Cold finger apparatus

Trimethylamine oxide (Aldrich) must be freshly sublimed for the procedure that follows. Typically, 2 g of trimethylamine oxide is sublimed in a cold finger apparatus (60 °C, 0.05 torr, 16h). Dry trimethylamine oxide is very hygroscopic. It is important to handle it in a dry atmosphere using suitably dried solvents. 

Molecular distillation (section 5.4.4) on a micro-scale may be performed by both the cold-finger method and that of the falling film or thin layer. A practical example of a cold-finger apparatus is illustrated in Fig. 131 [10]. The mixture to be separated is heated in A, and condenses on the cold finger B the distillate builds up at C, from... 

A further simple, but very efficient and powerful technique to obtain important information especially on the purification by melt crystallization is the so-called cold finger experiment. Compared to the bottle test, more but simple lab equipment is required for this setup. Figure 15.7 shows the essential parts of a cold finger apparatus allowing a static operating mode. 

Figure 15.7 Cold finger apparatus (static) (accordingto Ref. [13] see also Refs [4, 14]).

Compound 1. Boron trichloride was condensed (33 mL) using a cold finger apparatus and added in one portion to a suspension of 12 (15 g, 29 mmol) and 1,2-dichloroethane (170 mL) cooled at 0°C. The resulting purple mixture was... 

Sublimation under reduced pressure. The so-called vacuum sublimation may be carried out in the apparatus of Fig. II, 45, 4. The cold finger is fitted into the larger tube by means of a rubber stopper... 

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. 

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 Dewar seal is important and useful, although a ring seal can sometimes be substituted in simple apparatus—as, for example, in the cold finger liquid air trap shown in Figure 52, III. In the making... 

Fig. 10. Apparatus for the sublimation of decaborane. (A) cold finger (B) ground-glass joint for connection to high-vacuum system (C) high-vacuum stopcock ...

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. 

Figure 88 shows two forms of sublimation apparatus. Note all the similarities. Cold water goes in and down into a cold finger upon which the vapors... 

Dimethyldibenzotellurophene. Powder tellurium (0.94 g 7.4 mmol) is thoroughly mixed with 2.61 g (6.1 mmol) of pure 4,4-dimethyl-2,2 -biphenyldiyl mercury, the mixture is placed into a sublimation apparatus equipped with a cold finger, and slowly heated under vacuum in a metal bath to 260-270°C. Colourless needles begin to sublime at 228°C. The temperature is held at 260°C for 12 h. The sublimate is recrystallized from a mixture of 300 mL of methanol and 10 mL of carbon tetrachloride. Yield 1.38 g (79%) m.p. 158°C. Dibenzotellurophene was similarly obtained in 82% yield. 

TelluranthreneP Finely powdered tellurium (2.3 g, 18 mmol) and 2.5 g (9.0 mmol) of o-phenylenel mercury are intimately mixed by grinding in a mortar, the mixture is placed in the well of a sublimation apparatus, which is then evacuated to <1 torr. The well of the sublimation apparatus is heated at 250°C in a bath of Wood s metal for 10 h, and the cold finger is cooled with dry ice. The sublimed solids are dissolved in chloroform, the solution is decanted through a filter, the solvent is evaporated, and the residue is recrystaUized from carbon tetrachloride or ethanol/benzene. Yield 1.05 g (57%). m.p. 179°C. 

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). 

Some of the more important uses of distillation in high vacuum apparatus which will be encountered later in this hook, are transfer of a liquid by means of a cold finger into a vessel which cannot itself be cooled blocking access to vessels by means of a temporary, or freeze , valve washing reaction products repeatedly and progressively with a single batch of solvent washing the interior of ducts free from solids. 

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 ... 

LiCl-free BuNTe(n-N Bu)2TeN Bu is obtained via vacuum sublimation. In a typical experiment a sublimation apparatus is charged with 1.770 g of the crude product. Sublimation is conducted at 90-95°C/10 mbar with the cold finger at 18°C. Over 24 h pure BuNTe(p-N Bu)2TeN Bu sublimes onto the cold finger as a yellow-orange solid (1.239 g). 

Figure 9. Cold finger sampling apparatus used in matrix isolation-EPR measurements of Mihelcic et al. (97). (Reproduced with permission from reference 97. Copyright 1985 Kluwer Academic.)...

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