium nitride (20 g) in mineral oil (30 ml). Tlie deuterioammonia is collected directly in the reaction flask (equipped with a dry ice condenser) at —79° after passing through a trap which is kept at 0°. 

The diazirines are of special interest because of their isomerism with the aliphatic diazo compounds. The diazirines show considerable differences in their properties from the aliphatic diazo compounds, except in their explosive nature. The compounds 3-methyl-3-ethyl-diazirine and 3,3-diethyldiazirine prepared by Paulsen detonated on shock and on heating. Small quantities of 3,3-pentamethylenediazirine (68) can be distilled at normal pressures (bp 109°C). On overheating, explosion followed. 3-n-Propyldiazirine exploded on attempts to distil it a little above room temperature. 3-Methyldiazirine is stable as a gas, but on attempting to condense ca. 100 mg for vapor pressure measurements, it detonated with complete destruction of the apparatus." Diazirine (67) decomposed at once when a sample which had been condensed in dry ice was taken out of the cold trap. Work with the lower molecular weight diazirines in condensed phases should therefore be avoided. 

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