Mixed silica gels

S.D. Sharma and C. Sharma, Retention behavior of inorganic anions on mixed silica gel G-starch layers quantitative separations of F, Mo042, As043", and Cr2072 from other anions. J. Planar Chromatogr.-Mod. TLC 16 (2003) 237-243. 

Meyer [60] has separated the various gallates and also other antioxidants, using hexane-acetic acid mixtures on mixed silica gel-kieselguhr layers (Fig. 178). Double development was shown to be advantageous. The method has been checked on examples from practice [89]. Fat-soluble dyes and other alcohol-soluble substances sometimes obstruct a one-dimensional separation and identification of the antioxidants, especially the gallates. Success has then been attained by two-dimensional TLC with the solvents chloroform and hexane-acetic acid. 

The layer is prepared by mixing silica gel GF245 (Merck) with 0.3 M sodium acetate solution, spreading into layers of about 250 pm thickness. Development is carried out twice to a height of 10 cm in a saturated chamber atmosphere, using chloroform-methanol (85 + 15). The spots are visualised by spraying with 10 ml of a freshly prepared 0.5% aqueous solution of Fast Blue B salt, followed some minutes later with a few ml of aqueous sodium hydroxide to intensify the colours. 

Table 16 A) /Values for Amino Acids on Copper Sulfate and Polyamide Mixed Silica Gel Plates ...

The values are average of two or more identical runs, 10 cm in 35 min. T, tailing A, untreated silica gel plate B, copper sulfate-impregnated silica gel C. polyamide mixed silica gel layers. Solvent, methanol-butyl acetate-acetic acid-pyridine (20 20 10 5). 

A solution of 2,3-dimethylindole (145 g, 1 mol) in dry dioxan containing hydroquinone (100 mg) was treated with JV,JV,JV-trimethylbenzylammonium ethoxide (5 ml of a 40% solution in MeOH) and warmed to 35 C. Freshly distilled acrylonitrile (150 ml, 2.5 mol) was added at a rate such that the temperature did not rise above 40°C. The solution was then stirred overnight and diluted with 10% aq. acetic acid (11). The solution was extracted with CH Clj and the extract was washed with water and dried (MgS04). extract was then mixed with silica gel (800 g) and the solvent removed in vacuo. The silica was placed in a Soxhlet extractor and extracted with cyclohexane. The extract deposited the product as colourless needles (125 g, 63% yield). 

To a stirred ice-cold solution of ethyl 3,6-dihydro-5-hydroxy-8-methyl-6-(phenylsulfonyl)benzo[l,2-b 4,3-b ]dipyrrole-l-carboxylate (368 mg, 0.85 mmol) in TEA (3ml) was added EtjSiH (1.5 ml), After 15 min the solution was allowed to come to room temperature and stirred for an additional 2h. The solution was evaporated in vacuo and the residue dissolved in CH2CI2 (10 ml), washed.with aq. NaHCOj and dried over MgS04. The solution was mixed with AcjO (1ml) and CH2C12 (1ml) and kept at room temperature for 2 h. The reaction mixture was evaporated and the residue purified by chromatography on silica gel using CHjClj-EtOAc (3 1) for elution. The product (271 mg) was obtained in 71 % yield. 

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. 

The enantioselective determination of 2,2, 3,3, 4,6 -hexachlorobiphenyl in milk was performed by Glausch et al. (21). These authors used an achiral column for an initial separation, followed by separation of the eluent fraction on a chiral column. Fat was separated from the milk by centrifugation, mixed with sodium sulfate, washed with petroleum ether and filtered. The solvent was evaporated and the sample was purified by gel permeation chromatography (GPC) and silica gel adsorption chromatography. Achiral GC was performed on DB-5 and OV-1701 columns, while the chiral GC was performed on immobilized Chirasil-Dex. 

The above crude bromohydrin was mixed with 2.5 grams of potassium acetate and 60 cc of acetone and refluxed for 6 hours, at the end of which the acetone was distilled, water was added to the residue and the product was extracted with methylene chloride. The extract was washed with water, dried over anhydrous sodium sulfate and the solvent was evaporated. Recrystallization of the residue from methanol furnished 800 mg of the 16,21-diacetate of 6o-fluoro-9(3,11(3-oxido-A -pregnene-16o,l7a,2l-triol-3,20-dione with MP 120° to 124°C by chromatography of the mother liquors on silica gel there was obtained 180 milligrams more of the same compound with MP 117° to 119°C. The analytical sample was obtained by recrystallization from methanol it showed MP 125° to 127°C. 

A solution of 0.7 g of 2-(2-amino-N-methylacetamido)-5-chlorobenzophenone in 10 ml of a 50% solution (by weight) of diketene in acetone is refluxed for 3 hours and then evaporated to give a brown oil. The oil Is chromatographed on 200 g of silica gel using a 1 1 (by volume) mixture of ethyl acetate cyclohexane 25 ml fractions are collected. Fractions 11-14 are combined, mixed with chloroform, evaporated and triturated with ether to give 0.337 g of 11-chloro-8,12b-dihydro-2,8-dimethy 1-12b-phenyl-4H-[ 1,3]oxazino[3,2-dl [1,4] benzodiazepine-4,7 (6H)-dione as a pale yellow solid, MP 174°C to 176°C. 

Mixed cellulose 10-undecenoate/U is(3,5-dimethyl-phenylcarbamate) bonded on silica gel [59,71] [51]... 

Purification of the activation products (PMs). The methylamine activation product dissolved in methanol is purified by chromatography, first on a column of silica gel using a mixed solvent of chloroform/ethanol, followed by reversed-phase HPLC on a column of divinylbenzene resin (such as Jordi Reversed-Phase and Hamilton PRP-1) using various solvent systems suitable for the target substance (for example, acetonitrile/water containing 0.15% acetic acid). 

The submitters mixed active anhydrous silica gel with water (12% v>/w) and stored it in a sealed container for at least 24 hours prior to use. A ratio of 60-80 g. of silica gel per gram of crude product was used for column chromatographic separations, and a column was chosen that would give a 10 1 height diameter ratio of adsorbent. Columns were wet-packed with distilled petroleum ether (b.p. 60-68c), and after the crude product had been applied a step-gradient was run rapidly through 2% vjv ether in petroleum ether, 5% ether, and 10% ether. The column was then eluted with 20% vjv ether in petroleum ether until the bromohydrin acetate was obtained. 

OF2 and H2S expld on mixing. Liq OF2 and 60/80 mesh silica gel at about. 254mm press and —196° expld. The presence of moisture was suspected (Ref 2)... 

A new approach to the resolution of sulphoxides 242 was recently reported by T oda and coworkers282. It takes advantage of the fact that some sulphoxides form crystalline complexes with optically active 2,2 -dihydroxy-l, 1-binaphthyl 243. When a two-molar excess of racemic sulphoxide 242 was mixed with one enantiomeric form of binaphthyl 243 in benzene-hexane and kept at room temperature for 12 h, a 1 1 complex enriched strongly in one sulphoxide enantiomer was obtained. Its recrystallization from benzene followed by chromatography on silica gel using benzene-ethyl acetate as eluent gave optically pure sulphoxide. However, methyl phenyl sulphoxide was poorly resolved by this procedure and methyl o-tolyl, methyl p-tolyl, s-butyl methyl and i-propyl methyl sulphoxides did not form complexes with 243. 

Flash column chromatography was performed using silica gel (10 cm diameter 27 cm height), eluting with 4/1 toluene/hexane. A small amount of aryl chloride that remained unreacted after 72 hr was recovered mixed with a small quantity (<5%) of the desired product. 

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