Boiling constant

In a 1-litre three-necked flask, mounted on a steam bath and provided respectively with a separatory funnel, mechanical stirrer and double surface condenser, place 165 g. of bromoform (96 per cent.). Add 10 ml. of a solution of sodium arsenite made by dissolving 77 g. of A.R. arsenious oxide and 148 g. of A.R. sodium hydroxide in 475 ml. of water. Warm the mixture gently to start the reaction, and introduce the remainder of the sodium arsenite solution during 30-45 minutes at such a rate that the mixture refluxes gently. Subsequently heat the flask on the steam bath for 3-4 hours. Steam distil the reaction mixture (Fig. 11, 41, 1) and separate the lower layer of methylene bromide (79 g.). Extract the aqueous layer with about 100 ml. of ether a further 3 g. of methylene bromide is obtained. Dry with 3-4 g. of anhydrous calcium chloride, and distil from a Claisen flask with fractionating side arm. The methylene bromide boils constantly at 96-97° and is almost colourless. 

C. N-Hydroxy-4-(p-chlorophenyl)thiazole-2(3H)-thione. O-Ethyl S-[2-oximino-2-(p-chlorophenyl)ethyl]dithiocarbonate (56.0 g, 0.19 mol) is placed in a 500-mL round-bottomed flask that is equipped with a magnetic stir bar. Diethyl ether (120 mL) is added and the slurry is treated at 0°C in small portions with solid anhydrous zinc chloride, ZnClj, 79.1 g, 0.58 mol) at such a rate that the solvent does not boil constantly (Note 8). After the addition is complete, the flask is stoppered with a drying tube (CaCl2) and stirring is continued for 48 hr at 20°C. The reaction mixture turns into a dear, dark brown solution that solidifies toward the end of the reaction. The flask is immersed in an ice bath and treated dropwise with 5.5 M hydrochloric add (140 mL, Note 9). The precipitate dissolves immediately. Stirring is continued for 30 min at 0°C whereupon a tan-colored solid separates. This material is collected by filtration. It is washed with small portions of diethyl ether (total of 110 mL) and dried to afford 39.8 g (86%) of N-hydroxy-4-(p-chlorophenyl)thiazole-2(3H)-thione (Note 10). The crude material is transferred to a 2-L, round-bottomed flask equipped with a reflux condenser. 2-Propanol (760 mL) is added and the reaction mixture is heated to reflux. Once a dear solution is obtained the heat source is immediately removed (Note 11). The solution is allowed to cool to room temperature. Precipitation of N-hydroxy-4-(p-chlorophenyl)thiazole-2(3H)-thione is completed by immersing the flask for 30 min in an acetone-dry ice bath (-78°C). The product is collected by filtration and dried to afford 21.9 g (53.5%) of N-hydroxy-4-(p-chlorophenyl)thiazole-2(3H)-thione as tan crystals (Notes 12,13). 

Addition of ZnClj is exothermic. The reaction mixture may bubble upon addition of each portion of ZnCl2, but it should not boil constantly. After addition of ZnClj is complete, a 4.8-5 M solution of ZnClj is obtained that leads to a maximum yield of the title... 

Another boiling point is 66-68°/6 mm. If the product is distilled through a short column (12-15 cm.) packed with glass helices, it boils constantly at 98°/22 mm. The recovery is somewhat lower when a column is used. 

The hydrogen bromide was passed into 50 ml. of technical thionyl chloride for 12 hours at 0°C., yielding a reddish liquid which on distillation under diminished pressure in an all-glass apparatus gave 50 ml. of an orange-red liquid, boiling constantly at 69 to 70°C. at 62 mm. On redistillation, the product boiled at 48°C. at 20 mm. and was orange-yellow in color. 

The gaseous hydriodic acid is an intensely fuming substance, which may be easily shown by removing the cork from the receiver containing the aqueous acid, for a moment. Hydriodic acid is absorbed by water with great aridity. The acid, boiling constantly at 1270, contains approximately 50% of anhydrous hydriodic acid. 

When a mixture of alcohol and water is distilled, the liquid will not boil constantly at 173 F. until all the alcohol has passed over, but will rise in temperature gi adnally throughout the distillation until 212 F. have been reached. The distillate, if separated into fractions boiling between fixed points, consists of a series of mixtures of alcohol and water in definite proportions. Tlie mixtures richest in alcohol come over first that Is to say. at the lowest temperature. 

Relative permittivity (dielectric constant) A measure of the reduction of the potential energy of interaction between the charges on going from vacuum to a medium (such as gas or hquid). The dimensionless relative permittivity of a substance is measured by comparing the capacitance of a capacitor with (C) and without (Cg) the sample present, according to = C/Cg. The name dielectric constant is a misnomer because it is indeed not a constant each solvent has its own value. For example, melting constant or boiling constant are not used. 

Whilst at the ordinary atmospheric pressure (760 mm. mercury) the glycerine boils constantly at 290° C., boiling takes place, at a pressure cf 500 mm. mercury, already at 210° C. when one has a pressure of only 12.5 mm., then glycerine boils at 179-o° and it is therefore advisable to provide the distillation apparatus with, a very strongly acting air-pump, so that a very low pressure can be obtained. By adequate influx cf steam the boiling then takes place very quickly, and the distillation is completed in a very short time. 

---