Distillation, apparatus purification

The solution is concentrated under reduced pressure. The remaining oil is distilled under reduced pressure using a simple distillation apparatus. After a small forerun, 27 g (0.179 mol, 26iS yield) (Note 5) of 1 is collected, as a light yellow oil, bp 90-94 C/O.05 mn (Note 6). Further purification is accomplished by a second distillation under reduced pressure, bp 90.2 C/0.05 mm (Notes 7 and 8). 

The efficiency of a distillation apparatus used for purification of liquids depends on the difference in boiling points of the pure material and its impurities. For example, if two components of an ideal mixture have vapour pressures in the ratio 2 1, it would be necessary to have a still with an efficiency of at least seven plates (giving an enrichment of 2 = 128) if the concentration of the higher-boiling component in the distillate was to be reduced to less than 1% of its initial value. For a vapour pressure ratio of 5 1, three plates would achieve as much separation. 

The aldehyde is separated from the lower aqueous layer as a colorless liquid and dried over 10 g. of anhydrous sodium sulfate. The drying agent is removed by filtration, and the product is distilled under reduced pressure using a Claisen distillation apparatus to give 92-94 g. (82-84%) of cyclohexanecarboxaldehyde, b.p. 52-63° (18 mm.), 1.4484 (Notes 10, 11). A purity of about 98% was established by gas chromatographic analysis (Note 12) the product is suitable for synthetic use without further purification (Note 13). 

Nitroethylene, IT2C — CHNCH, is a sensitive compound that must be prepared with great care. Attempted purification of nitroethylene by distillation often results in low recovery of product and a white coating on the inner walls of the distillation apparatus. Explain. 

For complete purification from chlorine, distil the silicon tetrachloride over copper shavings in an apparatus for distillation under atmospheric pressure (see Fig. 20) and collect the fraction boiling at 57-59 °C. First thoroughly dry the distillation apparatus with... 

A short-path distillation procedure may be used in situations where a simple distillation is required, as purification from non-volatile components/fractional distillation with a Kugelrohr apparatus is difficult. A water-jacketed, semi-micro distillation apparatus is illustrated in Figure 1.7. Heating can either be achieved with the aid of an oil-bath, an isomantle, or a flame (Caution ensure that there are no flammable solvents nearby). For larger scale distillations, a round-bottomed flask should be attached to a distillation column, a still-head, and condenser. The column used in the distillation is variable, and may be either a Vigreux column or a column packed with glass helices. 

For liquids with a high boiling point, or which decompose on heating, distillation under reduced pressure is the usual method of purification. Again it is convenient and effective to use a one-piece distillation apparatus in conjunction with a double manifold for this type of distillation. The procedure is described in more detail in Chapter 11, and some examples of reagents which can be distilled under reduced pressure are given in Table 6.2. 

The process conducted in batch-type counter-flow apparatus (Figure 30.17) equipped with capillary PP Acccurel membranes showed good effectiveness of membrane distillation for purification of radioactive waste. Permeate obtained was pure water. All solutes together with radioactive compounds were rejected by the hydrophobic membrane. At tenfold volume reduction of the initial portion of waste, approximately tenfold concentration of radioactivity in the retentate stream was reached, while radioactivity of permeate retained on the level of namral background (Figure 30.18). As was observed in experiments small sorption in the system took place. However, permeate was free of radioactive substances and other dissolved compounds, the concentration and radioactivity factors sometimes slightly differed from volume reduction factors. 

The most difficult part of a semimicro preparation is the purification of the product. If the product is a solid, it may usually be purified by recrystallization or chromatography as described previously (pages 99 and 156). The amount of solvent should be kept to a minimum in recrystallization, so that a large portion of the material will not be lost in the mother liquors. If the product is a liquid, it is rarely possible to effect a good purification by distillation, and with quantities less than 500 mg, the holdup of most distillation apparatus becomes prohibitive. The most satisfactory method for the purification of small quantities of liquids is vapor-phase chromatography (page 165). This method is ideally suited for handling 10 to 500 mg of material and will provide a separation which can be matched by few other methods, with essentially no loss due to holdup. 

The Arabs were the perfecters if not the inventors of the art of distillation, in which a liquid is converted into a vapor by boiling, and then condensed back into a liquid by cooling. The aim of distillation is purification. The alchemists developed different vessels for the distillation process. The lower part of a still, the apparatus used for distillation, is called a cucurbit the liquid is heated in this container. The upper part, where the heated vapor condenses again, is the alembic. The receiver for the distilled liquid is the aludel... 

To a soluiion of l-bromo-2-vinylcyclopropane (40 mmol, 7 3 mixture of cis and traits) in 80 mL of Et20 arc added at —78 C 48 mmol of r-BuLi (1.5 M in pentane) over 5 min. The resulting solution is stirred for 1.5 h at -78 C and subsequently warmed to 0 ,C. A solution of alkoxyenone 55b (20 mmol) in 10 mL of F.t20 is then added over a period of 2 min. The reaction mixture is stirred for 15 min at 0 C and 15 min at r.t., and then carefully poured into a separatory funnel containing 100 mL of 2 N HC1. Intermittent agitation of the above mixture (15 min) followed by standard workup provides divinylcyclopropanes 56b yield 91% (90% purity, 7 3 mixture of cis and irons), which is purified by silica gel chromatography (EtjO/hexane 3 7). Compound 56b (2 M benzene solution) upon thermolysis (170-180 C, 2 h) in a sealed Pyrex tube provides ketone 57b after purification yield 87% bp 54- 59 CO. I5 Torr. Alternatively, ketone 57b can be prepared by heating (250 C, 5 min) the crude mixture of compound 56b in a distillation apparatus followed directly by distillation of ketone 57b yield 72%. 

After heatingwithcopper, theTiCUiscooledand suction-filtered through a very dry filter funnel, and the filtrate is transferred for further purification (removal of SiCU and dissolved nonvolatile hydrates) to the distillation apparatus described below (Fig. 295). 

Purpose. In this exercise you will become familiar with a powerful modification of the classic Hickman still the Hickman-Hinkle spinning band distillation apparatus. This small still is one of the most efficient techniques developed for the purification of small quantities of liquids. You will develop the skills for handling small quantities of liquids and their purification by distillation, and become familiar with these techniques, so that... 

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