Air bath

The advantages of the above air bath are (1) simplicity and cheapness of construction (2)ease of temperature control (3) rapidity of cooling of the contents of the flask effected either by removing the asbestos covers or by completely removing the air bath and (4) the contents of the flask may be inspected by removing the asbestos covers. 

The theory of the process is discussed in Sections 1,1-1,3. The apparatus of Fig. 11,12,1 may be used when moderate quantities of the substance are available. A is a 50 ml. distilling flask attached by a cork to a Liebig condenser B, upon the end of which an adapter C is fitted D is a receiver for collecting the distillate. The thermometer E is fitted into the neck of the distilling flask by means of a well-bored cork the bulb of the thermometer should be in the centre of the neck of the flask and slightly below (ca. 5 mm.) the level of the side tube. The flask may be heated on a wire gauze with asbestos centre or preferably in an air bath (Fig. 77, 5, 3). 

It must be borne in mind that in spite of the fact that the solvents have normal boiling points below 90-95°, they cannot always be completely removed by heating on a steam or water bath when they form part of mixtures with less-volatile liquids. Simple distillation may lead to mixtures with higher boiling points than the individual solvents, so that separation of the latter may not be quite complete. In such cases the distillation should be completed with the aid of an air bath (Fig. 77,5,3) or an oil bath the Are hazard is considerably reduced since most of the solvent will have been removed. 

Solvents with boiling points above 90-95°. The apparatus of Fig. 77,13, 3 (with closed filter flask and rubber lead-off tube) or of Fig. 77,13, 4 (see discussion in previous paragraph but one) should be vtilised vrith an air bath or oil bath as the source of heat. Heating on a Wire gauze is not recommended. 

Oleum is marketed in all strengths up to ca. 70 per cent. SO3. From 0 to 40 per cent, free SO3, it is a liquid from 40 to 60 per cent, free SO3, it is a solid from 60 to 70 per cent, free SO3, it is liquid above 70 per cent, free SO3, it is a solid. The acid must be kept in ground glass stoppered, thick-walled bottles. If it is required to melt the acid, the stopper is removed, a watch glass placed on the mouth of the bottle, and the bottle placed in a layer of sand in an air bath which is warmed with a small flame. The bottle is fitted with a wash bottle attachment, and any desired quantity of acid is forced out by gentle air pressure from a hand or foot bellows (the mouth must not be used) this procedure is far more satisfactory than that of pouring the liquid acid from the bottle. 

Zinc cyanide. Solutions of the reactants are prepared by dis solving 100 g. of technical sodium cyanide (97-98 per cent. NaCN) in 125 ml. of water and 150 g. of anhydrous zinc chloride in the minimum volume of 50 per cent, alcohol (1). The sodium cyanide solution is added rapidly, with agitation, to the zinc chloride solution. The precipitated zinc cyanide is filtered off at the pump, drained well, washed with alcohol and then with ether. It is dried in a desiccator or in an air bath at 50°, and preserved in a tightly stoppered bottle. The yield is almost quantitative and the zinc cyanide has a purity of 95-98 per cent. (2). It has been stated that highly purified zinc cyanide does not react in the Adams modification of the Gattermann reaction (compare Section IV,12l). The product, prepared by the above method is, however, highly satisfactory. Commercial zinc cyanide may also be used. 

For successful fractional distillation, slow and even heating of the bath surrounding the flask is essential. This may be achieved by suitably designed electrically-heated air baths or by the use of oil baths provided... 

Sulphuric acid method. Place 20 g. of commercial cycZohexanol and 0-6 ml. of concentrated sulphuric acid in a 150 or 200 ml. round-bottomed or bolt head flask, add 2-3 chips of porous porcelain, and mix well. Fit the flask with a fractionating column, a Liebig condenser, adapter and filter flask receiver as in Section 111,10 (1). Heat the flask in an air bath (Fig. II, 5, 3) at such a rate that the temperature at the top of the column does not rise above 90° alternatively, an oil bath, heated to a temperature of 130-140°, may be used. Stop the distillation when only a small residue remains and the odour of sulphur dioxide is apparent. Transfer the distillate to a small separatory funnel. 

Filter the dried product through a fluted filter paper or a small cotton wool plug supported in a funnel into a dry 50 ml. distilling flask, and distil on a wire gauze or from an air bath (Fig. 11, 5, 3). Collect the fraction, b.p. 100-103°. The yield of n-butyl bromide is 18-19 g. 

Mix 30 g. (38 ml.) of iaopropyl alcohol with 450 g. (265 ml.) of constant boiling point hydriodic acid (57 per cent.) (Section 11,49,2) in a 500 ml. distilling flask, attach a condenser for downward distillation, and distil slowly (1-2 drops per second) from an air bath (compare Fig. II, 5, 3). When about half the liquid has passed over, stop the distillation. Separate the lower layer of crude iodide (80 g.). Redistil the aqueous layer and thus recover a further 5 g. of iodide from the flrst quarter of the distillate (1). Wash the combined iodides with an equal volume of concentrated hydrochloric acid, then, successively, with water, 5 per cent, sodium carbonate solution, and water. Dry with anhydrous calcium chloride and distil. The isopropyl iodide distils constantly at 89°. 

Methyl ethyl ketone. Use the apparatus of Fig. Ill, 61, 1 but with a 500 ml. round-bottomed flask. Place 40 g. (50 ml.) of see. butyl alcohol, 100 ml. of water and a few fragments of porous porcelain in the flask. Dissolve 100 g. of sodium dichromate dihydrate in 125 ml. of water in a beaker and add very slowly and with constant sturing 80 ml. of concentrated sulphuric acid allow to cool, and transfer the resulting solution to the dropping funnel. Heat the flask on a wire gauze or in an air bath until the alcohol mixture commences to boil. Remove the flame and run in the dichromate solution slowly and at such a rate that the temperature... 

Pour the reaction mixture into a 1-litre round-bottomed flaak, add 250 ml. of water, fit a still head and a condenser for downward distillation (Fig. II, 13, 3, but without the thermometer). Distil the mixture until about 125 ml. of distillate (two layers) have been collected. Saturate with salt (about 30 g. are required), and separate the upper layer of cj/cZohexanone extract the aqueous layer with 25-30 ml. of ether and combine the ether extract with the cycZohexanone layer. Dry with about 6 g. of anhydrous sodium or magnesium sulphate, filter the solution into a distilling flask of suitable size to which a condenser has previously been attached. Distil oflF the ether from a water bath—a beaker containing warm water is satisfactory. Distil the residual liquid from an air bath or a wire gauze, and collect the cyclohexanone at 153-156°. The yield is 16 g. 

Mix 200 g. of adipic acid intimately with 10 g. of finely-powdered, crystallised barium hydroxide. Place the mixture in a 1-litre distilling flask, fitted with a thermometer reaching to within 5 mm. of the bottom connect the flask with a condenser and receiver. Heat the mixture gradually in an air bath (1) to 285-295° during about 90 minutes and maintain it at this temperature mitil only a small amount of dry residue remains in the flask this requires a further 2 hours. The temperature must not be allowed to rise above 300°, since at this temperature the adipic acid distils quite rapidly the best working temperature is 290°. The cycZopentanone distils slowly accompanied by a little adipic acid. Separate the ketone from the water in the distillate, and dry it with anhydrous potassium carbonate this treatment simultaneously removes the traces of adipic acid present. Finally distil from a flask of suitable size and collect the cycZopentanone at 128-131°. The yield is 92 g. 

Fit a 750 ml. round-bottomed flask with a fractionating column attached to a condenser set for downward distillation. Place 500 g. of diacetone alcohol (the crude product is quite satisfactory), 01 g. of iodine and a few fragments of porous porcelain in the flask. Distil slowly. with a small free flame (best in an air bath) and collect the following fractions (a) 56-80° (acetone and a little mesityl oxide) (6) 80-126° (two layers, water and mesityl oxide) and (c) 126-131° (mesityl oxide). Whilst fraction (c) is distilling, separate the water from fraction (6), dry with anhydrous potassium carbonate or anhydrous magnesium sulphate, and fractionate from a small flask collect the mesityl oxide at 126-131°. The yield is about 400 g. 

Mix 100 g. of maleic acid (Section 111,143) and 100 ml. of tetra chloroethane in a 250 ml. Claisen or distilling flask provided with a thermometer, and attach a Pyrex Liebig condenser. Heat the flask in an air bath (Fig. 11, 5, 3) and collect the distillate in a measuring cylinder. When the temperature reaches 160°, 76 ml. of tetrachloroethane and 15-15-5 ml. of water are present in the receiver. Empty the water in the condenser and continue the distillation change the receiver when the temperature reaches 190°. Collect the maleic anhydride at 195-197°. Recrystallise the crude anhydride from chloroform. The yield of pure maleic anhydride, m.p. 54°, is 70 g. 

Fit a reflux condenser into the short neck of a 125 ml. Claisen flask, a separatory funnel into the long neck, and plug the side arm with a small cork (compare Fig. Ill, 31, 1). Place 58 g. (62 ml.) of commercial n-caproic acid (1) in the flask and heat on a water hath. Add 75 g. (46 ml.) of redistilled thionyl chloride through the separatory funnel during 45 minutes shake the flask from time to time to ensure thorough mixing. Reflux the mixture for 30 minutes. Arrange the apparatus for distillation from an air bath (Fig. II, 5, 3) the excess of thionyl chloride passes over flrst, followed by n-caproyl chloride at 145-155° (mainly at 150-155°). The yield of acid chloride is 56 g. 

Place 29 g. of n-caproamide (Section 111,109) into a 200 ml. distilling flask, and assemble the apparatus shown in Fig. Ill, 28, 1. Remove the trap momentarily and introduce 45 g. (27-5 ml.) of redistilled thionyl chloride no apparent reaction takes place in the cold. Warm the mixture on a water bath or by means of a small flame for 1 hour. Arrange the apparatus for distillation and distil oflF the excess of thionyl chloride (t.c., until the temperature reaches about 90°) and allow to cool. When cold, transfer the residue to a 100 ml. distilling flask (1). Distil from an air bath (Fig. II, 5, 3) the n-capronitrile passes over at 161-163° (2). The yield is 21 g. 

Transfer the reaction product to a 500 ml. Claisen flask and distil over a wire gauze or from an air bath. Some acetyl chloride and acetic acid passes over first, the temperature then rises, and the fraction, b.p. 150-200°, is collected separately run out the water from the condenser when the temperature reaches 150°. The fraction, b.p. 150-200°, solidifies on cooling. Drain off any hquid from the crystals as rapidly as possible, and redistil the solid using an air condenser. CoUect the fraction b.p. 182-192° this sets to a sohd mass on cooling and melts at 63°. The yield of monochloroacetic acid is 150-175 g. 

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