Sublimation isolation procedure

We find it quite easy to isolate the sublimed product without the use of a drybox. The isolation procedure is as follows. The su-blimer is positioned horizontally, the stopper at the top is removed and with (Ar) flowing out of the flask the crystals are scraped from the walls and powdered using a stainless steel spatula. The product is then transfered to a storage flask connected through the side arm. 

Fazio et al. [927] have described a multideterminative procedure for various antioxidants (DLTDP, BHT, lonox 100, PG, BHA) in food by means of a (10 " mm Hg) vacuum sublimation technique (with GC and confirmed by UV, IR or MS) and achieved recoveries exceeding 85%. Although no indications were given that this isolation procedure would be equally successful for the quantitative determination of these indirect food additives when incorporated in a polymeric matrix, Shlyapnikov et al. [928] have reported the direct determination of AOs in PE by vacuum sublimation. 

Illudin M (I) was first isolated from Clitocyhe illudens, strain 72027-S, in low yield (Anchel, Hervey and Robbins, 1950 see previous section). Later (1952), these workers found that strain 14610-S produced more illudin M (I) relative to illudin S (II) the ratio of the former to the latter was 1.29 1 in this strain. This allowed the use of a much simpler isolation procedure On extraction with chloroform and evaporation of the chloroform, shghtly impure illudin M (I) crystallized, and could be purified by sublimation to yield 0.22 g/1 of culture medium. 

In a typical Knof procedure, 3jS-hydroxyandrost-5-en-17-one acetate is epoxidized with perbenzoic acid (or m-chloroperbenzoic acid ) to a mixture of 5a,6a- and 5)5,6)5-epoxides (75) in 99 % yield. Subsequent oxidation with aqueous chromium trioxide in methyl ethyl ketone affords the 5a-hydroxy-6-ketone (76) in 89% yield. Baeyer-Villiger oxidation of the hydroxy ketone (76) with perbenzoic acid (or w-chloroperbenzoic acid ) gives keto acid (77) in 96% yield as a complex with benzoic acid. The benzoic acid can be removed by sublimation or, more conveniently, by treating the complex with benzoyl chloride and pyridine to give the easily isolated )5-lactone (70) in 40% yield. As described in section III-A, pyrolysis of j5-lactone (70) affords A -B-norsteroid (71). Knof used this reaction sequence to prepare 3)5-hydroxy-B-norandrost-5-en-17-one acetate, B-noran-... 

In a procedure identical to that described in Section B, the reaction is performed using 2.5 g (7.1 mmol) of hexacarbonyltungsten (Alfa) and 1.66 g (14.2 mmol) of nitrosyl tetrafluoroborate (Aldrich, sublimed 220 °C, 10-3 torr) An emerald green complex is isolated to yield 3.95 g (96%) of cis-tetrakis-(acetonitrile)dinitrosyltungsten(II) bis[tetrafluoroborate(l —)]. 

Although the concentration of fluorine is the most important quantity in the control of the reaction rate and must be maintained within certain limits, in practice the stoichiometry, the molecular fluorine to substrate H-atom molar ratio, is used to determine the reaction parameters leading to a successful and efficient perfluorination. AF is most successful when sublimable solids are introduced into the hydrocarbon evaporator unit of the aerosol fluorinator as solutions by a syringe pump. This now common procedure emphasizes the individual molecule s isolation as it is fluorinated using AF. No intermolecular reactions between solute and solvent have been observed Choice of the solvent is important as it must not boil at a temperature below the melting point of the solute in order to prevent solid deposition in the tubes feeding the evaporator. It must also fluorinate to a material easily separable from the solid reactant after perfluorination. In most cases it has been found that aliphatic hydrochlorocarbons are excellent choices, but that carbon tetrachloride and chloroform and other radical-scavenging solvents are not (sec ref 6). 

In general preparative work, the chromatographic techniques cited above may be used (a) to establish the purity and authenticity of starting materials and (if appropriate) reagents (b) to monitor the reaction, particularly in the case of new reactions, or in the optimisation of experimental conditions to achieve the highest possible yield of product (c) to check the isolation and purification procedures (d) to achieve the separation of product mixtures should this not be possible by means of distillation, recrystallisation, or sublimation procedures (e) to provide a further check on the authenticity of the final product in addition to that provided by the comparison of physical constants (e.g. m.p., b.p., d, [a]n, etc.) and spectroscopic data with those quoted in the literature. 

Representative Procedure for the Palladium-Catalyzed Arylation of Amines with Aryl Bromides using DPPF/Pd (Excerpted with permission from [29]. 1996 American Chemical Society) In an inert atmosphere dry box, DPPFPdClj and 3.0 equiv. of DPPF/Pd were added to a solution of 20 equiv of bromoben-zophenone and 25 equiv of sodium ferf-butoxide in 8 ml of anhydrous THF. The reaction tube was sealed with a cap containing a PTFE septum and removed from the dry box. Butylamine (25 equiv) was added to the reaction mixture by syringe, and the mixture was heated to 100 °C for 3 h. The reaction was cooled to room temperature, the volatile materials were removed by rotary evaporation, and the product was isolated by either sublimation or silica-gel chromatography (20 1 hexane/EtOAc or 10 1 hexane/Et20 followed by 4 1 hexane Et20). 

The RMgX is added to a suspension of the Ni salt in ether at low T. When the reaction is complete, the solvent is evaporated and the product isolated by crystallization from pentene or by sublimation. The resultant bis(allyl)nickel derivatives have limited thermal stability decomposition occurs between 20°C and — 30°C depending on the nature of the substituents (see Table 4). A procedure is available for Ni(i -C3H5)2 Alternatively, the... 

PcZn was prepared after a slightly modified known procedure [37] DBU (0.76 g, 5 mmol) was added to a mixture of sublimed phthalonitrile (0.64 g, 5 mmol) and dry zinc(II) acetate (0.23 g, 1.25 mmol) in dry n-pentanol (20 mL). The mixture was heated for 36 h under reflux. Methanol (50 mL) was added. The isolated product was washed with water and methanol, and then treated with methanol in a Soxhlet apparatus overnight. Yield 0.54 g (75%). The dried PcZn was then purified by zone sublimation at 10 -10 mbar and 370 °C. UVA is (thf) = 666 nm. MS (DCI, negative, NH3) miz 576... 

Despite the very early claims for its preparation, 9S3 eluded synthesis until 1977, when Ochrymowycz and coworkers prepared it in heartbreakingly low yield (0.04%) from the reaction of ethylene chloride with sodium 3-thiapentane-l,5-dithiolate in EtOH (Table 4) [11]. Subsequently, Glass and coworkers [62] improved the yield to 4.4% through use of BzMe3N OMe to deprotonate 3-thiapentane-1,5-dithiol for reaction with ethylene chloride (Table 4). Application of the cesium carbonate procedure (for the same reactants in DMF) affords 9S3 in 50% yield [59]. Sublimation of ligand from the crude reaction mixture greatly facilitates the isolation of what historically has been the most elusive of all the crown... 

Purpose. To extract the active principle, an alkaloid, caffeine, from a native source, tea leaves. Caffeine is a metabolite (a product of the living system s biochemistry) found in a variety of plants. We wtU use ordinary tea bags as our source of raw material. This experiment illustrates an extraction technique often used to isolate water-soluble, weakly basic natural products from their biological source (see also Experiment [llA] for another extraction strategy). The isolation of caffeine win also give you the opportunity to use sublimation as a purification technique, since caffeine is a crystalline alkaloid that possesses sufficient vapor pressure to make it a good candidate for this procedure. In addition, the preparation of a derivative of caffeine, its 5-nitrosalicylate salt, will be carried out. This latter conversion takes advantage of the weakly basic character of this natural product. 

---