Distillation under diminished pressure

Claisen flask or Claisen flask with fractionating side arm, see Figs. II, 13, (i and II, 13, 5, may be used, particularly if the residue is to be ultimately distilled under diminished pressure) should have a capacity of about twice the estimated volume of the residue after the removal of the solvent. The adapter may be omitted, if desired, and the end of the... 

DISTILLATION UNDER DIMINISHED PRESSURE ( VACUUM DISTILLATION)... 

Distillation of solids under reduced pressure.—The apparatus shown in Fig. II, 19, 1 may be employed for the distillation under diminished pressure of solids possessing comparatively low melting points ... 

The maintenance of a constant pressure in a system during distillation under diminished pressure is of great practical importance if trustworthy boiling points are desired. Devices which maintain a constant pressure in a system that is higher than the minimum pressure that the pump will give are termed manostats. A simple manostat, due to M. S. Newman, is illustrated in Fig. II, 23, 4. 

A criticism that is sometimes levelled at distillation under diminished pressure when rubber stoppers are used is that contact of the hot vapour with the rubber frequently contaminates the distillate. In the author s... 

An elementary account of the subject has been given in the previous Section. For the fractional distillation under diminished pressure of liquids diflfering only slightly in boiling point, a firactionating column (see Sections 11,15 and 11,17) must be used. Provision must, of course, be made for the insertion of a capillary tube into the fiask containing the mixture. This can be done by any of the following methods —... 

Fit up the apparatus shown in Fig. Ill, 31, 1 the capacity of the Claisen flask should be 100 ml. Place 40 g. (24-6 ml.) of redistilled thionyl chloride in the flask and 60 g. (62 ml.) of dry n-butyl alcohol (b.p. 116-117°) in the dropping funnel. Cool the flask in ice and add the n-butyl alcohol, with frequent shaking, over 1 hour (1). Reflux the mixture gently for 1 hour to complete the reaction and to remove the residual hydrogen chloride. Arrange the apparatus for distillation, and distil under normal pressure until the temperature rises to 120° then distil under diminished pressure (Fig. 11, 20, 1) and collect the di-n-butyl sulphite at 116-118°/20 mm. The yield is 66 g. 

Nitro-n-hexane. Use 41 g. of dry silver nitrite, 51 g. of n-hexyl iodide (35-5 ml.) and 100 ml. of sodium dried ether. Reflux on a water bath for 8 hours decant the ethereal solution and wash the sohd well with sodium dried ether. Distil the residue, after the removal of the ether from the combined extracts, from 5 g. of dry silver nitrite, and collect the fraction of b.p. 190-192° (13 g.) as 1-nitro -hexane. The pure compound is obtained by distilling under diminished pressure b.p. 81 6°/15 mm. 

The residue (220 g.) crystallises on coohng and consists of almost pure monobromoacetic acid (2). If it is required perfectly pure, distil the crude acid from a Claisen flask and collect the fraction of b.p. 202-204°. When distilled under diminished pressure, the acid boils at 117-118°/ 5 mm. Pure monobromoacetic acid has m.p. 50°,... 

Vinylacetic acid. Place 134 g. (161 ml.) of allyl cyanide (3) and 200 ml. of concentrated hydrochloric acid in a 1-htre round-bottomed flask attached to a reflux condenser. Warm the mixture cautiously with a small flame and shake from time to time. After 7-10 minutes, a vigorous reaction sets in and the mixture refluxes remove the flame and cool the flask, if necessary, in cold water. Ammonium chloride crystallises out. When the reaction subsides, reflux the mixture for 15 minutes. Then add 200 ml. of water, cool and separate the upper layer of acid. Extract the aqueous layer with three 100 ml. portions of ether. Combine the acid and the ether extracts, and remove the ether under atmospheric pressure in a 250 ml. Claisen flask with fractionating side arm (compare Fig. II, 13, 4) continue the heating on a water bath until the temperature of the vapour reaches 70°. Allow the apparatus to cool and distil under diminished pressure (compare Fig. II, 20, 1) , collect the fraction (a) distilling up to 71°/14 mm. and (6) at 72-74°/14 mm. (chiefly at 72 5°/ 14 mm.). A dark residue (about 10 ml.) and some white sohd ( crotonio acid) remains in the flask. Fraction (6) weighs 100 g. and is analytically pure vinylacetic acid. Fraction (a) weighs about 50 g. and separates into two layers remove the water layer, dry with anhydrous sodium sulphate and distil from a 50 ml. Claisen flask with fractionating side arm a further 15 g. of reasonably pure acid, b.p. 69-70°/12 mm., is obtained. 

This is an alternative experiment to the actual preparation of the ester and will give the student practice in conducting a distillation under diminished pressure. Commercial ethyl acetoacetate generally contains inter alia some ethyl acetate and acetic acid these are removed in the following procedure. 

Into a 500 nil. round-bottomed flask, provided with a double surface condenser, place 50 g. (63 ml.) of pure, dry acetone, 50 g. (47 ml.) of ethyl cyanoacetate (Section 111,131) and 0 -5 g. of piperidine. Allow to stand for 60 hours and heat on a water bath for 2 hours. Treat the cold reaction mixture with 100 ml. of ether, wash with dilute hydrochloric acid, then with water, and dry over anhydrous sodium or magnesium sulphate. Distil under diminished pressure and collect the ethyl fsopropylidene cyanoacetate (ethyl a-cyano-pp-dimethylacrylate) at 114-116°/14mm.(l). The yield is 39 g. 

To obtain optically pure I- and daec.-octyl alcohols, steam distil the respective esters with 30 per cent, sodium hydroxide solution use the proportions 1 mol of ester to 2 mols of sodium hydroxide. Separate the alcohols from the steam distillate, dry over anhydrous potassium carbonate, and distil under diminished pressure. Both samples boU at 86°/20 mm. (9) and have the following rotations ... 

The crude substance may also be distilled under diminished pressure and the p-tolunitrile collected at 104-106 /20 uun. 

I) When working with larger quantities of material, it is more convenient (and a better yield is obtained) to purify the air-dried product by distillation under diminished pressure. Use the apparatus pictured in Fig. II, 19, 4, and add a few fragments of porous porcelain to the solid. No air inlet can be employed to prevent bumping since this may lead to explosive decomposition. Collect the pure m-nitrophenol at I60-I65°/I2 mm. always allow the flask to cool before admitting air otherwise the residue may decompose with explosive violence. The recovery is over 90 per cent, of the pure m-nitroplienol. 

The ester and catalj st are usually employed in equimoleciilar amounts. With R =CjHs (phenyl propionate), the products are o- and p-propiophenol with R = CH3 (phenyl acetate), o- and p-hydroxyacetophenone are formed. The nature of the product is influenced by the structure of the ester, by the temperature, the solvent and the amount of aluminium chloride used generally, low reaction temperatures favour the formation of p-hydroxy ketones. It is usually possible to separate the two hydroxy ketones by fractional distillation under diminished pressure through an efficient fractionating column or by steam distillation the ortho compounds, being chelated, are more volatile in steam It may be mentioned that Clemmensen reduction (compare Section IV,6) of the hj droxy ketones affords an excellent route to the substituted phenols. 

Concentrate the mother liquors from this recrystallisation and combine with the oily filtrate dissolve in 250 ml. of 10 per cent, sodium hydroxide solution, and extract with two 50 ml. portions of ether to remove non-phenolic products. Acidify the alkaline solution with hydrochloric acid, separate the oily layer, dry it over anhydrous magnesium sulphate, and distil under diminished pressure, preferably from a Claisen flask with fractionating side arm (Figs. II, 24, 2-5). Collect the o-propiophenol (65 g.) at 110-115°/6 mm. and a further quantity (20 g.) of crude p-propiophenol at 140-150°/ 1 mm. 

Decant the ethereal solution from the yellow aldimine stannichloride which has separated, rinse the solid with two 50 ml. portions of ether, and transfer the solid to a 2-5 litre flask fitted for steam distillation and immersed in an oil bath at 110-120°. Pass steam through a trap (compare Fig. 11,40, 1,6) to remove condensed water, then through a superheater heated to 260° (Fig. I, 7, 2), and finally into the mixture (2). Continue the passage of y steam until the aldehyde is completely removed (4-5 litres 8-10 hours). Filter the white soUd at the pump, and dry in the air. The resulting p-naphthaldehyde, m.p. 53-54°, weighs 12 g. It may be further purified by distillation under diminished pressure (Fig. II, 19, ) -, pour the colourless distillate, b.p. 156-158°/15 mm., while hot into a mortar and powder it when cold. The m.p. is 57- 58°, and the recovery is over 90 per cent. 

Y-Phenylbutyric acid. Prepare amalgamated zinc from 120 g. of zinc wool contained in a 1-litre rovmd-bottomed flask (Section 111,50, IS), decant the liquid as completely as possible, and add in the following order 75 ml. of water, 180 ml. of concentrated hydrochloric acid, 100 ml. of pure toluene (1) and 50 g. of p benzoylpropionic acid. Fit the flask with a reflux condenser connected to a gas absorption device (Fig. II, 8, l,c), and boil the reaction mixture vigorously for 30 hours add three or four 50 ml. portions of concentrated hydrochloric acid at approximately six hour intervals during the refluxing period in order to maintain the concentration of the acid. Allow to cool to room temperature and separate the two layers. Dilute the aqueous portion with about 200 ml. of water and extract with three 75 ml. portions of ether. Combine the toluene layer with the ether extracts, wash with water, and dry over anhydrous magnesium or calcium sulphate. Remove the solvents by distillation under diminished pressure on a water bath (compare Fig. II, 37, 1), transfer the residue to a Claisen flask, and distil imder reduced pressure (Fig. II, 19, 1). Collect the y-phenylbutyric acid at 178-181°/19 mm. this solidifies on coohng to a colourless sohd (40 g.) and melts at 47-48°. 

Preparation of benzyl cyanide. Place 100 g. of powdered, technical sodium cyanide (97-98 per cent. NaCN) (CAUTION) and 90 ml. of water in a 1 litre round-bottomed flask provided with a reflux condenser. Warm on a water bath until the sodium cyanide dissolves. Add, by means of a separatory funnel fitted into the top of the condenser with a grooved cork, a solution of 200 g. (181-5 ml.) of benzyl chloride (Section IV.22) in 200 g. of rectified spirit during 30-45 minutes. Heat the mixture in a water bath for 4 hours, cool, and filter off the precipitated sodium chloride with suction wash with a little alcohol. Distil off as much as possible of the alcohol on a water bath (wrap the flask in a cloth) (Fig. II, 13, 3). Cool the residual liquid, filter if necessary, and separate the layer of crude benzyl cyanide. (Sometimes it is advantageous to extract the nitrile with ether or benzene.) Dry over a little anhydrous magnesium sulphate, and distil under diminished pressure from a Claisen flask, preferably with a fractionating side arm (Figs. II, 24, 2-5). Collect the benzyl cyanide at 102-103°/10 mm. The yield is 160 g. 

Distillation under diminished pressure.— A simple apparatus is illustrated in Fig. XII, 2, 7. The Claisen flask with pear-shaped bulb is... 

Fractional distillation under diminished pressure.—A 5-25 ml. Claisen flask (with pear-shaped bulb) provided with a fractionating side arm (Fig. II, 24, 4r-5) and attached to a Liebig s condenser and a Perkin triangle (Fig. II, 20, 1 or II, 20, 2 volume of receiver ca. 10 ml.) wUl be found to have wide apphcation. 

The stirrer is started and there is added rapidly a cold sulfuric acid solution made by adding enough ice to 200 cc. of concentrated sulfuric acid (sp. g. 1.84) (Note 7) so that some of the ice is not melted. The stirring is continued for five or ten minutes or until the yellow lumps of the sodium salt disappear. The mixture is then extracted with three 600-cc. portions of benzene (Note 8). The benzene is destilled (Note g) from the extracts on a water bath and the residue is transferred to a special 2-I. Claisen flask (Org. Syn. 1, 40) and distilled under diminished pressure. The product boils at i3o-i32°/37 mm. or ii7-iig°/2g mm. A small high-boiling fraction is redistilled to yield 20-30 g. more of the ethyl acetopyruvate. The total yield is 480-520 g. (61-66 per cent of the theoretical amount). 

When extraction is complete the ether solution of 2-furylcarbinol is distilled until the temperature of the liquid (not the vapor) reaches 95°. Then the residue is distilled under diminished pressure. Some ether and water come over first and the temperature then rises rapidly to the boiling point of 2-furylcarbinol. The yield of 2-furylcarbinol boiling at 75-77°/iS mm. is 310-325 g. (61-63 psr cent of the theoretical amount) (Note 5). 

Phenylethylene should not be distilled under atmospheric pressure since the temperature (146°) required for the distillation causes a considerable loss by polymerization. The decomposition of cinnamic acid cannot be effected by distillation under diminished pressure, since the acid under these conditions distils below the temperature required for decomposition (approxi-natcly 300°). 

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