Distillation columns Vigreux

Fig. A3.13. Setups for atmospheric pressure distillation (a) for simple distillation (b) Vigreux column for fractional distillation.

A 25-cm spinning band column of 12 theoretical plates, manufactured by NORMAG GmbH, D-6238 Hofheim, FRG, has been used by the submitters. The checkers found a 30-cm Vigreux distillation column just as suitable for the separation. 

A short-path distillation procedure may be used in situations where a simple distillation is required, as purification from non-volatile components/fractional distillation with a Kugelrohr apparatus is difficult. A water-jacketed, semi-micro distillation apparatus is illustrated in Figure 1.7. Heating can either be achieved with the aid of an oil-bath, an isomantle, or a flame (Caution ensure that there are no flammable solvents nearby). For larger scale distillations, a round-bottomed flask should be attached to a distillation column, a still-head, and condenser. The column used in the distillation is variable, and may be either a Vigreux column or a column packed with glass helices. 

A 500-ml flask was equipped with a mechanical stirrer and a Vigreux distillation column, which in turn was connected lo a dry icc trap, and maintained under N The flask was charged with 1-methvlpyrrolidin-2-one (400 mL), l,l,2.2-tetrafluoro-3-(iosyloxy)propane4 (145 g. 0.507 mol), and splay-dried KF (87 g, 1.5 mol). The mixture was then heated lo 190-200 C for about 3.25 It during which time 61 g (90% crude yield) of volatile product distilled into the cold trap. Upon distillation, ihe main fraction boiled at 25-28 C. 

At normal pressure, the ammonia formed on silylation with HMDS evolves so rapidly it does not react with any silylated hydroxy-N-heterocycle to give the corresponding aminoheterocycle. Trimethylsilanol and hexamethyidisiloxane both exhibit a boiling point of 99°C, but form an azeotropic mixture boiling at 70-90°C. Since HMDS has a boiling point of I26°C, it is advisable to remove trimethylsilanol and hexamethyidisiloxane continuously with a small Vigreux distillation column to accelerate the reaction and follow its progress. 

Separation of liquids whose boiling points are between 5°C and 50 C apart requires the use of an apparatus which gives better contact between the vapour and liquid phases in the distillation column. One of the most common types of fractionating column, a Vigreux column, is shown in Fig. 11.9a. A 50cm long vacuum jacketed Vigreux should allow reasonable separation of compounds which bod 30-40°C apart. 

A mixture of DAMN (100 g, 0.925 mol) and trimethyl orthoformate (350 ml, 3.20 mol) is stirred and heated under partial reflux through a 25 cm Vigreux distillation column. Around 200 ml of distillate, mainly methanol and methyl formate, is collected, b.p. 50-70°C, over 140 min. The distillation temperature is allowed to rise to 102°C, and distillate is slowly collected over 2h (the pot temperature is 115°C). The fractionating column is removed, and the bulk of the remaining ortho ester is distilled off. The residue is distilled... 

Isolation of Volatiles. An aliquot of blended pulp (1.2 kg) was diluted with distilled water (700 mL) in a 3-L three-neck flask and vacuum distilled (25-30°C/l mm Hg). Distillation continued for 2.5 to 3 h yielding approximately 500 mL of distillate which was collected in two liquid nitrogen cooled traps. A total of 3.6 kg of fruit pulp was distilled in three batches. The distillates were combined and immediately frozen until use. The combined distillate was extracted in 250 mL batches for 20 h with 60 mL trichloro-fluoromethane (Freon 11, b p 23.8°C) using a continuous liquid-liquid extractor. The trichlorofluoromethane was distilled through a 120 x 1.3 cm glass distillation column, packed with Fenske helices, prior to use. Each extract was carefully concentrated to approximately 100 pL by distillation of solvent using a Vigreux column (16 cm), and a maximum pot temperature of 30°C. 

Figure 3-22. Several distilling columns shown from left to right Hemple. Vigreux. Snyder. Perforated plate. (Courtesy - Ace Glass Co., Vineland, NJ)...

Figure 6-20. Minimum-component vacuum distillation apparatus. (A) pump, (B) and (C) Variacs, (D) support plate, (E) terminal strip, (F) stirring motor, (G) heating mantle, (H) r. b. flask, (I) Vigreux distilling column, (J) distilling head, (K) thermometer, (L) Liebig condenser, (M) manostat, (N) stopcock, (O) stopcock, (P) bleeding valve, (Q) drying tower, (R) U-tube manometer, (S) trap, (T) Dewar flask, (U) support plate, (V) r. b. flasks, (W) cow, (X) vacuum adapter, (Y) stopcock, (Z) Hg overflow, (AA) trap, (BB) Dewar flask, (CC) McLeod gauge, (DD) cork rings.

V) with 45 g NaOH in 170 ml water for two hours or until no more CO2 is evolved. Cool, acidify with 6N HCl and boil 3 minutes. Extract the oil with ether and dry, evaporate in vacuum the ether (can distill on Vigreux column 123/0.01, oil bath 160° C) and let oil stand in refrigerator until crystalline to get about 21 g olivetol. See CA 70,77495t(1969) for another variant of this procedure. 

Miniscale fractional distillation columns (a) Hempel column filled with packing material (b) Vigreux column. 

Liquid-liquid extraction. Tomato Suits were blended and centrifuged in a procedure similar to that used with the SPME technique. Volatiles in the supernatant were extracted with Freon for 20 hours at room temperature, and the extract concentrated to 10 pL in a water bath at 23°C using a Vigreux distillation column. 

Fig. II, 16, 1 illustrates a set-up for simple fractionation a Hempel column is shown, but it may be substituted by a modified Hempel, a Vigreux or an all-glass Dufiton column. The Hempel column may be filled with glass rings, h porcelain Lessing rings, or with porcelain rings. The mixture to be fractionated is placed in a bolt - head flask of convenient size (it should be one third to one half full), a few fragments of porous porcelain added, the column fixed in position, and a water condenserattacfied to the side arm. The distillate is collected in small flasks or in test tubes. The bulb of the thermometer should be just below the level of the side arm.

Alternatively, an independent column (Fig. XII, 2, 8, c) may be inserted into a flask the column may be of the Vigreux, Widmer or Hempel form. The fractionating column should be lagged with asbestos cloth or string for distillation temperatures above 100° for the best results the column should be heated electrically (compare Section 11,15) to a temperature 5-10° below the b.p. of the fraction being collected. The side arm of the flask or fractionating column may be attached to a cold spot condenser and receiver as in Fig. XII, 2, 4 or to a Liebig s condenser and receiver as in Fig. XII, 2, 1. 

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