Distillation of small quantities

The steam distillation of small quantities of material may be conducted in the apparatus of Fig. 11, 41, 5. The substance to be distilled is placed in the small inner tube (a specially constructed test-tube) and water is boiled in the outer bolt-head flask. The volume of the liquid in the inner tube does not increase appreciably since it is immersed in the hot liquid in the flask. 

The boiling point is one of the most important physical constants of a liquid. It is also easily determined with sufficient accuracy for most purposes if a reasonable quantity of a pure substance is available, for then it is only necessar to carefully distill the sample, noting both the vapor temperature and the barometric pressure. A particularly convenient apparatus for distillation of small quantities is shown in Fig. 1-10. The shape of the flask here is a desirable one because it confines the liquid to a smaller area than does a round-bottom flask. Thermometers with standard taper joints (1-in. immersion) are very convenient and reduce the possibility of contamination, and in vacuum distillation, of leakage. They are also calibrated for partial immersion, thus making emergent stem corrections (page 83) unnecessary. They... 

The Hempel Still-head.—The great advantages of the Hempel apparatus(5) are simplicity and efficiency on the other hand the amount of liquid in the still-head is excessive, and it is therefore unsuitable for the distillation of small quantities of liquid. 

Acetamide is thus obtained as a colourless crystalline solid, which has a characteristic odour of mice, stated to be due to the presence of small quantities of methylacetamide, CH3CONHCH3. The acetamide can be purified and rendered odourless by re-crystallisation from acetone, and then has m.p. 82°, b.p. 223°. If this recrystallisation is contemplated, the distilled material should be collected directly into a small weighed beaker or conical flask, so that the solidified acetamide can be readily broken up and removed. 

Assemble in a fume-cupboard the apparatus shown in Fig. 67(A). Place 15 g. of 3,5-dinitrobenzoic acid and 17 g. of phosphorus pentachloride in the flask C, and heat the mixture in an oil-bath for hours. Then reverse the condenser as shown in Fig. 67(B), but replace the calcium chloride tube by a tube leading to a water-pump, the neck of the reaction-flask C being closed with a rubber stopper. Now distil off the phosphorus oxychloride under reduced pressure by heating the flask C in an oil-bath initially at 25-30, increasing this temperature ultimately to 110°. Then cool the flask, when the crude 3,5-dinitro-benzoyl chloride will solidify to a brown crystalline mass. Yield, 16 g., i.e,y almost theoretical. Recrystallise from caibon tetrachloride. The chloride is obtained as colourless crystals, m.p. 66-68°, Yield, 13 g Further recrystallisation of small quantities can be performed using petrol (b.p. 40-60°). The chloride is stable almost indefinitely if kept in a calcium chloride desiccator. 

Steam distillation.—For small quantities of compounds, which are readily volatile in steam, water may be added to the contents of the reaction flask (e.g. Figs. XII, 2,4 and XII, 2, 11) and the flask heated in an air bath or with a small flame. Alternatively, if preferred, steam may be passed into the reaction flask from a separate generator this may consist of a small conical flask provided with the usual safety tube (compare Fig. II, 40, 1). 

Vanadium (III) acetonylacetonate [13476-99-8] M 348.3, m 181-184°, 185-190°, pKj 2.92, pK 3.5(for aquo V hydrolysis). Crystd from acetylacetone as brown plates. It can be distilled in small quantities without decomposition. It is soluble in CHCI3 and CgHg and evaporation of a CHCI3 solution yields brown crystals which are washed with cold EtOH and dried in vacuum or at 100° in a CO2 atmosphere. Under moist conditions it readily oxidises [V(AcAc)3 lo V(AcAc)20]. [J Chem Soc 103 78 1913, Inorg Synth 5 105 1957 Anal Chem 30 526 I958 UV J Am Chem Soc 80 5686 1958.]... 

Distill a small quantity each day to obtain relatively pure o-xylene from a mixture of ortho and para xylene, having boiling points of 142.7°C and 138.4°C, respectively. The feed is 15 Ib-mols (about 225 gallons) per batch, at 0.20 mol fraction para. The desired residue product is 0.020 in the kettle, while the distillate is to be 0.400 mol fraction para. A distillation column equivalent to 50 theoretical plate is to be used. 

The actual isolation of zinc metal on an appreciable scale seems to have occurred first in China in the 10th Century AD (Xu, 1990), using an upwards distillation procedure from secondary (oxidized) zinc minerals. Earlier finds of metallic zinc (such as that at the Agora, noted above) are possibly explained by the chance condensation of small quantities of zinc in the furnace during the production of lead and silver from mixed ores. Much attention has been focused in recent years on northern India, particularly the Zawar region,... 

Smirnova et al. [5] have described a simple non-enzymatic method of quantitative determination of adenosine triphosphate in activated sludge from aeration tanks. Extraction of the nucleotides in boiling distilled water was followed by removal of the protein impurities by acidification. Barium salts of di- and triphosphates of the nucleotides were precipitated and the precipitate was washed and dissolved in acid to convert the barium salts to sodium salts. The quantity of adenosine triphosphate was determined quantitatively by inorganic phosphorus in the liquid over the precipitate before and after acid hydrolysis, and by ultraviolet absorption spectra. The method was tested in activated sludge from operational sewage works. There was good agreement between the adenosine triphosphate content determined spectrophotometrically and by phosphorus, despite the presence of small quantities of secondary impurities. 

In the arrangement discussed, the feed is introduced continuously to the column and two product streams are obtained, one at the top much richer than the feed in the MVC and the second from the base of the column weaker in the MVC. For the separation of small quantities of mixtures, a batch still may be used. Here the column rises directly from a large drum which acts as the still and reboiler and holds the charge of feed. The trays in the column form a rectifying column and distillation is continued until it is no longer possible to obtain the desired product quality from the column. The concentration of the MVC steadily falls in the liquid remaining in the still so that enrichment to the desired level of the MVC is not possible. This problem is discussed in more detail in Section 11.6. 

Vanadium (III) acetonylacetonate [13476-99-8] M 348.3, m 181-184°, 185-190°. Crystd from acetylacetone as brown plates. It can be distilled in small quantities without decomposition. It is soluble in CHCI3 and CgHg and evaporation of a CHCI3 solution yields brown crystals which are washed with cold EtOH... 

Stirring is continued for one hour after all the diazo solution has been added. The mixture is now filtered and the filtrate concentrated to a volume of approximately 51. this is deep brown in color. Concentrated hydrochloric acid is added in small portions, and the tarry material which separates is filtered off. The add is added until after filtering a clear, pale yellow solution results. The phenylarsonic add is now precipitated by the addition of more hydrochloric acid. An excess must be avoided since it causes a certain amount of the phenylarsonic acid to go into solution. When this neutralized mixture has cooled, the product is filtered off and washed with a little distilled water. Small quantities of phenylarsonic acid remaining in the filtrate may be predpitated as the ferric salt by adding ferric chloride. The yield of white or cream-colored product averages more than 800 g. (50%) and in many cases runs well over 1000 g. (62%). After recrystallization from water the product is practically white and softens at 158°, passing into the infusible anhydride, C6H5ASO2. 

Batch distillation (Fig. 16) is often preferable to continuous distillation when small quantities of feed material are processed. A liquid feed is charged to a still pot and heated until vaporization occurs. Vapor leaves the top of the column, and after condensation, part is removed as product and the rest returned to the column as reflux. As distillation proceeds, the contents of the still pot and the overhead product become richer in less volatile components. When operated at a fixed reflux ratio, an overhead product cut is collected until the product composition becomes unaccceptable. As an alternative, the reflux ratio can be gradually increased to hold the product composition constant as the cut is taken. For a fixed rate of heat addition to the still pot, the latter option results in a steadily declining product flow rate. After the first cut, subsequent... 

Another popular method for distilling small quantities is to use a Buchi Kugelrohr apparatus (Fig. 11.14). The key features of this system are (i) a horizontal glass oven with an iris closure, which heats the flasks efficiently (ii) short-path distillation between a series of bulbs which can be moved horizontally in and out of the oven (iii) a motor to rotate the bulbs. The Kugelrohr can be used to distil very small quantities (< lOOmg) and can be operated at high vacuum. A simple distillation is carried out as follows ... 

Distillation is used to separate the components of a liquid mixture by vaporizing the liquids, condensing the vapours and collecting the liquid condensate. Separation is the result of the differing boiling points of the individual constituents of the mixture and the efficiency of the distillation column. You may be required to purify a hquid by distillation, which involves the removal of small quantities of impurities, or to separate a mixture of liquids by fractional distillation, each of which can then be purified by distillation. 

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. 

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