Isolation distillation

Thus 1 78 g (1.186 mole) of pure piperonal is isolated distilling at 106° C. under a vacuum of 2.4 mbars and having a melting point of 37°+l°C. The yield is established at 79% of the theoretically calculated value relative to the 3,4-methylenedioxy mandelic acid used. 

Reductive cyclization of the esters 72 and 74 provides the 3,4-dioxo compound 73 and the 4-oxo derivatives 75. The reductions are performed using hydrogen over platinum in acetic acid. If milder conditions are used, the intermediates 76 to the 4-oxo compounds can be isolated. " Distillation then affords the cyclized products 75. 

Figure 11-5. Heat exchange for an isolated distillation column...

Separation of classes of components. If a class of components is to be separated (e.g., a mixture of aromatics from a mixture of aliphatics), then distillation can only separate according to boiling points, irrespective of the class of component. In a complex mixture where classes of components need to be separated, this might mean isolating many components unnecessarily. Liquid-liquid extraction can be applied to the separation of classes of components. 

Benzene was first isolated by Faraday in 1825 from the liquid condensed by compressing oil gas. It is the lightest fraction obtained from the distillation of the coal-tar hydrocarbons, but most benzene is now manufactured from suitable petroleum fractions by dehydrogenation (54%) and dealkylation processes. Its principal industrial use is as a starting point for other chemicals, particularly ethylbenzene, cumene, cyclohexane, styrene (45%), phenol (20%), and Nylon (17%) precursors. U.S. production 1979 2-6 B gals. 

If the organic compound which is being steam-distilled is freely soluble in water, an aqueous solution will ultimately collect in the receiver F, and the compound must then be isolated by ether extraction, etc. Alternatively, a water-insoluble compound, if liquid, will form a separate layer in F, or if solid, will probably ciystallise in the aqueous distillate. When steam-distilling a solid product, it is sometimes found that the distilled material crystallises in E, and may tend to choke up the condenser, in such cases, the water should be run out of the condenser for a few minutes until the solid material has melted and been carried by the steam down into the receiver. 

Fig- 23(F) shows a similar distillation assembly for isolating a pure liquid which is present in an organic extract and which may finally require fractional... 

The p-dibromobenzene formed as a by-product in the above reaction usually solidifies when the undistilled residue obtained in the first distillation is chilled. It may then he isolated by adding about lo ml. of methylated spirit and some animal charcoal to the flask, boiling for a few minutes, and filtering hot. On cooling the filtrate in ice-water, crystals of p-dibromobenzene, m.p. 89°, separate recrystallise a second time if necessary to obtain colourless crystals. 

Cool the solution thoroughly in ice-water, and then make it alkaline by the cautious addition (with stirring or shaking) of a solution of 80 g. of sodium hydroxide in ca, 150 ml. of water. Now isolate the free tertiary amine by steam-distillation into hydrochloric acid, etc., precisely as for the primary amine in Stage (D), but preferably using a smaller flask for the final distillation. Collect the 2-dimethylamino- -octane, b.p. 76-78715 mm. Yield, 13-14 g. At atmospheric pressure the amine has b.p. 187-188°. 

When the crude reaction product is made alkaline and steam-distilled, a mixture of quinoline and some unchanged aniline passes over. Pure quinoline can be isolated from this mixture by one of the following methods ... 

The pure quinaldine can now be isolated by either of the following methods, (a) Transfer the acetylated mixture to a Claisen flask (preferably having a short fractionating column below the side-arm) and distil the mixture slowly at water-pump pressure by heating the flask in an oil or silicone bath. The first fraction, of b.p. ca. 50715 mm., contains acetic acid and... 

Steam Distillation. Distillation of a Pair of Immiscible Liquids. Steam distillation is a method for the isolation and purification of substances. It is applicable to liquids which are usually regarded as completely immiscible or to liquids which are miscible to only a very limited extent. In the following discussion it will be assumed that the liquids are completely immiscible. The saturated vapours of such completely immiscible liquids follow Dalton s law of partial pressures (1801), which may be stated when two or more gases or vapoms which do not react chemically with one another are mixed at constant temperature each gas exerts the same pressure as if it alone were present and that... 

Alternatively, the following procedure for isolating the glycol may be used. Dilute the partly cooled mixture with 250 ml. of water, transfer to a distilling flask, and distil from an oil bath until the temperature reaches 95°. Transfer the hot residue to an apparatus for continuous extraction with ether (e.g.. Fig. II, 44, 2). The extraction is a slow process (36-48 hours) as the glycol is not very soluble in ether. (Benzene may also be employed as the extraction solvent.) Distil off the ether and, after removal of the water and alcohol, distil the glycol under reduced pressure from a Claisen flask. 

Allyl Iodide. Use 29 g. (34 ml.) of allyl alcohol and 340 g. (200 ml.) of 57 per cent, hydriodic acid 84 g. of crude iodide are obtained. Upon adding 29 g. (34 ml.) of allyl alcohol to the combined residue in the flask and the aqueous layer and distilling as before, a further 72 g. of crude allyl iodide may be isolated. B.p. 99-101° (mainly 100°). The compound is very sensitive to light the distillation should therefore be conducted in a darkened room and preferably in the presence of a little silver powder. 

An alternative method for isolating the n-butyl ether utilises the fact that n-butyl alcohol is soluble in saturated calcium chloride solution whilst n-butyl ether is slightly soluble. Cool the reaction mixture in ice and transfer to a separatory fimnel. Wash cautiously with 100 ml. of 2-5-3N sodium hydroxide solution the washings should be alkaline to litmus. Then wash with 30 ml. of water, followed by 30 ml. of saturated calcium chloride solution. Dry with 2-3 g. of anhydrous calcium chloride, filter and distil. Collect the di-n-butyl ether at 139-142°. The yield is 20 g. 

From nitriles by treatment with anhydrous Stannous chloride dissolved in ether saturated with hydrogen chloride the resulting crystaUine aldimine stannichloride, [(RCH=NHj)2] SnCl, or (RCH=NH,HCl)2SnCl4, is hydrolysed by warm water, and the aldehyde is isolated by distillation with steam or by extraction with a solvent (Stephen reaction), for example, for R = CH3(CH2)4, i.e., n-amyl ... 

By the action of concentrate aqueous ammonia solution upon esters. This process is spoken of as ammonolysls of the ester, by analogy with hydrolysis applied to a similar reaction with water. If the amide is soluble in water, e.g., acetamide, it may be isolated by distillation, for example ... 

The acid, if monobasic, can usually be distilled directly from the reaction mixture. If this procedure is not possible, the reaction mixture is poured into excess of crushed ice, and the acid is isolated by ether extraction or by other suitable means. The acid is then characterised (Section 111,85). The addition of hydrochloric acid (as sodium chloride say 5 per cent, of the weight of sulphuric acid) increases the rate of the reaction. 

The distillate weighs about 110 g. and contains methyl formate and methylal. If it is placed in a flask provided with a reflux condenser and a solution of 25 g. of sodium hydroxide in 40 ml. of water is added, the methyl formate is liydrolysed to sodium formate and the methylal separates on the surface. The latter may be removed, dried with anhydrous calcium chloride and distilled about 30 g. of methylal, b.p. 37-42°, are obtained. If the aqueous layer is evaporated to diyness, about 25 g. of sodium formate are isolated. 

Maleic acid may be prepared by warming malic acid with acetyl chloride, distilling the mixture under atmospheric pressure to isolate maleic anhydride, and hydrolysing the latter by boding with water. 

Method 1. Arrange the flask containing the reaction mixture for steam distillation as in Fig. II, 40, 1. Proceed with the steam distillation until crystals of p-dibromobenzene appear in the condenser. Change the receiver and continue with the distillation until all the p-dibromobenzeiie has passed over from time to time run out the water from the condenser so that the crystals melt and run down into the receiver. Reject the residue in the flask. Transfer the first distillate to a separatory funnel, wash it with a httle water, and dry the lower layer with a little anhydrous magnesium sulphate or anhydrous calcium chloride filter. Distil slowly from a small distilling flask use a wire gauze or an air bath (Fig. II, 5, 3). Collect the fraction which passes over at 150-170° pour the residue (R), while it is still hot, into a small beaker or porcelain basin for the isolation of p-dibromobenzene. Redistil the fraction of b.p. 150-170° and collect the bromobenzene at 154-157° (3). The yield is 60 g. 

To isolate pure p-dibromobenzene, filter the second portion of the steam distillate through a small Buchner funnel with suction press the crystals as dry as possible. Combine these crystals with the residue (R) and recrystaliise from hot ethyl alcohol (for experimental details, see Section IV,12) with the addition of 1-2 g. of decolourising charcoal use about 4 ml. of alcohol (methylated spirit) for each gram of material. Filter the hot solution through a fluted filter paper, cool in ice, and filter the crystals at the pump. The yield of p-dibromobenzene, m.p. 89°, is about 12 g. 

The benzyl chloride may also be isolated by distillation under atmospheric pressure. The material boiling between 165° and 185° is collected and redistilled the final product is collected at 178-182° (pure benzyl chloride has b.p. 179°). The resulting benzyl chloride is, however, of lower purity unless an efficient fractionating column is used. 

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