Sublimation pressure

The purification of solids by low pressure sublimation is described in Section 11,45. 

The common methods of purification, discussed below, comprise distillation (including fractional distillation, distillation under reduced pressure, sublimation and steam distillation), crystallisation, extraction, chromatographic and other methods. In some cases, volatile and other impurities can be removed simply by heating. Impurities can also sometimes be eliminated by tbe formation of derivatives from which the purified material is regenerated (see Chapter 2). 

Quinazoline [253-82-7] M 130.2, m 48.0-48.5 , b 120-121 /17-18mm, pK, -4.51 (aq H2SO4, anhydrous dication), pK 2.01 (anhydrous monocation), pK3 4.3 (equilibrium with 3,4-hydrated species), PK4 12.1 (hydrated anion). Purified by passage through an activated alumina column in benzene or pet ether (b 40-60°). Distd under reduced pressure, sublimed under vacuum and crystd from pet ether. [Armarego 7 Chem 1170 1961.]... 

White powder, hexagonal graphite-like form or cubic crystal cubic form similar to diamond in its crystal structure, and reverts to graphite form when heated above 1,700°C density 2.18 g/cm melts at 2,975°C (under nitrogen pressure) sublimes at 2,500°C at atmospheric pressure insoluble in water and acid attacked by hot alkalies and fused alkali carbonates not wetted by most molten metals or glasses. 

White to pale yellow, fuming, deliquescent, crystalline masses with pungent, unpleasant odor mp, 148°C under pressure. Sublimes at about 100°C without melting bp, 160°C. ... 

Each pure hydrocarbon has a pressure-temperature diagram similar to the one shown in Figure 18. To be sure, the actual vapor pressures, sublimation pressures, critical values, etc., are different for each substance, but the general characteristics are similar. If such a diagram is available for a given substance, it is obvious that it could be used to predict the behavior of the substance as the temperature and pressure are varied. For example, in the diagram shown... 

The 15-mL centrifuge tube and adapter are placed in the flask so that the tip of the centrifuge tube is about 3 to 8 mm above the bottom of the flask (Fig. 13). The flask is clamped with a three-prong clamp. Many substances sublime at atmospheric pressure (see following experiment). For vacuum sublimation, the sidearm of the flask leads to an aspirator or vacuum pump for reduced pressure sublimation. The vacuum source is turned on and the centrifuge tube filled with ice and water. The ice is not added before applying the vacuum so atmospheric moisture will not condense on the tube. 

Fluoroammonium perchlorate has an appreciable vapour pressure, subliming... 

Some solids, such as iodine and carbon dioxide, vaporize at atmospheric pressure without passing through the liquid state. This process is known as sublimation. Solids exhibit vapor pressures just as liquids do, but they generally have much lower vapor pressures. Solids with high vapor pressures sublime easily. The characteristic odor of a common household solid, j) r -dichlorobenzene (moth repellent), is due to sublimation. The reverse process, by which a vapor solidifies without passing through the liquid phase, is called deposition. 

Colorless gas. Odor of garlic. Very irritating to mucous membranes. Thermally siable up to about 1000 . d° (liq) 2,162 d (solid —195 ) 3,148. mp —15 (under 3032 mm pressure). Sublimes at —36.5. On contact will) water, hydrolyzes to GeO and H2GeFt. Does not attack glass when absolutely dry. Corrodes mercury, grease. 

White to pale yellow, fuming, deliqnesc, cryst mass pun -gent, unpleasant odor attacks the eyes and mucous membranes. mp 148 under pressure sublimes at about 100° without melting, bp 160°. Hydrolyzed by water to form phosphoric acid and hydrogen chloride. Reacts with alcohols (ROH) to form the corresponding chloride (RC1). Sol in carbon disulfide or tetrachloride. Keep in tightly closed containers and handle with caution. Corrosive. 

Between difFerent aluminum halides, AICI3 has the lowest temperature of transition to the gas phase (atmospheric-pressure sublimation at 453 K), which simplifies the plasma-chemical process ... 

White to yellow crystalline solid deliquescent pungent odor mp 148°C (298°F) under pressure sublimes at 100°C (212°F) bp 160°C (320°F) soluble in carbon tetrachloride and carbon disulfide reacts with water and alcohol. 

Diphenyl carbonate (phenyl carbonate) [102-09-0] M 214.2, m 80 , 168 /15mnt, 306 /760inm. Purify it by distillation under reduced pressure, sublimation, or by gas chromatography with 20% Apiezon on Embacel, and... 

Many organic compounds sublime readily under reduced pressure. When the vapor pressure of the solid equals the applied pressure, sublimation occurs, and the behavior is identical to that shown in Figure 17.1B. The solid phase passes directly into the vapor phase. From the data given in Table 17.1, you should expect camphor, naphthalene, and benzoic acid to sublime at or below the respective applied pressures of 370,7, and 6 mm Hg. In principle, you can sublime p-nitrobenzaldehyde (last entry in the table), but it would not be practical because of the low applied pressure required. 

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