Improved Apparatus for Continuous Column Chromatography An apparatus was described recently in Organic Syntheses1 for purification of an organic compound by continuous extraction of i t from an adsorbent column. The general technique involves boiling a solvent, such as pentane, leading the vapors to a reflux condenser above the column, and allowing the condensate to fall on the crude, solid compound. The extract is allowed to pass through the adsorbent, usually alumina or Silica Gel, and run into the boiling flask, from which solvent is recycled. Purified compound collects in the boiling flask. A great saving is achieved in the amount of solvent used compared to operation of the column cold, with addition of successive batches of solvent. Purification of very poorly soluble materials is possible. Impurities intractable t o recrystallization can be removed. The technique is to he a, inner column; b. outer recommended to students as a standard procedure. When the solvent is more polar or has a higher boiling point than pentane andlor the jack": c. 401s0 joint: d. 55150 joint; compound is poorly soluble, the apparatus' suffers from several defects. The flexible tube used for vapor tranport is attacked by solvent. Solvent often condenses in the tube and Of 17'20 mm diameter; I. glass frit of "slugs" with danger of fire should it be expelled suddenly. Since the column usually operates just above ambient temperature, the process is often too slow to he worthwhile. An all-glass 30 mrn diameter; joint; h, working form of the apparatus2 solves the problems of tubing and stopper extraction, but the vapor 35125 passage is still constricted, and the column operation occurs a t a temperature gradient con- length Of 40 cm; i, between ductive to deposition of crystals in the interstices of the adsorbent column, often leading to mum very slow operation. The apparatus of Meier and Fletschinger" solves this particular problem column and jacket Of lo i. hy having the entire adsorbent column surrounded by solvent vapor, and the extraction takes to place a t an elevated and even temperature. Their set-up suffers from lack of condensing ca- '"g 'la*; k, condenserpacity, potential extraction of an organic stopper, and a seemingly trivial yet obtuse problem of deposition of dust from adsorbent or eompound between the column and its jacket, which must he assembled before the column is packed. The weight of the filled column rests on glass fingers in the jacket above the hailing flask, with the danger that the fingers may break because they are subject to concentrated loads. An apparatus for returning sublimate t o a reaction vessel developed by Hsieh e t al.' suggested means to overcome all of the ab&e problems. We found (see figure) that the eolumn (4 could be hung from a vapor-retaining jacket (b) by means of a standard taoer ioint (d). Use of a Teflon sleeve in the ioint orevents seizing. Solvent vaoors from the boiling flask m s s between thk jacket and the column, thru holes (ej and bp t o i b e reflux condenser fitted the upper joint (c)YThe cdndenser may he a high capacity type resistant to flooding. Condensate is allowed t o fall on a piece of filter paper or glass wool atop the crude compound, itself upon an adsorbent, all retained in the column by a fritted glass disc (fi which is sealed into 'he lower end of the column. The entire operation takes place a t the boiling point of the solvent. (We have successfully used o-dichlorobenzene, h.p. 17g0.) The column may be packed while clear of the jacket, and the outside cleaned before assembly. The two-piece apparatus is easily taken apart for cleaning, when all surfaces are accessible. Dimensions given in the figure are for an apparatus size suitable for the purification of 1-50 g of compound. The ball joint fg) was preferred to a standard taper because of its larger bore. In building such an apparatus, the area for the vapor passage thru this bore should be maintained with appropriate clearance (r) between jacket and column, and large enough holes, so that no pressure drop occurs even if there are changes in the heating rate, and thus the operating temperature will not vary.
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New England Nuclear Corporation 549 Albany Street Boston. Massachusetts 02118
Joel M. Kauffman Charles 0.Bjorkman
Volume 53, Number 1. January 1976 1 33
