Cold fingers

Miblimation The volatilization of a solid substance into the vapour phase without passing through the liquid phase. Also used to describe the process of purification in which the vapour is condensed directly from the vapour phase to a solid (on a cold-finger often cooled by refrigerant). In the latter case this substance may melt during the initial vaporization. Used for purification. 

Sublimation. This is a most useful process for small-scale work as the losses are comparatively small. This can be performed (a) In a long narrow tube sealed at one end. The material is shaken to the closed end of the tube, which is then inserted horizontally in a metal-heating block (Fig. 50) (b) In the cold-finger device (Fig. 35, p. 62)-... 

Vapours which can be readily condensed e.g., chloroform, aniline, nitro-benzene, etc.) are readily detected by the device shown in Fig. 5 i(b). It is essentially a cold finger with a deep indentation or weU at the lower end. In this way two or three drops of liquid can easily be collected and removed by a capillary tube for qualitative tests. 

Acetylation. Place 1 ml. of the substance (or, if solid, i g. of the powdered amine) in a small flask fitted with a reflux condenser (or in a test-tube fitted with a cold-finger, as in Fig. 35, p. 62), add 5 ml. of an acetic anhydride-acetic acid mixture (equal volumes) and reflux... 

A modified Hempel column, which incorporates a small reflux condenser ( cold finger or cold spot condenser ), is shown in Fig. 11,... 

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... 

Improved results are also secured by the use of a short reflux condenser ( cold finger ), Fig. 11, 56, 22, inserted into the top of the column head the simplest type is shown in Fig. 11, 56, 23. The condenser permits con trol of the reflux ratio by adjusting the rate of flow of water through it. 

Fractional distillation. Fig. II, 60, 2 illustrates a set-up for fractional distillation wdth a Hempel-type column and cold finger, the latter to give manual control of the reflux ratio. Any other fractionating colunm, e.g., an all-glass Dufton or a Widmer column may, of course, be used. 

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. 

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... 

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. 

Friedrichs condenser. A "cold-finger" type of condenser sealed into a glass Jacket open at the bottom and near the top. The cold finger is formed into glass screw threads. 

Azelaic acid [123-99-9] M 188.2, m 105-106". Crystd from H2O (charcoal) or thiophene-free benzene. The material cryst from H2O was dried by azeotropic distn in toluene, the residual toluene soln was cooled and filtered, the ppte being dried in a vacuum oven. Also purified by zone refining or by sublimation onto a cold finger at 10" torr. 

Nitrosobenzene [586-96-9] M 107.1, m 67.5-68 , b 57-59 /18mm. Steam distd, then cryst from a small volume of EtOH with cooling below 0°, dried over CaCl2 in a dessicator at atm pressure, and stored under N2 at 0°. Alternatively it can be distd onto a cold finger cooled with brine at —10 in a vac at 17mm (water pump), while heating in a water bath at 65-70° [Robertson and Vaughan J Chem Educ 27 605 1950]. 

Sodium bis(trimethylsilyl)amide (hexamethyl disilazane sodium salt) [1070-89-9] M 183.4, m 165-167 (sintering at 140 ). It can be sublimed at 170 /2 Torr (bath temp 220-250°) onto a cold finger, and can be recrystd from CgHg (sol lOg in lOOmL at 60°). It is slightly soluble in Et20 and is decomposed by H2O. [Chem Ber 94 1540 1961.]... 

Fig. 4.10. The two main types of dear-ice machine. In the top one, the ice grows on the outside of a set of aluminium cold fingers. In the bottom one, the cubes grow in aluminium troys. Cubes ore removed when they ore big enough by stopping the flow of refrigerant and heating the aluminium electrically. This melts the surface of the ice so that it con fall away from the metal (remember that the easiest way to take the wrapper off on ice lolly is to worm the outside with your hands for a minutel)...

A cold finger condenser packeFriedrichs condenser in combination with a circulating low-temperature bath (— 70°) is more convenient. 

The checkers used a Dry Ice-acetone-cooled cold-finger condenser fitted with a partial take-off adapter. 

AuFj is an unstable, polymeric, diamagnetic, dark-red powder, produced by heating [02][Aup6] under reduced pressure and condensing the product on to a cold finger ... 

Another piece of glassware used in synthetic procedures is the cold finger condenser (Fig. A3.7). Used in the case where the reaction is carried out in a low-boiling solvent (for example, liquid ammonia), the condenser is filled with a suitable cooling mixture and fitted with a drying tube. 

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