Micro distillation

Distillation unit - the Markham semi-micro distillation unit is suitable. Reagents. 

Another design is illustrated in Fig. 2.88 and may be purchased from appropriate suppliers or made to specification the sizes of the pot and of the cold finger are appropriate to the quantity of material to be sublimed, which may be as low as 20 mg. Frequently these assemblies, sometimes with slight modification, may be used for the high vacuum micro-distillation of viscous liquids (Section 2.28). 

Figure 10-11 Schematic picture of the micro-distillation of epichlorohydrin from the dioxane extract of the polymer in vial A into cooled vial B (1) Vial A (2) Vial B (3) PTFE lined septum (4) Sleeve of PTFE tube for isolation (5) Stainless steel tubing, ends are injection needle type sharpened. Int. diameter 1 mm, lenght approx. 20 cm (6) Injection needle for venting (7) 3 ml mark.

More complicated and multi-step reactions are carried out with the aid of other devices commonly used for micro-preparations, micro-distillations, micro-filtrations and others. Special procedures have been developed for a limited number of derivatives, such as esterification on thin layer ( sandwich layer reaction , see p.65) and some others described in Chapter 5 under applications. 

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. 

Micro distillation is sometimes required, e.g. in the chromyl chloride test for a chloride (see Section IV.14). The apparatus depicted in Fig. 11.59 is suitable for the distillation of very small quantities of a mixture. A micro crucible or a micro centrifuge tube may be employed as a receiver. 

Acids of the acetic series are isolated from wine by micro-distillation at 98°C under a stream of nitrogen. Sulphur dioxide is oxidised to sulphuric acid using hydrogen peroxide and eliminated before distillation. Lactic acid is removed by rectification during the distillation, and carbon dioxide does not interfere with the determination. The distillate is mixed with a redox reagent (potassium iodide or bromphenol blue) whose variations in colour intensity are proportional to the level of volatile acidity. 

An alternative to the above method is also largely applied. Dialysis is replaced by a distillation step using a micro distillation column. In the case of total sulphur dioxide, alkaline hydrolysis is replaced by strong acidification and a higher distillation temperature. 

Packed Column GLC Separation of Components. The concentrate from above was first separated into two main fractions by micro-distillation. These were Fraction A, b.p. 25-38°C at 0.1 mm Hg (88J of original concentrate) and Fraction B, b.p.> 38 C at 0.1 mm Hg (residue, 12 S of concentrate). 

The volatile concentrate from the commercial condensate was first separated into 2 main fractions by micro distillation under reduced pressure (0.1mm Hg). The distillation fractions were then resolved into their components by packed column GLC separation first with a 10 m Silicone SF96 packed column with further GLC resolution of the Silicone GLC fractions using a 3 m Carbowax 20-M column. Infrared absorption spectra were measured with the separated components. In some cases HNMR spectra and chemical ionization (C.I.) mass spectra were obtained. This additional... 

C) tert-Butyl Bromide (Sm.). Place in an eight-inch test tube 6 ml of butyl alcohol and 15 ml of 48 per cent hydrobromic acid. Shake at intervals for 5-10 minutes. Separate the upper layer by means of the separatory stopper and wash successively with 5 ml of water and 5 ml of 5 per cent sodium bicarbonate solution. Dry the halide with 1 g calcium chloride, and after 15 minutes distill it from a micro distilling tube. The portion which boils at 72-75° is collected. The yield is about 4 g. 

In the laboratory, discontinuous distillation is performed with glass equipment, e.g. Claisen flasks or micro-distillation kits [34-36]. With a number of mixtures, delay in boiling may cause problems. Overheating may occur, which can cause an explosive discharge. This can be prevented by the addition of boiling stones, which continuously create bubbles as a result of their capillary effect. Another option is the continuous introduction of small amounts of inert gas or agitation of the boiling mixture. 

In-line distillation has rarely been used in flow analysis, but when it has been the basic design of the distillation unit has been maintained. Some advanced micro-distillation units have been proposed, mainly for analytical procedures with electrochemical detection [309—311]. A current tendency is to place several units in the manifold for successively performing different in-line analyte separation (and/or concentration) steps, e.g., distillation, dialysis and filtration. It is also possible to perform a variant of in-line distillation under constant temperature. This approach has been called isothermal distillation, membraneless gas diffusion or thin layer distillation, and discussed in 8.5.3.2. 

S. McLeod, Micro-distillation unit for use in continuous flow analyzers. Its construction and use in determination of ammonia and nitrate in soils, Anal. Chim. Acta 256 (1992) 107. 

Mansfeldt, T. Biernath, H. (2000) Determination of total cyanide in soils by micro-distillation. Anal. Chim. Acta., 406, 283-288. 

Babcock s micro-distillation apparatvts for use at reduced pressures... 

In contrast to an empty column (chap. 7.3.1), the Vigreux column has a considerable surface area and leads the reflux to the centre by means of the indentations in the walls. Shrader and Ritzer [5] equipped their micro-distillation apparatus with such a column (Fig. 129). Other special features of this equipment are the flat-bottomed flask a, which ensures a constant surface area for evaporation, and the receiver h containing tubes c of 0.1 ml capacity. The distillate is led to the tube in question by the glass thread d. The apparatus can, however, be employed only for high-boiling... 

Micro-distillation apparatus of Krell for atmospheric and reduced pressures charge 1 — 10 ml... 

Both packed and plate columns can only partly beusedforsemi-micro-distillation.s since their hold-ups are too large (see chap. 4.10.5). The point is to keep the column dimensions as small as possible for a given amount of material. Only helices of 1.6 to 2 mm size can then be used as packing (chap. 7.3.2, 7.3.3 and 7.8). Concentric tube (chap. 7.3.1) and spinning band columns (chap. 7.3.5), however, are particularly suitable for sharp separations of very small amounts. Both types are also of great... 

Micro-distillation apparatus of Shrader and Bitzer with Vigreiix column... 

Klenk s apparatus for micro-distillation, with spiral column, for charges of 4 ml or more... 

The heating of small flasks presents difficulties in micro-distillations, and flooding of the column often occurs. If possible the diameter of the latter should therefore be not less than 6—8 mm. A micro-heating device, equipped with a dark infra-red lanq),... 

Favourable features of empty columns are that they give a low hold-up and a small pressure drop, so that their main applications are in the fields of micro-distillation (section 5.1.1), high-temperature distillation (5.3.2) and vacuum distillation (5.4.1). In such columns the exchange takes place between the vapour and the film of liquid falling down the walls. The possibilities and problems involved in the use of falling films have been studies in detail by Malewski [15]. 

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