M. Benton Naff and William Spector
Diclinson College Carlisle, Pennsylvania
I1
Vacuum Distilla+ion with an a11 Glass Rotary Evaporator
In the purification of high boiling compounds by vacuum distillation an all glass rotary evaporator is useful. The apparatus illustrated in the drawing is commercial equipment with slight modification. The set-up consists of a round-bottom flask with a +10/30 thermometer joint sealed to the bottom, a Buchler rotary evaporator and glass sleeve (324/40 teflon coated male joints), a Rinco solvent recovery flask, and a +24/40 female adapter. The Buchler teflon ball and socket vacuum outlet is used to connect the adapter on the condensing flask to a
cold trap of chloroform-carbon tetrachloride-dry ice. The cold trap is connected t o the manometer and vacuum pump via a T-tube. I n aligning the equipment it is essential to angle the set-up so the evaporator flask is slightly higher than the condensing flask. This aids drainage in case the distilled compound solidifies in the connecting tube and must be melted by an infrared lamp. I n some cases it may be necessary to cool the condensing flask with tap water. A pressure of 1mm can be attained with the apparatus described. This equipment is very useful in the purification of glycols, e.g., in the distillation of ethylene glycol or diethylene glycol, following treatment with sodium borohydride and in the purification of 2-butyne-1,4-diol. On standing in a closed container in the dark, butynediol gradually undergoes decomposition. A dark tarry product forms. Therefore, the glycol must be purified just prior to use in synthesis. I n the apparatus described, 100 g of butynediol (General Aniline and Film, distilled grade), mp 48-5G0C and amber-brown in color, was distilled a t 1-2 mm pressure and a temperature of 104-106°C (oil bath temperature 125 + 5'C). The distillation required twenty-five minutes and yielded 94.5 g (94.5%) of white solid, mp 56-58'C.. lit. 58%' REPPE,W.,
Vacvum distillation with o n all-glorr rotory evaporotar.
ET AL.,
Ann. 596, 25-38 (1955); C. A , , 50,
16773l.
Volume 40, Number 6, June 1963
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327
