Pressure Widmer

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. 

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

Widmer column gave butylallene, b.p. 105 C/760 mmHg, n 1.4332. The remaining liquid was distilled in a partial vacuum (60-100 mmHg, b.p. 40-70°C) and the distillate was redistilled at normal pressure to give an additional amount of butylallene, bringing the yield to 72-78%. 

The crude ester may be used directly in the preparation of serine. However, greater ease of purification and slightly better yields make it advantageous to prepare the free acid. Pure methyl a-bromo-j8-methoxypropionate is obtained by fractionally distilling the crude material under reduced pressure through a Widmer column. From 100 g. of crude material there is obtained 80-90 g. of pure ester, b.p. 73-75°/6 mm., n 1.4586. 

The 1-alkynyl (0.55 mole) is added in 5 min to a solution of 0.50 mole of lithium dialkylamide in 500 ml of ether at room temperature. The ether is removed by distillation and an exothermic reaction starts at a bath temperature of about 80°C. Heating is continued for an additional 30 min at 110°-120°C and then the reaction products are distilled at 15 mm Hg pressure using a short Vigreux column. The heating bath is raised to 170°C and the last traces of products are removed by distillation at 1 mm Hg pressure. In all cases the distillation receiver should be cooled to —80°C. The entire distillates are combined and fractionated through a 30 cm Widmer column. Some typical results of using this method are shown in Table II. 

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