Liquid-nitrogen bath

Fig. XVII-5. Schematic detector response in a determination of nitrogen adsorption and desorption. A flow of He and N2 is passed through the sample until the detector reading is constant the sample is then cooled in a liquid nitrogen bath. For desorption, the bath is removed. (From Ref. 28. Reprinted with permission from John Wiley Sons, copyright 1995.)...

A mixture of 0.40 mol of propargyl chloride and 150ml of dry diethyl ether was cooled at -90°C (liquid nitrogen bath) and a solution of 0.40 mol of ethyl-lithium (note 1) in about 350 ml of diethyl ether (see Exp. 1) was added with vigorous stirring and occasional cooling (note 2). The temperature of the reaction mixture was kept between -70 and -90°C. The formation of the lithium derivative proceeded almost instantaneously, so that the solution obtained could be used directly after the addition of the ethyl 1ithium, which was carried out in 15-20 min. This lithium acetylide solution is very unstable and must be kept below -60°C. 

To a solution of 0,35 mol of allenyll ithium in about 240 ml of hexane and 200 ml of THF, prepared according to Chapter II, Exp. 13, were added 35 g of dry HMPT at -85°C. r.-Hexyl bromide (0.30 mol) was then added dropwise in 15 min, whilst keeping the temperature of the reaction mixture close to -70 0 (liquid nitrogen bath). After the addition the mixture was held at -60°C for an additional 1 h. 

In the flask was placed a solution of 50 g of carbon dioxide in 250 ml of dry THF, made by introducing the gas from a cylinder into THF, cooled at about -90°C (liquid nitrogen bath). The gas inlet was removed and through the neck of the reaction flask was poured a cold solution (-70°C) of 0.40 mol of allenyl1ithiurn in 280 ml of hexane and 280 ml of THF (prepared as described in Chapter II,... 

A solution of 0.20 mol of butyl lithium in about 140 ml of hexane was cooled to -6Q°C and 140 ml of dry THF were added. The mixture was cooled to about -80 C (liquid nitrogen bath) and 0.23 mol of the allenic hydrocarbon (see Chapter VI, Exp. 1, 2, 44) was added in 5 min (methylal1ene was added as a 1 1 solution in THF). The solutions were kept for 1 h at -55°C. Into another 1-1 flask (see also Fig. 1, but without a dropping funnel), cooled at -90°C by immersion in liquid nitrogen, was poured a solution of dry carbon dioxide (from a cylinder) in 130 ml of dry THF. This solution was obtained by introducing about 40 g of carbon dioxide (note 1) into the THF at -90°C. The gas inlet was removed from the second flask and the solution of the lithiated allene (still cooled below -60 C) was poured... 

To a solution of 0.20 mol of LiCEC-CH2Cl in about 300 ml of diethyl ether (see Chapter II, Exp. 16) was added in 15 min with vigorous stirring and cooling between -75 and -90°C (liquid nitrogen bath, note 1) a mixture of 0.20 mol of... 

After the air in the flask had been completely replaced with nitrogen, it was cooled in a liquid nitrogen bath and a solution of 25 g of acetylene in 160 ml of dry THF was introduced. The solution had been prepared by dissolving acetylene (freed from acetone by means of a cold trap) in THF cooled at -80 to -90°C. A solution of 0.21 mol of butyl lithium in about 150 ml of hexane was added in 5 min to the vigorously stirred solution. During this addition the temperature of the mixture was kept between -80 and -100°C by occasionally dipping the flask into the liquid nitrogen. To the white suspension were successively added at -80°C a solution of 10 g. of anhydrous lithium bromide (note 1) in 30 ml of THF and 0.20 mol of freshly distilled benzaldehyde. The reaction mixture was kept for 3 h at -69°C, after which the temperature was allowed to rise to +10°C over a period of 2 h. 

Allene (prodiene) [463-49-0] M 40.1, m -146 , b -32 . Frozen in liquid nitrogen, evacuated, then thawed out. This cycle was repeated several times, then the allene was frozen in a methyl cyclohexane-liquid nitrogen bath and pumped for some time. Also purified by HPLC. [Cripps and Kiefer Org Synth 42 12 1962.]... 

Upon appropriate priming, the activated charcoal reactor A must be evacuated and is subsequently chilled in a liquid nitrogen bath. After an induction period, which depends on the operating pressure, 51% enriched parahydrogen is avail-... 

Upon termination of the experiment, all parts of the apparatus should be evacuated once again, before the liquid nitrogen bath is removed. The same precaution should also be maintained during removal of the bath, in order to safeguard against pressure surges caused by thermal expansion of the residual hydrogen or due to sudden desorption from the charcoal. 

The volatile materials are transferred under essentially static conditions. Bulb-to-bulb vacuum transfer may be accomplished with a standard 24/40 short path distillation apparatus. The reaction flask may be warmed slightly (40°C) with a water bath and the receiving flask is cooled in a liquid nitrogen bath. Vacuum is applied... 

Figure 4 The levitation of a magnet placed above a small platelet of YBa2Cu307-x immersed in a liquid nitrogen bath...

While in the liquid nitrogen bath, the sample (held by the magnetic wand) is manoeuvred into a cryovial, which is held submerged in the liquid with a vial clamp. 

Depolymerizations of polymer and oligomer were performed by heating them at 300 u 350°C under vacuum. The products were collected in the reservoir cooled in liquid nitrogen bath and analyzed by gas-liquid chromatography. 

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