Fractionating columns Vigreux

Any fractionating column of moderate efficiency is satisfactory, e.g., a Dufton column (20 cm. long containing a spiral 10 cm. in length, 2 cm. in diameter with 8 turns of the helix) or a Vigreux column (20-25 cm. long). 

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. 

The dried benzene extract is placed in a 250-cc. flask fitted with a 30-cm. fractionating column, and the benzene is removed by distillation at atmospheric pressure. Fractionation of the residue is carried out under reduced pressure using a 50-cc. Claisen flask with a built-in 12- to 15-cm. Vigreux column. The fraction boiling at 100-103°/13 mm. is collected it weighs 11 to 14.7 g. (41-55 per cent of the theoretical amount) (Note 2). 

A solution of (+ )-car-2-ene (4.08 g, 30 mmol) in petroleum ether (bp 40-60 X, 500 mL) containing toluene (3.1 mL) was irradiated with a 450-W Hanovia medium-pressure Hg lamp using a Vycor filter. The reaction was monitored by GC and the irradiation continued until 93 % conversion (50 h) had occurred. The solvent was slowly distilled off using a Vigreux fractionating column and the residue was distilled at 130-140 C. The product was purified by preparative GC yield 3.04 g (60%). 

The sinter filter is removed and dppe (7.32 g, 18.4 mmol), toluene (70 mL), and a magnetic stirrer are added to the filtrate. A Perkin triangle with a 12-cm Vigreux column is attached (Fig. 1). The Perkin triangle is a piece of apparatus which is used to remove volatile fractions from a boiling mixture. It includes a fractionating column to separate the most volatile fraction,... 

For the reduction of volatile aliphatic aldehydes (b.p. below 150°) Procedure I, employing a Vigreux or a more efficient fractionating column, is recommended. For higher-boiling aliphatic aldehydes Procedure IV may be followed. With aromatic aldehydes, which readily undergo the Tishchenko reaction, an excess of aluminum isopropoxide is to be avoided and Procedure II should be used. 

The apparatus originally attached to the three necks of the reactor is quickly replaced by stoppers (rubber or ground glass) and a Vigreux fractionating column adapted for vacuum distillation. The pressure within the system is slowly reduced to about 25 mm. After the dissolved hydrogen chloride and the unreacted ethanol have been removed, the contents of the still pot are heated slowly. A fraction obtained over the range from room temperature up... 

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. 

Set up the distillation apparatus as described in Box 15.1, but use a two-necked distilling flask and include a short fractionating column between the top of the distilling flask and the still-head or use a Vigreux flask (Fig. 15.2 ) or use a Claisen still-head (Fig. 15.2). 

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... 

Many types of fractionating columns have been designed. However, most of these have proved relatively inefficient, and the principal types presently in use are the Vigreux, bubble-cap, packed, spinning-band, and concentric-tube. Each of these will be considered in turn. 

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