Widmer

Fractional distillation. Fig. II, 60, 2 illustrates a set-up for fractional distillation wdth a Hempel-type column and cold finger, the latter to give manual control of the reflux ratio. Any other fractionating colunm, e.g., an all-glass Dufton or a Widmer column may, of course, be used. 

All the products of Clemmensen reductions contain small amounts of un-saturated hydrocarbons. These can be removed by repeated shaking with 10 per cent, of the volume of concentrated sulphuric acid until the acid is colourless or nearly so each shaking should be of about 5 minutes duration. The hydrocarbon is washed with water, 10 per cent, sodium carbonate solution, water (twice), dried with anhydreus magnesium or calcium sulphate, and finally distilled twice from a Claisen flask with fractionating side arm (or a Widmer flask) over sodium. 

A Widmer column (spiral 18 cm. in length, 1 5 cm. in diameter with 20 turns of the helix) is satisfactory. 

In a 200 ml. distilling flask place 64 g. (50 ml.) of dry n-butyl bromide and 80 g. of dry silver nitrite (1). Insert a reflux condenser, carrying a cotton wool (or calcium chloride) guard tube, into the mouth of the flask and close the side arm with a small stopper. Allow the mixture to stand for 2 hours heat on a steam bath for 4 hours (some brown fumes are evolved), followed by 8 hours in an oil bath at 110°. Distil the mixture and collect the fraction of b.p. 149-151° as pure 1-nitro-n-butane (18 g.). A further small quantity may be obtained by distilling the fractions of low boihng point from a Widmer flask. 

Finally distil from a well-lagged Widmer flask (compare Figs. II, 24, 2-5) over a little sodium. Collect the cycZo hexyl ethyl ether at 148-150°. The yield is 21 g. If the sodium is appreciably attacked, repeat the distillation from a fresh quantity of sodium. 

Pour the reaction mixture cautiously into 400 g. of crushed ice and acidify it in the cold by the addition of a solution prepared by adding 55 ml. of concentrated sulphuric acid to 150 ml. of water and then coohng to 0°. Separate the ether layer and extract the aqueous layer twice with 50 ml. portions of ether. Dry the combined ethereal solutions over 50 g. of anhydrous potassium carbonate and distil the filtered solution thror h a Widmer column (Figs. II, 17, 1 and II, 24, 4). Collect separately the fraction boihng up to 103°, and the dimethylethynyl carbinol at 103-107° Discard the high boiling point material. Dry the fraction of low boihng point with anhydrous potassium carbonate and redistil. The total 3 ield is 75 g. 

Make a thin paste of 21 5 g. of finely-powdered o-tolidine (a commercial product) with 300 ml. of water in a 1-litre beaker, add 25 g. (21 ml.) of concentrated hydrochloric acid, and warm until dissolved. Cool the solution to 10° with ice, stir mechanically, and add a further 25 g. (21 ml.) of concentrated hydrochloric acid (1) partial separation of o tolidine dihydrochloride will occur. Add a solution of 15 g, of sodium nitrite in 30 ml. of water as rapidly as possible, but keep the temperature below 15° a slight excess of nitrous acid is not harmful in this preparation. Add the clear, orange tetrazonium solution to 175 ml. of 30 per cent, hypophosphorous acid (2), and allow the mixture to stand, loosely stoppered, at room temperature for 16-18 hours. Transfer to a separatory funnel, and remove the upper red oily layer. Extract the aqueous layer with 50 ml, of benzene. Dry the combined upper layer and benzene extract with anhydrous magnesium sulphate, and remove the benzene by distillation (compare Fig. II, 13, 4) from a Widmer or similar flask (Figs. II, 24, 3-5) heat in an oil bath to 150° to ensure the removal of the last traces of benzene. Distil the residue at ca. 3 mm. pressure and a temperature of 155°. Collect the 3 3 -dimethyldiphenyl as a pale yellow liquid at 114-115°/3 mm. raise the bath temperature to about 170° when the temperature of the thermometer in the flask commences to fall. The yield is 14 g. 

Methyl y-bromocrotonate. Mix 36 g. of iV-bromosuccinimide, 40 g. of methyl crotonate and 60 ml. of dry, redistilled carbon tetrachloride in a 500 ml. round bottomed flask. Reflux ou a water bath for 12 hours by this time all the sohd should have risen to the surface of the liquid. Filter off the succinimide at the pump and wash it with a little dry carbon tetrachloride. Remove the solvent on a water bath and distil the residue under reduced pressure, preferably from a Widmer flask (compare Figs. II, 24, 4-5). Collect the methyl y-bromocrotonate at 77-78°/8 mm. the yield is 31 g. 

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. 

Widmer column. The remaining liquid was also distilled at normal pressure, using... 

A solution of (CH3)3C-CH=C=CLi, obtained by addition at -60°C of 0.20 mol of tert.-butylallene (see Chapter VI, Exp. 2) to a solution of 0.25 mol of ethyllithium in about 200 ml of diethyl ether (see Chapter II, Exp. 1) was warmed to 25°C and held at this temperature for 15 min. Subsequently the solution was cooled to below 0°C and 50 ml of saturated NH,C1 solution were added dropwise with vigorous stirring, keeping the temperature below 2o C. The upper layer v as separated off and the aqueous layer was extracted twice with 25-ml portions of diethyl ether. The combined solutions were dried over a small amount of magnesium sulfate. Slow distillation through a 40-cm Widmer column gave neopentyl acetylene (b.p. 76°C/750 mmHg, 20... 

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