Sublimation water trap

If you re going to pull a vacuum in the sublimator, do it now. If the vacuum source is a water aspirator, put a water trap between the aspirator and the sublimator. Otherwise you may get depressed if, during a sudden pressure drop, water backs up and fills your sublimator. Also, start the vacuum slowly. If not, air, entrained in your solid, comes rushing out and blows the crude product all over the sublimator, like popcorn. 

A photograph of a commercial laboratory apparatus is shown in Figure 8-2, p. 86. (A) is the sample holder. (B) is a special holder so that a sample can be added or removed without breaking the vacuum on the other sample chambers. (C) is a large trap to collect the sublimed water, (D) is a McLeod gauge to measure the pressure, and (E) is the temperature gauge. The pump (F) may be a simple mechanical pump, but is more likely a mechanical-diffusion pump combination. 

In solvent processing a condenser and water trap must be provided. The condenser must be designed to prevent blocking by sublimed phthalic anhydride. 

Why apply the vacuum to the sublimation system before you turn on the cooling water to the water condenser 5-50. Why place a water trap in the vacuum line when using an aspirator to obtain the vacuum ... 

Niobium Penta.fIuoride, Niobium pentafluoride is prepared best by direct fluorination of the metal with either fluorine or anhydrous hydrofluoric acid at 250—300°C. The volatile NbF is condensed in a pyrex or quartz cold trap, from which it can be vacuum-sublimed at 120°C to yield colorless monoclinic crystals. It is very hygroscopic and reacts vigorously with water to give a clear solution of hydrofluoric acid and H2NbOF ... 

If the pump is a filter pump off a high-pressure water supply, its performance will be limited by the temperature of the water because the vapour pressure of water at 10°, 15°, 20° and 25° is 9.2, 12.8, 17.5 and 23.8 mm Hg respectively. The pressure can be measured with an ordinary manometer. For vacuums in the range lO" mm Hg to 10 mm Hg, rotary mechanical pumps (oil pumps) are used and the pressure can be measured with a Vacustat McLeod type gauge. If still higher vacuums are required, for example for high vacuum sublimations, a mercury diffusion pump is suitable. Such a pump can provide a vacuum up to 10" mm Hg. For better efficiencies, the pump can be backed up by a mechanical pump. In all cases, the mercury pump is connected to the distillation apparatus through several traps to remove mercury vapours. These traps may operate by chemical action, for example the use of sodium hydroxide pellets to react with acids, or by condensation, in which case empty tubes cooled in solid carbon dioxide-ethanol or liquid nitrogen (contained in wide-mouthed Dewar flasks) are used. 

The kinetics of many decompositions are conveniently studied from measurements of the pressure of the gas evolved in a previously evacuated and sealed constant volume system. It is usually assumed, and occasionally confirmed, that gas release is directly proportional to a, so that the method is most suitable for reactants which yield a single volatile product by the irreversible breakdown of a substance that does not sublime on heating in vacuum. A cold trap is normally maintained between the heated reactant and the gauge to condense non-volatile products (e.g. water vapour) and impurities. The method has found wide application, notably in studies of the decomposition of azides, permanganates, etc., and has been successfully developed as an undergraduate experiment [114—116]. 

Better yields are obtained at low pressures (preferably below 5 mm.) because of more efficient sublimation of coumalic acid. The submitters report that a water aspirator could be used with crude (unrecrystallized) coumalic acid to avoid damage to the vacuum pump by untrapped corrosive vapors, and that yields of a-pyrone averaged 45% in this modification. The checkers used a mechanical pump with an efficient sodium hydroxide trap in all runs. 

However, in some reactions a very high grade of anhydrous aluminium chloride may be required. This is conveniently prepared by placing the crushed pellets in a suitably sized round-bottomed flask fitted with a simple distillation bend to which is attached a two-necked round-bottomed receiver flask the second outlet is connected to a water pump via a drying tower similar to that shown in Fig. 4.2 and filled with granular calcium chloride. The distillation flask is heated cautiously with a brush flame and the aluminium chloride sublimes under reduced pressure. It is inadvisable to use an oil immersion rotary pump because of possible corrosion damage even with suitably placed protection traps. 

Fie. 40. Vacuum distillation equipment for substances which solidify easily (napnthols, phenylenediamine, etc.). The apparatus for large quantities (1000-30(X) kg.) is equipped with a stirring mechanism to prevent charrine. 1, distillation vessel 2, receiver with steam or water jacket 3, steam heated times to prevent solidification 4, trap to collect water and sublimate 5, line to pump. 

After the filtration is finished, the apparatus is filled with dry nitrogen, and the receiver flask is removed and capped. It is attached to the subhmer shown in Fig. 2. The system is evacuated, and the ether is condensed from the reaction mixture into an empty flask on the manifold with liquid nitrogen. When a solid residue remains in the flask, a —20° cold bath is placed around the trap of the sublimer. The manifold is opened to the pump. After 10 minutes of pumping, a water bath at 40 to 50° is put around the flask. If the sublimate begins to collect in the neck of the flask or or in the curved part of the sublimer, a stream of warm air is blown over these areas with a hair dryer. After the sublimation is complete, t the apparatus is removed from the manifold and taken into the dry-box. The product is obtained in 85 to 95% yield (5.2 to 6.0 g.) (The checkers report 66 %.)... 

After the preparation of the nitrogen(V) oxide is complete, 18.2 g. (0.10 mol) of anhydrous vanadium(V) oxide is placed in the two-necked 300-ml. reaction vessel E. The flask is heated to 100° while the vacuum is maintained, in order to dry the metallic oxide before introducing the anhydrous nitrogen (V) oxide. When the 100° temperature is reached, the vacuum in E is released at stopcock b. The flask E is allowed to cool to room temperature and is then immersed in a Dry Ice-methanol bath. Stopcock 6 is changed to allow flow of the nitrogen(V) oxide into the reaction vessel E. Stopcocks e and / are opened to the outside and stopcocks c and d (to the vacuum pump) are closed. The Dry Ice-methanol baths are removed from traps A, C, and D, and under a flow rate of 0.06 standard cubic feet per minute (1.7 l./minute) of ozone the nitrogen (V) oxide is sublimed into the reaction vessel. To assure complete sublimation of the nitrogen(V) oxide, traps A, C, and D may be immersed in a water bath at 50°. 

Freeze drying, also known as lyophilization, is a process in which water is sublimated from the product after freezing. This process can be used in many different ways to achieve the same end point. In one of the freeze-drying formulation methods, drug is physically trapped in a water-soluble matrix (water-soluble mixture of saccharide and polymer, formulated to provide rapid dispersion, and physical strength), which is freeze dried to produce a product that dissolves rapidly when placed in the mouth. The ideal candidate for this kind of manufacturing method would be a molecule that is chemically stable and water insoluble, with a particle size lower than 50 In another method, lyophili-... 

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