Hempel column

A modified Hempel column, which incorporates a small reflux condenser ( cold finger or cold spot condenser ), is shown in Fig. 11,... 

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, a modified Hempel column (Fig. 77,15, 5) or an all glass Dufton column with 30 cm. spiral (Fig. 77,15, 2) may be used for the fractionation. The latter has the advantage that it is more easily cleaned. 

Fit up the apparatus shown in Fig. Ill, 61, 1. The bolt-head flask is of 500 ml. capacity and the Hempel column is fllled with glass rings... 

The best results are obtained b distillation from a small flask through a short fractionating column a Hempel column tilled with glass rings (Fig. 11,16, 1) and lagged with asbestos cloth or several thicknesses of linen cloth is quite satisfactory. 

The 42 per cent hydrazine hydrate solution supplied by the Eastman Kodak Company is too dilute for use as such, but may be concentrated by distillation with xylene.1 A mixture of r44 cc. (150 g.) of the 42 per cent solution and 230 cc. of xylene is distilled from a 500-cc. flask through a 17-cm. Hempel column fitted into a cork covered with tin foil. After distillation of the xylene, with about 85 cc. of water, the residue yields on distillation 45-50 g. of 80-85 per cent hydrazine hydrate. This material, assayed best by titration with standard acid using methyl orange as indicator, may be used as such or concentrated further (see Note 6). 

The pentane extract is dried over 10 g. of anhydrous potassium carbonate. After removal of the drying agent by filtration, the j)entane is slowly removed from the product by distillation through a 20-cm. Hempel column packed with glass helices (Note 6). When the pentane is removed, a white crystalline residue remains which weighs 78-83 g. (88-94% yield based on the hydrogenated Diels-Alder adduct). This 2,3-diazabicyclo 2.2.1 hept-2-ene melts at 98.0-99.5° (Note 7). 

Hempel column. A plain tube (fitted near the top with a side arm) which is almost filled with a suitable packing, which may be of rings or helices. 

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