Sublimation fractional

Phthalic anhydride [85-44-9] M 148.1, m 132°, b 295°. Distd under reduced pressure. Purified from the acid by extracting with hot CHCI3, filtering and evaporating. The residue was crystd from CHCI3, CCI4 or benzene, or sublimed. Fractionally crystd from its melt. Dried under vacuum at 100°. [Saltiel 7 Am Chem Soc 108 2674 1986.]... 

The melting point of racemic 37 is 43 °C, therfore this racemate and DBTA monohydrate was mixed in 2 1 molar ratio as two powders at ambident temperature, then the mixture was subjected to fractionated sublimation in vacuum (Scheme 14). At 50 °C, the unreacted alkohol sublimated and it contained (1R,2R)-37 in excess. At higher temperature (up to 100 °C) the diastereoisomeric complex decomposed slowly and the second sublimated fraction was enriched in (1S,2S)-37 isomer. Results of one, two and three weeks reactions are summarised in Table 7. 

Prior to the advent of sophisticated mechanical and electrical instrumentation, the observation of thermal phenomena was restricted to systems which were amenable to detection by the human senses. Such observations included investigations of boiling or melting processes, sublimation, fractional crystallization, color changes and the occurrence of odors. With the invention of the thermometer, the first quantitative experiment was made possible. Development of thermometry led to "thermal analysis by recording the temperature of a test material as a function of time. Further developments led to calorimetry — the science of measuring quantities of heat. 

Method of purification Sublimation, fractional crystals from hot water. 

Rosenkrantz (1957) has written one of the earlier articles on the utilization of fractionation procedures with infrared analysis and has listed several types of fractionation techniques chromatography, countercurrent distribution, preferential solvent extraction, sublimation, fractional crystallization, molecular distillation, dialysis, centrifugation, electrophoresis, diffusion, and freeze-drying. He has also given references to work in which these methods have been used to fractionate a large variety of biological compounds. Elvidge and Sammes (1966) have discussed many of the techniques mentioned above. 

The so-called hydro-vac pump, shown in Fig. 11, 22, 2 (the upper half of the mercury reservoir and the column above it are insulated by a layer of asbestos), is an inexpensive, all-glass, mercury diffusion pump, which can be used in series either with an oil pmnp or with a water Alter pmnp (compare Fig. 11,21, 1) capable of producing a vacuum of at least 2 mm. It is accordingly of particular value in the organic laboratory for vacuum distillations, fractionations, sublimations and pyrolyses as well as for molecular distillations (see Section 11,26). The hydro-vac... 

Separations based upon differences in the physical properties of the components. When procedures (1) or (2) are unsatisfactory for the separation of a mixture of organic compounds, purely physical methods may be employed. Thus a mixture of volatile liquids may be fractionally distilled (compare Sections 11,15 and 11,17) the degree of separation may be determined by the range of boiling points and/or the refractive indices and densities of the different fractions that are collected. A mixture of non-volatile sohds may frequently be separated by making use of the differences in solubilities in inert solvents the separation is usually controlled by m.p. determinations. Sometimes one of the components of the mixture is volatile and can be separated by sublimation (see Section 11,45). 

In France, Compagnie Europnene du Zirconium (CEZUS) now owned jointly by Pechiney, Eramatome, and Cogema, uses a separation (14) based on the extractive distillation of zirconium—hafnium tetrachlorides in a molten potassium chloride—aluminum trichloride solvent at atmospheric pressure at 350°C. Eor feed, the impure zirconium—hafnium tetrachlorides from the zircon chlorination are first purified by sublimation. The purified tetrachlorides are again sublimed to vapor feed the distillation column containing the solvent salt. Hafnium tetrachloride is recovered in an enriched overhead fraction which is accumulated and reprocessed to pure hafnium tetrachloride. 

Currently, there is continuing work on an iadustry standard method for the direct determination of monomer, dimer, and trimer acids. Urea adduction (of the methyl esters) has been suggested as a means of determining monomer ia distilled dimer (74). The method is tedious and the nonadductiag branched-chain monomer is recovered with the polymeric fraction. A micro sublimation procedure was developed as an improvement on urea adduction for estimation of the polymer fraction. Incomplete removal of monomer esters or loss of dimer duriag distillation can lead to error (75). 

The melting point of indazole has been reported at various temperatures in the range of 145 to 149 °C. Indazole boils at 269-270 °C at 743 mmHg and 146 °C at 15 mmHg, can be readily sublimed on a water bath and is also steam-volatile. Its two A-methyl derivatives have similar melting points 1-methyl (106), m.p. 61 °C, 2-methyl (107), m.p. 56 °C, but they are easily separated by fractional distillation [(106), 120/15 (107), 141/15]. 

Benzo-(a)-pyrldo- 4,3,h>-ecrldlne (3). To e mixture of S-amuKiisoquinolins 1 (1 5 g, 11 mmol) and p-naphlol 2 (1 5 g, 10 mmol) hesled lo 250°C, was added in small portions paraformaldehyde (0.4S g, ISO mmol) when stesm had ceased lo evolve, the mixture was healed tor a lew more minutes then fractionated in vacuum. The thick resin (bp 200°C-11 mm) was collected arxJ recrystelllized from BuOH. A final purificalion was effected by vecuum sublimation lo afford 1.3 g of 3 (46%), mp 289°C. 

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). 

Common impurities found in aldehydes are the corresponding alcohols, aldols and water from selfcondensation, and the corresponding acids formed by autoxidation. Acids can be removed by shaking with aqueous 10% sodium bicarbonate solution. The organic liquid is then washed with water. It is dried with anhydrous sodium sulfate or magnesium sulfate and then fractionally distilled. Water soluble aldehydes must be dissolved in a suitable solvent such as diethyl ether before being washed in this way. Further purification can be effected via the bisulfite derivative (see pp. 57 and 59) or the Schiff base formed with aniline or benzidine. Solid aldehydes can be dissolved in diethyl ether and purified as above. Alternatively, they can be steam distilled, then sublimed and crystallised from toluene or petroleum ether. 

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). 

Benzoic acid [65-85-0] M 122.1, m 122.6-123.1, pK 4.12. For use as a volumetric standard, analytical reagent grade benzoic acid should be carefully fused to ca 130 (to dry it) in a platinum crucible, and then powdered in an agate mortar. Benzoic acid has been crystd from boiling water (charcoal), aq acetic acid, glacial acetic acid, C6H6, aq EtOH, pet ether (b 60-80 ), and from EtOH soln by adding water. It is readily purified by fractional crystn from its melt and by sublimation in a vacuum at 80. ... 

Benzoquinoline (phenanthridine) [229-87-8] M 179.2, m 108-109 , b 350 , pK 4.61. Chromatographed on activated alumina from benzene soln, with diethyl ether as eluent. Evapn of ether gave crystalline material which was freed from residual solvent under vacuum, then further purified by fractional crystn under N2, from its melt. Sublimes in vacuo. See also p. 324. 

Dimethylphenol [576-26-1] M 122.2, m 49°, b 203°/760mm, pK 10.61. Fractionally distd under nitrogen, crystd from benzene or hexane, and sublimed at 38°/10mm. 

Difficult to distil because it is a solid at ambient temperatures. Purified by fractional crystallisation and sublimation. 

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. 

Nitronaphthalene [86-57-7] M 173.2, m 57.3-58.3 , b 30-40 /0.01mm. Fractionally distd under reduced pressure, then crystd from EtOH, aqueous EtOH or heptane. Chromatographed on alumina from benzene/pet ether. Sublimes in vacuo. 

Sublimed under high vacuum, or dried under a current of HCl gas, followed by fractional distn, once under HCl and once under argon. 

Preparation of 1 -(/3-D-arabinofuranosyl)-2-thiocytosine A solution of 2.0 g of 1 -(2, 3, 5 -0-triacetyl-/3-D-arabinofuranosyl)-2,4-dithiouracil in 100 ml of methanol is saturated with anhydrous ammonia at 0°C. The mixture, in a glass liner, is heated in a pressure bomb at 100°C for three hours. The reaction mixture is concentrated to a gum in vacuo, and most of the byproduct acetamide is removed by sublimation at 60°C/0.1 mm. The residue is chromatographed on 100 g of silica gel. Elution of the column with methylene chloride-methanol mixtures with methanol concentrationsof 2-25% gives fractions containing acetamide and a series of brown gums. The desired product is eluted with 30% methanol-methylene chloride to give a total yield of 0.386 g (30%), MP 175°-180°C (dec.). Recrystallization from methanol-iso-propanol furnishes an analytical sample, MP 180°-182°C (dec.). 

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