Apparatus cold-finger condenser

Fig. XII, 2, 1). For very small volumes of liquid either of the apparatus depicted in Fig. XII, 2, 10, incorporating a cold finger condenser may be employed subsequent distillation (or steam distillation) is a facile...

Sublimation.—This is a valuable means for the purification of many organic substances and is admirably adapted for small scale work since losses are generally small. Sublimation may be carried out either at atmospheric pressure or under reduced pressure. The apparatus shown in Fig. XII, 2, 20 is simple and effective the sublimate is collected on the cold finger condenser. 

If dry liquid ammonia is needed this is usually obtained by distillation ff sodium. The appropriate volume of ammonia is condensed as above 2nd small pieces of sodium are added to produce a blue solution. The ammonia can then be distilled using a normal distillation apparatus (Chapter 11) except that the receiver (usually the reaction flask) is cooled in a solid bon dioxide/acetone cooling bath. The ammonia in the distillation flask must remain blue throughout). The distillation apparatus is disconnected Srom the receiver which is then fitted with a cold-finger condenser and the reaction carried out as normal. The work up is usually simple. Solid ammonium chloride is added carefully and the ammonia allowed to evaporate (Chapter 10). The product may then be isolated and purified in the usual way. 

Figure 115 shows three forms of sublimation apparatus. Note all the similarities. Cold water goes in and down into a cold finger on which the vapors from the crystals condense. The differences are that one is larger and has a ground glass joint. The sidearm test tube with cold-finger condenser is much smaller. To use them,... 

The checker finds that upon distillation the product crystallizes directly on the cold finger condenser (sublimation apparatus) and can be removed by scraping under anhydrous conditions. 

Sublimations can be carried out under pressure or vacuum with equal ease. The technique is useful only if impurities associated with the component being sublimed have a substantially different vapor pressure at the sublimation temperature. It is often used as a final purification step in the preparation of an analytical sample. A simple but effective apparatus is shown in Fig. 2-6 the sample is placed in the bottom of the outside tube, it is heated, and crystals of sublimate collect on the large cold-finger condenser. A simple tube such as that illustrated in Fig. 2-7 can be used for... 

The most successful method for purifying volatile acids, ammonia solutions, and solvents, and which is operated on a small commercial scale, is that of subboiling distillation. The apparatus is constructed from quartz or, for hydrofluoric acid, of polytetra-fluoroethylene (PTFE), and infrared radiators vaporize the surface of the liquid without bringing it to the boil. The vapor is condensed on a tapered cold-finger condenser and the liquid is collected in a suitable container, itself constructed from quartz or PTFE. Apparatus is available that will deliver 20 or more liters per still per day. 

Apparatus 3-1 round-bottomed, three-necked flask, provided with a dropping funnel, a mechanical stirrer and a reflux condenser, cooled with dry-ice and acetone (cold finger). The upper end of this condenser was connected with a drying tube filled with anhydrous calcium chloride. 

The apparatus shown in Fig. 16 is set up in the fume hood. The equipment is flushed with dry nitrogen, then a 200-ml. portion (314.8 g., 2.29 mols) of phosphorus trichloride is placed in the 2-1. reaction flask. The flask is partially immersed in the Dry Ice-isopropyl alcohol bath the clamp to the alkylamine container is opened and a stream of dry nitrogen is passed through the system at a rate of about 30 cc./minute measured at S.T.P. The nitrogen stream sweeps the anhydrous amine (200 g.) from the bottle into the reactor. The amine usually condenses on one of the two cold fingers of the reactor and drips into the chilled stirred phosphorus trichloride solution. Finely divided dimethylammonium chloride precipitates immediately. 

A short path distillation apparatus with a cold finger but no condenser should be used since the product may crystallize. The distillation is carried out under nitrogen or argon (balloon at capillary). 

Apparatus for CHjOeCH, C HjCsCH and H2C=CHCsCH a 1-1 three-necked, round-bottomed flask, equipped with a gas inlet tube, a mechanical stirrer and a "cold finger" reflux condenser (-75 C, fig. 17), cooled with dry ice and acetone the top of the condenser is connected to a cold trap ... 

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