Chromatography, on alumina

Cls-l,2,3,3a,4,8b-Hexahydro-4-forinyl-8b-ethylcyclopent(b)lndole. (2). Pheny iydra2one 1 (850 tng, 4.2 mmol) was trealed w ith98% HCOOH (902 mg, 19.6 mmol), 8era short exothermic reaction the mixture was heated at 130-135°C for 35 min. Evaporation HCOOH, extraction with EtOAc arxt chromatography on alumina (PhH) aflorded 246 mg i (25.6%). 

The progress of the reaction may be followed by analytical thin-layer chromatography on alumina. The submitters used polygram pre-coated plastic sheets (Alox N/UV254) purchased from Macherey-Nagel, Inc. The plates were developed with 1 1 hexane-ether and stained with basic permanganate. The Rf of the product is 0.56. 

Aminophenol [123-30-8] M 109.1, m 190 (under N2), pKj 5.38, pKj lO.4. Crystd from EtOH, then water, excluding oxygen. Can be sublimed at 110°/0.3mm. Has been purified by chromatography on alumina with a 1 4 (v/v) mixture of absolute EtOH7 benzene as eluent. 

Astacin (P,P-carotene-3,3, 4,4 -tetraone) [514-76-1] M 592.8, m 228", 240-243"(evacuated tube), 550,000 at 498mm (pyridine). Probable impurity is astaxanthin. Purified by chromatography on alumina/fibrous clay (1 4) or sucrose, or by partition between pet ether and MeOH (alkaline). Crystd from pyridine/water. Stored in the dark under N2 at -20°. [Davis and Weedon J Chem Soc 182 I 960.]... 

Azobenzene [103-33-3] M 182.2, m 68", pK 2.48. Ordinary azobenzene is nearly all in the transform. It is partly converted into the cw-form on exposure to light [for isolation see Hartley J Chem Soc 633 1938, and for spectra of cis- and /ran5-azobenzenes, see Winkel and Siebert Chem Ber 74B 6707947]. trans-Azobenzene is obtained by chromatography on alumina using 1 4 benzene/heptane or pet ether, and crystd from EtOH (after refluxing for several hours) or hexane. All operations should be carried out in diffuse red light or in the dark. 

Diazoaminobenzene (1,3-diphenyltriazene) [136-36-6] M 197.2, m 99 . Crystd from pet ether (b 60-80°), 60% MeOH/water or 50% aqueous EtOH (charcoal) containing a small amount of KOH. Also purified by chromatography on alumina/toluene and toluene-pet ether. Stored in the dark. 

Dibenzothiophene [132-65-0] M 184.3, m 99 . Purified by chromatography on alumina with pet ether, in a darkened room. Crystd from water or EtOH. 

Dimethylbenz[from acetone/EtOH. 

Dinitroaniline [606-22-4] M 183.1, m 139-140 , pK -5.37 (aq H2SO4). Purified by chromatography on alumina, then crystd from benzene or EtOH. 

Dioctadecyldimethylammonium bromide [3700-67-2] M 630.9, m 161-163 . Crystd from acetone then MeOH [Lukac J Am Chem Soc 106 4387 1984]. Also purified by chromatography on alumina by washing with CgHg and eluting with Me2CO, evap and cryst from MeCN [Swain and Kreevoy J Am Chem Soc 77 1126 1955]. 

Tetra-4 -pyridinylporphyrin [16834-13-2] M 618.7, m >300°(dec). Purified by chromatography on alumina (neutral. Grade I), followed by recrystn from CH2Cl2/MeOH [Yamashita et al. J Phys Chem 91 3055 1987]. 

Triphenylbenzene [612-71-5] M 306.4, m 173-175 . Purified by chromatography on alumina using benzene or pet ether as eluents. 

Commercial material contains up to 4% desmethylcolchicine. Purified by chromatography on alumina, eluting with CHCI3 [Ashley and Harris J Chem Soc 677 1944]. Alternatively, an acetone solution on alkali-free alumina has been used, and eluting with acetone [Nicholls and Tarbell J Am Chem Soc 75 1104 1953]. 

From hen egg white. Purified by solvent extraction and chromatography on alumina. Suspended in distilled water and kept frozen until used [Lee and Hunt J Am Chem Soc 106 7411 1984, Singleton et al. J Am Oil Chem Soc 42 53 7965]. For purification of commercial egg lecithin see Pangborn [J Biol Chem 188 471 7957]. 

The mixture of diastereomers has been separated into its two principal components by Izatt, Haymore, Bradshaw and Christensen who had previously identified the two principal diastereomers as the cis-syn-cis and cis-anti-cis isomers. Their previous separation technique involved a protracted chromatography on alumina but the new method relied upon the difference in water solubility between the lead perchlorate and hydroniur perchlorate complexes. The lead perchlorate complex is essentially insoluble in aqueous solution and precipitates from it. Using this method, one may obtain 39% of the high-melting polymorph (mp 83—84°) and 44% of the low-melting compound (mp 62—63°). Note that the former also exists in a second crystalline form, mp 69—70°. 

A solution of cholest-4-en-3-one (139), 1 g, in diethylene glycol dimethyl ether (20 ml) is treated for 1 hr with a large excess of diborane at room temperature under nitrogen and then left for a further 40 min. Acetic anhydride (10 ml) is added and the solution refluxed for 1 hr. The mixture is concentrated to a small volume, diluted with water and extracted with ether. The extracts are washed with 10% sodium hydroxide solution, then with water and dried over sodium sulfate. Removal of the solvent leaves a brown oil (1.06 g) which is purified by chromatography on alumina (activity I). Hexane elutes the title compound (141), 0.68 g mp 76-77°. Successive crystallization from acetone-methanol yields material mp 78-79°, [a]p 66°. 

The latter compound can be isolated from the reaction mixture by chromatography on acid-washed alumina. Similar treatment of the trans-ketone (117a) followed by isolation and chromatography on alumina gives the same equilibrium mixture. The structure of the thermodynamically more stable ketone (116a) was proved by its conversion by Wolff-Kishner reduction to the hydrocarbon (118) independently synthesized from the known... 

Indeed, great emphasis was placed on the presentation of compounds in crystalline form for many years, early chromatographic procedures for the separation of natural substances were criticized because the products were not crystalline. None the less, the invention by Tswett (3) of chromatographic separation by continuous adsorption/desorption on open columns as applied to plant extracts was taken up by a number of natural product researchers in the 1930s, notably by Karrer (4) and by Swab and lockers (5). An early example (6) of hyphenation was the use of fluorescence spectroscopy to identify benzo[a]pyrene separated from shale oil by adsorption chromatography on alumina. 

Method A A solution of the azidoquinoline (5 mmol) in 3M KOMe in MeOH (40 mL) and dioxane (40 mL) was irradiated under N2 using a water-cooled, 125-W medium-pressure Hg lamp until all the azide [as measured by the disappearance of u(N3) at 2120 cm" 1 or by TLC] had reacted (4-10h). The photolysate was left to stand at 20 C for 24h then neutralized cautiously by the addition of 4M IICI in MeOH. The solvent was removed under reduced pressure and the crude product was purified initially by column chromatography on alumina (Type H, toluene), then finally by crystallization (petroleum ether). 

In contrast, transmetalation of the lithium enolate at —40 C by treatment with one equivalent of copper cyanide generated a species 10b (M = Cu ) that reacted with acetaldehyde to selectively provide a 25 75 mixture of diastereomers 11 and 12 (R = CH3) which are separable by chromatography on alumina. Other diastereomers were not observed. Similar transmetalation of 10a (M = Li0) with excess diethylaluminum chloride, followed by reaction with acetaldehyde, produced a mixture of the same two diastereomers, but with a reversed ratio (80 20). Similar results were obtained upon aldol additions to other aldehydes (see the following table)49. 

As reported by Shani and Sondheimer,1 the dehydrohalogenation of the tetrabromide by means of potassium hydroxide in ethanol at 50-55° affords a mixture, which is readily separated by chromatography on alumina, of l,6-oxido[10]annulene and the isomeric 1-benzo-xepin. The latter compound is also formed during chromatography of l,6-oxido[10]annulene on silica gel.7... 

The adsorption mechanism in chromatography on alumina differs from that on silica gel because of the structural differences between these adsorbents. Relationships between the values of solutes and the adsorption data for the mobile phase components on sihca gel G and alumina G have been investigated by Rozylo [64,65]. The theoretical and experimental results obtained by the relation 2 = /( 1) show a good agreement for the two adsorbents. 

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