Fraction cutters

The use of a wide-bore condenser and a simple receiver, without a stopcock, is preferable. Usually the product does not solidify at once, but occasionally it crystallizes during distillation. The use of a fraction cutter is not necessary or advisable. 

The combined acetone extracts were extracted six times with one-fourth volume of ethylene dichloride and the ethylene dichloride extract was evaporated under vacuum to leave the steroid residue. This steroid residue was taken up in a minimum of methylene chloride and applied to the top of a column packed with 30 grams of silica which had been previously triturated with 21 ml of ethylene glycol. Then various developing mixtures, saturated with ethylene glycol, were passed over the column. Cuts were made as each steroid was eluted as determined by the lowering of the absorption of light at 240 mp on the automatic chromatographic fraction cutter. 

If a fraction cutter is not used, the residue should be cooled to room temperature each time before the vacuum is broken. 

The solution is then transferred to a continuous extractor and extracted with ether for about 16 hours. The ether extract is added in convenient portions to a 250-ml. modified Claisen flask fitted with a condenser and a suitable fraction-cutter for distilla-1 ion under reduced pressure. The ether is removed by distillation under the diminished pressure of a water pump, and the residue is then distilled at about 10 mm. pressure. After a small fore-run which weighs 2-5 g., the product distils as a clear, colorless, viscous oil at 62-66°/9-10 mm. n 1.4513. The yield is 00-95 g. (74-79%) (Notes 3 and 4). 

A convenient apparatus for the distillation is a modified Claisen flask whose side arm is provided with a short water-cooled condenser. A fraction-cutter of the pig type is satisfactory. 

A vacuum-jacketed column 1 ft. long by 1 in. I.D. packed with glass hehces (4 mm. O.D.) is satisfactory for this distillation. It is fitted with a cold finger in the top of the column cooled by means of acetone that has been cooled in a Dry Ice bath. The fraction cutter is jacketed and similarly cooled. A small circulating pump is used to circulate acetone successively through copper coils in a Dry Ice bath, the fraction cutter, and the cold finger. When the fraction cutter is full, the bottom may be attached to a cooled, evacuated gas cylinder and the allene sucked into the cylinder. 

Fraction cutters are arranged so that the receiving flask may be... 

When one wishes to change fractions using the fraction cutter described above, the stopcock B on the cutter is turned so that the manostat is still connected to the system but is not connected to the receiver. Stopcock A is turned 180° to connect the auxiliary position of the fraction cutter with that of the pump. Stopcock Sj on the pump table is turned to connect arms x and y and disconnect 2. Air is bled into the system through S3, and the flask is changed. The new... 

Figure 6-16. Distillation head, fraction cutter. (Courtesy - Ace Glass Co., Vineland, NJ)...

Fraction Collection A component of a fractional distillation assembly critical for the satisfactory operation of the fractionation column is the fraction cutter. Its purpose is to allow collection of the distillate and to control the reflux ratio. A fraction cutter should be designed so that no major disturbance of column equilibrium occurs when a change of receivers is made. A widely used manually operated fraction cutter is shown in Fig. 2-16 this is a typical setup for fractional distillation. Two alternative fraction cutters are shown in Figs. 2-17 and 2-18. 

For high precision distillations, it is advantageous to have an automatically controlled fraction collecter. Although these are more expensive, they allow precise control of the reflux ratio and require less attention than their manually operated counterparts. They usually consist of a timing device and a solenoid-controlled valve that is opened automatically on occasion to collect some distillate. The reflux ratio is controlled by the ratio of time the valve spends in the closed and opened positions. In view of the time saved and the greater control available from the use of an automatically controlled fraction cutter, their purchase ( 100) is highly recommended. 

Elmer infrared spectrophotometers. Spectrophotometric readings and spectra on the U.V.-Visible range were taken on a U.V.-Vis Hitachi-Perkin Elmer type 139/ spectrophotometer. Centrifugations were performed on a Sor-vall-superspeed RC-2B refrigerated centrifuge. Water evaporations were done on a Btlchi flash evaporator. Fractions after chromatography columns were collected with a Shandon-MBI fractions cutter. 

Preparative column A 14 Solvent counter and fraction cutter... 

After eluting through the columns, part of the sample flow was dir ted through the differential refractometer detector, the response being plotted on a Chessell chart recorder. The sample flows were then recombin and the automatic fraction cutter(14) was then used to split the column ou ut volumetrically in to fractions of up to 50 cm (each fraction corresponding to one count) and the fraction cuts were automatically deposited into individual collection containers for subsequent work-up. 

Fraktion Teil, Anteil Bruchteil fraction collector F raktionssammler fraction cutter Wechselvorlage fractional crystallization fiaktionierte Kristallisation fractional precipitation fiaktionierte Fallung fractionate fraktionieren fractionating column Fraktioniersaule fractionation Fraktioniemng... 

Fig. 6. A direct recording of the separation of the active adrenal steroids taken from the automatic chromatographic fraction cutter. The per cent of ultraviolet absorption...

The prepared column was loaded with the steroid fraction and developed with mixtures of cyclohexane and methylene chloride, which were saturated with glycol. The sequence of developer mixtures was regulated by the automatic fraction cutter to produce the results shown in Table V. The steroid distribution was corroborated by spot paper chromatograms. Negligible failing could be observed in this separation. 

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