Sublimation under vacuum

Halides. Xenon duorides, xenon oxide tetraduoride [13774-85-1XeOE, and their complexes are the only thermodynamically stable xenon compounds. Xenon diduo ride [13709-36-9] xenon tetraduoride [13709-61-0], and xenon hexaduoride [13693-09-9] are colodess, crystalline soHds which can be sublimed under vacuum at 25°C. The mean thermochemical bond energies are XeE2, 132.3 0.7 kJ/mol (31.6 0.2 kcal/mol) XeE ... 

Krypton Difluoride. Krypton difluoride [13773-81 -4] KrF is a colorless crystalline solid which can be sublimed under vacuum at 0°C but is thermodynamically unstable and slowly decomposes to the elements at ambient temperatures (Table 1). It can, however, be stored for indefinite periods of time at —78° C. The KrF molecule has been shown, like XeF2, to be linear in the gas phase, in the sofld state, and in solution. The standard enthalpy of... 

In both the Hquid and vapor states, phosphoms(III) oxide exists as the P40 molecule. The vapor of phosphoms(III) oxide ionizes air. Phosphoms tetroxide is made by heating P40 in a sealed tube to 440°C. P40 sublimes under vacuum at I80°C and forms colorless, glossy crystals. 

Titanium Trifluoride. The trifluoride (121) is a blue crystalline soHd, density 2980 kg/m, ia which the titanium atoms are six-coordinate at the center of a slightly distorted octahedron, where the mean Ti—F distance is 197 pm. Titanium trifluoride [13470-08-1] is stable ia air at room temperature but decomposes to titanium dioxide when heated to 100°C. It is insoluble ia water, dilute acid, and alkaUes but decomposes ia hot concentrated acids. The compound sublimes under vacuum at ca 900°C but disproportionates to titanium and titanium tetrafluoride [7783-63-3] at higher temperatures. 

Because phenols are weak acids, they can be freed from neutral impurities by dissolution in aqueous N sodium hydroxide and extraction with a solvent such as diethyl ether, or by steam distillation to remove the non-acidic material. The phenol is recovered by acidification of the aqueous phase with 2N sulfuric acid, and either extracted with ether or steam distilled. In the second case the phenol is extracted from the steam distillate after saturating it with sodium chloride (salting out). A solvent is necessary when large quantities of liquid phenols are purified. The phenol is fractionated by distillation under reduced pressure, preferably in an atmosphere of nitrogen to minimise oxidation. Solid phenols can be crystallised from toluene, petroleum ether or a mixture of these solvents, and can be sublimed under vacuum. Purification can also be effected by fractional crystallisation or zone refining. For further purification of phenols via their acetyl or benzoyl derivatives (vide supra). 

Bibenzyl [103-29-7] M 182.3, m 52.5-53.5 . Crystd from hexane, MeOH, or 95% EtOH. It has also been sublimed under vacuum, and further purified by percolation through columns of silica gel and activated alumina. 

Dimethoxybenzene [150-78-7] M 137.2, m 57.2-57.8 . Steam distd. Crystd from hexane or benzene, and from MeOH or EtOH but these are wasteful due to high solubilities. Dried under vacuum. Also sublimes under vacuum. 

Diphenylmethane [101-81-5] M 168.2, m 25.4°. Sublimed under vacuum, or distd at 72-75°/4mm. Crystd from EtOH. Purified by fractional crystn of the melt. 

Iodobenzoic acid [88-67-5] M 248.4, m 162 , pK 2.93. Crystd repeatedly from water and EtOH. Sublimed under vacuum at 100°. 

Isobutyramide [563-83-7] M 87.1, m 128-129 , b 217-221 . Crystd from acetone, benzene, CHCI3 or water, then dried under vacuum over P2O5 or 99% H2SO4. Sublimed under vacuum. 

V-Isopropylcarbazole [1484-09-9] M 209.3, m 120 . Crystd from isopropanol. Sublimed under vacuum. Zone refined. The picrate has m 143° after recrystn from EtOH. 

Methylaminoanthraquinone [82-38-2] M 237.3, m 166.5°, pK ,t-2. Crystd to constant melting point from butan-l-ol, then crystd from EtOH. It can be sublimed under vacuum. 

Naphthacene (benz[b]anthracene, 2,3-benzanthracene, rubene) [92-24-0] M 228.3, m >300 , 341 (open capillary), 349 , 357 . Crystd from EtOH or benzene. Dissolved in sodium-dried benzene and passed through a column of alumina. The benzene was evaporated under vacuum, and the chromatography was repeated using fresh benzene. Finally, the naphthacene was sublimed under vacuum. [Martin and Ubblehode J Chem Soc 4948 7967.] Also recrysts in orange needles from xylene and sublimes in vacuo at 186°. [UV Chem Ber 65 517 1932, 69 607 7956 IR Spectrochim Acta 4 373 7957.]... 

Nitrobiphenyl [86-00-0] M 199.2, m 36.7 . Crystd from EtOH (seeding required). Sublimed under vacuum. 

Pentaerythritol [115-77-5] M 136.2, m 260.5 . Refluxed with an equal volume of MeOH, then cooled and the ppte dried at 90°. Crystd from dil aq HCl. Sublimed under vacuum at 200°. 

Phthalazine [253-52-1] M 130.2, m 90-91°, pK ° 3.47. Crystd from diethyl ether or benzene, and sublimed under vacuum. 

Purified by repeated crystn from MeOH. It can also be purified by sublimation under vacuum. Purity can be checked by TLC using a mixed solvent (pet ether, diethyl ether, EtOH 10 10 1) on a silica gel plate. 

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.]... 

Crystd from EtOH or from benzene/abs EtOH, diethyl ether and pet ether. It was sublimed under vacuum and carefully dried in a vacuum line. Stored in the dark under nitrogen. 

Triphenylmethane [519-73-3] M 244.3, m 92-93 . Crystd from EtOH or benzene (with one molecule of benzene of crystallisation which is lost on exposure to air or by heating on a water bath). It can also be sublimed under vacuum. It can also be given a preliminary purification by refluxing with tin and glacial acetic acid, then filtered hot through a glass sinter disc, and ppted by addition of cold water. 

Antimony trifluoride [7783-56-4] M 178.8, m 292 . Crystd from MeOH to remove oxide and oxyfluoride, then sublimed under vacuum in an aluminium cup on to a water-cooled copper condenser [Woolf J Chem Soc 279 1955]. 

Several carboxylates, both simple salts and complex anions, have been prepared often as a means of precipitating the An ion from solution or, as in the case of simple oxalates, in order to prepare the dioxides by thermal decomposition. In K4[Th(C204)4].4Fl20 the anion is known to have a 10-coordinate, bicapped square antipris-matic structure (Fig. 31.8b). -diketonates are precipitated from aqueous solutions of An and the ligand by addition of alkali, and nearly all are sublimable under vacuum. [An(acac)4], (An = Th, U, Np, Pu) are apparently dimorphic but both structures are based on an 8-coordinate, distorted square antiprism. 

Electrolytic Mg is less pure than Mg obtained by thermal reduction methods and is purified commercially by sublimation under vacuum, a process inherent in thermal reduction. Typical analyses for crude electrolytic Mg (assay 99.8%), for sublimed material (assay 99.95%) and for twice sublimed material (assay 99.99%) are collected in Table l. Sublimation reduces most impurity levels (by 10 ) but leads to increased Zn content. 

Lyophillzation Hater sample is frozen and pure water is removed by sublimation under vacuum. Nonvolatile organics Can handle large sample volumes. Selective loss of volatile organics. Inorganic constituents concentrated simultaneously. 

Petrarch) was purified by melting and stirring in the presence of finely divided calcium hydride then sublimed under vacuum. The was then dissolved in purified cyclohexane and stored under N. ... 

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