High vacuum sublimation

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. 

High vacuum sublimation of the 3-monobenzoate of (32) or tosylchloride dehydration gives 3/ -benzoyloxy-7-methylenecholest-5-ene (33). The configuration of (32) is probably as shown since 7a-hydroxy steroids dehydrate readily to yield homoannular dienes. In an analogous reaction ethyl and iso-butyl Grignard reagents give alkylidene compounds as the only isolated products. 

A mixture of pyrimidine-4,5-diaminc (5.5 g, 50 mmol), ethyl acetoacetate (9.75 g, 75 mmol) and xylene (400 mL) was refluxed for 5h with stirring, cooled and refrigerated overnight. The resulting solid was collected and washed with xylene yield 6.70 g (76 %). High-vacuum sublimation gave an analytical sample, mp 250-252 C (dec.). 

A sample of PeRu (614 mg, 1 mmol) was suspended in molten 4,4 -bipyridine (4.7 g, 30 mmol) and the mixture was heated for 24 h at 120 "C. Excess ligand was removed either by washing of the mixture with EtOH or by high-vacuum sublimation at 90 C. A violet powder was obtained yield 926 mg ( 100%). 

Overheating dining high-vacuum sublimation may produce pyrophoric manganese which explodes on opening the sublimer to atmosphere. 

If lead nitrate is used rather than the chloride or acetate as the source of divalent lead, the crude dicyclopentadienyllead may explode violently during purification by high-vacuum sublimation at 100-130°C. 

In Figure 1, a general scheme used in our group for the careful isolation of food volatiles is shown. Usually, the food is extracted with diethyl ether at room temperature and, after concentration of the extract, the volatiles are separated from the non-volatile material by high vacuum sublimation [10, 11], In case of fat-rich products (e.g., butter, sesame seeds or soybean oil) a modified version of the high vacuum sublimation apparatus is used [12]. 

Cyclopentadienylsodium. Use of lead nitrate to prepare cyclopentadienyllead may result in explosion during purification of the crude product by high-vacuum sublimation at 108— 130°C.10... 

Nitrosyl derivatives of the homologues of chromium may be made directly as insoluble precipitates by decomposing the complex anions [CbH5Mo(CO)3] and [CsHsW (CO) 3] with nitric oxide in aqueous media 85). After high-vacuum sublimation at 55-60° the orange-red... 

Figure 6-15. The kinetic phase diagram of high-vacuum-sublimed films as a function of deposition T and nominal substrate thickness h.

ODA was purified by high vacuum sublimation followed by zone refining through 50 zones. 

The reaction of K[C(CN)3] 73 with one equivalent of [SNS][AsF6] 17a led to the neutral compound (NC)2C=CNSNS 74, which can be crystallized as black prisms by high-vacuum sublimation (85°C, 10 7 r) [92JCS(D)859]. Although it is esr-inactive, its dark lustrous appearance makes it somewhat anomalous for this group of materials. 

Figure 16 High-vacuum sublimation apparatus for recovery of volatile solid ligands RBF diameter 100 mm.

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