Vacuum-line techniques

These reactions require vacuum line techniques. Vacuum lines incorporating greaseless stopcocks are preferred over those greased with Kel-F or Apiezon N silicone grease reacts rapidly and must be avoided. 

The synthetically useful dianions [M3(CO)u] were first isolated by Shore and co-workers as the Ca (M = Ru) and the K" " (M=Os) salts by the reduction of M3(CO)i2 using alkali metal benzophenone solutions in THF. [Ru3(CO)xi] reacts with Ru3(CO)i2 to form the higher nuclearity clusters [Ru4(CO)i3] and [Ru6(CO)i8] but the triruthenium anion can be obtained in high purity by slowly adding triruthenium dodecacarbonyl to an excess of reducing solution using vacuum-line techniques. Vacuum-line syntheses of both dianions have been described in detail. ... 

The first definitive studies of boron hydrides were carried out by Alfred Stock in Germany starting about 1912 (1). Through extensive and now classic synthetic studies, the field of boron hydride chemistry was founded with the isolation of a series of highly reactive, air-sensitive, and volatile compounds of general composition and This accomplishment required the development of basic vacuum line techniques for the... 

Not only the preparation of so far unknown compounds, but also the development of new synthesis techniques such as the Schlenk technique and vacuum-line technique which allow the handling and manipulation of air- and moisture-sensitive, pyrophoric compounds, are the most striking breakthroughs of their fascinating work. 

Some of the procedures described in the following chapters had to be carried out under an inert atmosphere, nitrogen or argon, to minimize contact with oxygen and moisture. It is then necessary to use Schlenk techniques including the utilization of a vacuum line connected to a high vacuum pump and an inert gas inlet. The use of such equipment requires experience in working under anhydrous conditions. 

The test (b) we carried out typically as follows but we have also used many variations of this procedure [18]. We used an assembly of connected reaction tubes attached to the vacuum line. In one tube we polymerised (I) by perchloric acid in methylene dichloride. Reaction was stopped by adding sodium phenate, and any phenol formed from secondary oxonium ions was neutralised with sodium hydride. The volatile compounds were distilled into a second tube where the same experiment was repeated. This technique is based on that of Saegusa and Matsumoto [19] phenol and phenyl ethers can be estimated separately by their UV spectra. 

How gases are transferred, distilled, or otherwise processed in vacuum lines is briefly discussed under the different elements. A more detailed description can be found in the recently published Handbook of Stable Isotope Analytical Techniques, edited by de Groot (2004). 

The syntheses of disilathiane and its methylated analogues by the reaction of mercuric sulfide with gaseous iodosilanes is described here in detail. The procedures are convenient, take about 2 hours, and are well suited to small-scale vacuum-line techniques, using a minimum of special appartus. The yields are in the range of 90-95%. 

The secret of successful h.v.t. is careful planning, and the choice of the appropriate apparatus and technique will become easier with practice. The best-planned vacuum line will be usable for operations for which it was not designed originally, which means that it is versatile and adaptable. It should be suitable for preparative, kinetic and analytical work, and it should not be so complicated that cleaning requires extensive dismantling and reconstruction. The next three chapters will provide the reader with the information necessary to design the right system for his particular purposes. 

The freeze valve Another simple valve which is extremely effective and especially useful when one needs to seal off a unit containing a volatile liquid from the vacuum line, is the freeze-valve. This is a glass U-tube of not more than 5 mm i.d. in the duct connecting the two parts which need to be separated. If some of the liquid is frozen into the U so that the tube is blocked, the low pressure side of the U can be sealed off without the necessity of freezing the bulk of the liquid on the other side. This technique can be especially useful when the flask containing the bulk liquid is very large or if... 

The sample preparation vacuum line (often called spray-on line ) should allow for (a) controlled mixing of the host gas with the substrate (or with other components that are added to the matrix) by manometric techniques and (b) the controlled release of the gas (mixture) toward the inlet system of the cryostat. These conditions are met by a vacuum line that incoporates a storage bulb for the gas (mixture), inlets for attachment of evacuable containers that allow degassing of the substrate prior to its mixing with the host gas, pressirre gauges that cover suitable ranges, a needle valve that allows the controlled release of the gas, possibly via a flowmeter, and interfaces to the bottles that contain the host gas(es), and to the inlet system that is attached to the vacuum shroud of the cryostat. 

An alternative, and more expensive, technique involves the application of commercial glass inserts, which are offered by Wilmad for all commercial MAS NMR rotor types. Approximately 60 or 200 mg of catalyst powder can be filled into a 4-mm or 7-mm glass insert, respectively. After calcination of the catalyst and adsorption of reactant molecules introduced from a vacuum line, the glass insert is sealed at the waist (Fig. 7). To prevent heating of the sample, the glass ampoule is clamped in one of the chucks and cooled by liquid nitrogen. 

For example, 100 ml of air at 25 °C and at 100% humidity contains about 2.5 mg of water. Therefore, when we handle electrolyte solutions in non-aqueous solvents, we must estimate the amount of water introduced from the air and the extent of its effect on the measurements. The vacuum line techniques and the glove box operations for electrochemical studies in non-aqueous solvents have been dealt with in several books. See, for example, Kissinger, P.T., Heineman, W. R. (Eds) Laboratory Techniques in Electroanalytical Chemistry, 2nd edn, Marcel Dekker, New York, 1996, Chapters 18 and 19. 

Vacuum-lines, Schlenk and Glovebox Techniques. Manipulations involving materials sensitive to air or water vapour can be carried out by these procedures. Vacuum-line methods make use of quantitative transfers, and P(pressure)-V(volume)-T(temperature) measurements, of gases, and trap-to-trap separations of volatile substances. 

All manipulations are carried out using inert atmosphere techniques.8 The vacuum line used in the following preparation is similar to that shown in Figure 2. 

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