Drying agent potassium carbonate

The two-phase mixture is placed in a separatory funnel, and the heavy red-brown oil is separated. The aqueous phase is extracted with 100 ml. of ether. The oil and the ether extract are combined, washed with 50 ml. of saturated sodium chloride, and dried over potassium carbonate. The drying agent is removed by filtration, and the filtrate is distilled. Colorless 2-bromoallyl-amine is collected at 65-68°/100 mm. weight 49-59 g. (59-72%) 1.5075-1.5085 (Note 6). 

Dimethyl-2-oxazoline is commercially available from Columbia Organic Chemicals, 912 Drake Street, Columbia, South Carolina, or may be prepared as follows. In a 250-ml., three-necked flask is placed 89.14 g. (1.0 mole) of 2-amino-2-methyl-l-propanol, and the flask is cooled in an ice bath. The amine is carefully neutralized with 52.3 g. (1.0 mole) of 90.6% formic acid over a 1-hour period. A magnetic stirring bar is added, the flask is fitted with a short path distillation head, and the reaction mixture is placed in a silicon oil bath which is rapidly heated to 220-250°. The azeotropic mixture of water and oxazoline distills over a period of 2-4 hours and is collected in an ioe-cooled flask containing ether. The aqueous layer is separated, saturated with sodium chloride, and extracted with three 50-ml. portions of ether. The combined ethereal extracts are dried over potassium carbonate, filtered to remove the drying agent, and the ether is removed at 35-40° at atmospheric pressure. The 4,4-dimethyl-2-oxazoline is collected as the temperature rises above 85°. The yield is 56.7-62.7 g. (57—63%) of a colorless mobile liquid, b.p. 99-100° (758 mm. Hg). 

Anhydrous sodium sulphate, even when freshly ignited before use, is much less active than calcium chloride. It is used when a substitute for calcium chloride is indicated for the reasons given above. For solutions of basic substances ignited potassium carbonate, solid potassium hydroxide, and barium oxide are much used as drying agents. 

C. (R,R)-N,N -Bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine. A 2-L, three-necked, round-bottomed flask equipped with a mechanical overhead stirrer, reflux condenser, and an addition funnel is charged with 29.7 g of (R,R)-1,2-diammoniumcyclohexane mono-(+)-tartrate salt (0.112 mol), 31.2 g of potassium carbonate (0.225 mol, 2 eq), and 150 mL of water. The mixture is stirred until dissolution is achieved, and 600 mL of ethanol is added. The cloudy mixture is heated to reflux with a heating mantle and a solution of 53.7 g (0.229 mol, 2.0 eq) of 3,5-di-tert-butylsalicylaldehyde in 250 mL of ethanol is then added in a slow stream over 30 min (Note 19). The addition funnel is rinsed with 50 mL of ethanol and the mixture is stirred at reflux for 2 hr before heating is discontinued. Water, 150 mL, is added and the stirred mixture is cooled to <5°C over 2 hr and maintained at that temperature for another hour. The yellow solid is collected by vacuum filtration and washed with 100 mL of ethanol. After the solid is air dried, it is dissolved in 500 mL of methylene chloride. The organic solution is washed with 2 x 300 mL of water, followed by 300 mL of saturated aqueous sodium chloride. The organic layer is dried over sodium sulfate, and filtered to remove the drying agent. The solvent is removed by rotary evaporation to yield the product as a yellow solid, mp 200-203°C (Notes 20 and 21). 

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). 

The physical constants of several other imines prepared by a similar procedure are shown in Table X. The aldimines listed in the Table can be obtained only if certain precautions are strictly observed [4b]. The method of Emerson, Hess, and Uhle [4c] could not be extended satisfactorily and the method described in Preparation 2-2 is a modification of the one described by Chancel [4d] for propylidenepropylamine. The reaction is best carried out by adding the aldehyde to the amine, without a solvent, at 0°C. When the order of addition is reversed, the yields are much lower. Potassium hydroxide is added at the end in order to remove the water formed during the reaction. The use of other drying agents such as potassium carbonate or magnesium sulfate failed to yield aldimines on distillation. The aldimines should always be distilled from fresh potassium hydroxide to yield water-white products. The aldimines are unstable and should be used within a few hours after their distillation otherwise polymeric products are obtained. 

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