Column chromatography eluant

Three general methods exist for the resolution of enantiomers by Hquid chromatography (qv) (47,48). Conversion of the enantiomers to diastereomers and subsequent column chromatography on an achiral stationary phase with an achiral eluant represents a classical method of resolution (49). Diastereomeric derivatization is problematic in that conversion back to the desired enantiomers can result in partial racemization. For example, (lR,23, 5R)-menthol (R)-mandelate (31) is readily separated from its diastereomer but ester hydrolysis under numerous reaction conditions produces (R)-(-)-mandehc acid (32) which is contaminated with (3)-(+)-mandehc acid (33). 

This material should be at least 98% pure by vapor-phase chromatography (SE-30 column at 180-200°). It usually crystallizes if stored in a refrigerator. Unreacted hexamethylbenzene, present if insufficient oxidant is used, can best be removed by column chromatography on alumina with pentane as eluant. 

Pure syn product, free of anti isomer, can be obtained by column chromatography over silica gel (230-400 mesh) using the same 3-component eluant as for analysis (Note 7). 

The crude product was sufficiently pure and used as such for the next step (purification by column chromatography using hexanes EtOAc, 4 6 as an eluant affords... 

Salicylic acid and Its metabolite were separated by two methods. The first was thin layer chromatography on cellulose with BAW solvent as for the In vivo metabolism studies. A quicker separation was achieved with a polyamide column. The entire 400 pL from an individual assay was placed on top of a 0.8 x 2.0 cm column packed with Polyamide-6 (Accurate Chemical and Scientific Corp.). The salicylic acid metabolite was eluted with 6 mL water but salicylic acid was retained. 3a70B scintillation fluid (Research Product International Corp.) was used to determine the radioactive content of the entire 6 mL of eluant. Separation of salicylic acid and its metabolite by polyamide column chromatography was verified by thin layer chromatography. 

To a solution of 1.97 g (10 mmol) of 2-butynyl diisopropylcarbamate in 30 mL of diethyl ether under nitrogen at —78 °C are added 6.9 mL (11 mmol) of 1.6 M butyllithium via a syringe. After 15 min at — 70 °C, 3.12 g (11 mmol) of titanium(IV) isopropoxide in hexane are added and the mixture is stirred for 1.5 h at between — 70 and — 78 C. After raising the temperature to 0 °C the reaction mixture is poured into a mixture of 50 g of ice, 50 mL of 2 M hydrochloric acid and 100 mL of diethyl ether. The aqueous layer is extracted with two 50-mL portions of diethyl ether, and the ethereal solutions are washed with 50 mL of water, 50 mL of sat. aq NaHCOj/KCl and dried over MgS04. The solvent is evaporated in vacuo and the residue purified by column chromatography over silica with diethyl ether/hexane 1 5 as eluant yield 2.15 g (89%) mp 48 C. 

In some preparations Na[H30s4(C0)i2] is present as byproduct it can be removed by column chromatography on silicagel (column diameter 20 mm, length 200 mm) using acetone hexane (4 1) as eluant in these cases, yields of Na2[H40sio(CO)24] are approximately 50%. 

The packing material is Silica Gel 60, Cat 7734 (70-230 mesh ASTM), for column chromatography, an EM Reagent of E. Merck, Darmstadt, available from Brinkmann Instruments Ltd. (Canada). Lower grades of silica gel such as the 60-120 mesh grade of BDH Chemicals Ltd. were found to be much less efficient, not effecting a complete separation of the compounds. The amount of Silica Gel 60 utilized, 75 g., or 8.5 g. of silica gel per g. of reaction mixture, was found to be the most efficient. The checkers used Mallinckrodt CC-7 Special (100-200 mesh) column packing, a flow rate of 8.5 ml. per minute and a 9 1 ratio of hexane-chloroform eluant. A lower product yield (77%) resulted. 

The solution is evaporated to dryness under reduced pressure and the residue is purified by thin layer chromatography (PF-254G silica gel with 1 4 dichloromethane-hexane eluant). Three yellow bands are eluted. The second band is removed and product extracted from it is recrystallized from hexane. Yield 0.12-0.15 g (30-33%) of the desired product. Checkers used column chromatography (35 x 3-cm column, Silica Gel 60, 70-230mesh, Merck) to give the product as the second band when eluting with 1 4 dichloromethane-hexane. 

The oily liquid was purified by column chromatography (silica gel, 80 mesh eluant, petroleum ether) and distilled. A colorless oily liquid (b.p., 123°-125°C./0.5 mm. Hg, nD20 1.5530) was obtained. The infrared spectrum was that of 3-cyclohexylcyclohexene. 

Irradiation procedures. Mesophase solutions and neat solid samples of BN were prepared and sealed under N2 or vacuum in Kimax capillary tubes. Isotropic samples were either degassed (freeze-pump-thaw techniques) and sealed in pyrex tubes or saturated with N2 in pyrex tubes. Nitrogen was bubbled through the latter solutions during irradiation periods. When ther-mostatted, samples were placed in a temperature controlled ( 1°) water bath. All samples were irradiated with a 450 W Hanovia medium pressure Hg arc and were stored at -30°C until their futher use. Usually, a "dark sample was prepared and treated in an identical fashion to the irradiated samples except that it was shielded from the light. JSN from each tube was recovered by either column chromatography (silica or alumina and pentane eluant) at 4°C followed by solvent removal at 0°C and reduced pressure or by hplc (tr-hexane) at room temperature followed by solvent removal at 0°C and reduced pressure. Neat solid samples were dissolved in one of either benzene, tetrahydrofuran or toluene and were frozen until analyzed. 

The submitters used medium pressure chromatography5 on 25 x 1000 urn of 230-400 mesh silica gel with a 25 x 250 mm scrubber column. The eluant (3 1 1 hexane ethyl acetate methylene chloride) was passed through the column at a rate of 15 mL/min, collecting 15 mL fractions. The checkers were unable to obtain pure product using a gravity column or flash chromatography. 

The mother liquors from Step C above were purified by column chromatography on silica gel using 10% ethyl acetate in hexanes as eluant. The pure, undesired diastereomer (a colorless foam) was hydroylzed according to Step D. The enantiomeric benzoxazinone, (+)-6-chloro-4-cyclopropylethynyl-4-trifluoromethyl-l,4-dihydro-2H-3,l-benzoxazin-2-one, was obtained as white crystals. Melting point 131°-132°C [a]D20 =+84.4° (CHCI3, c=0.005 g/mL). 

A solution of 23.9 g (100 mMol) of methyl 3,4-diaminobenzoate dihydrochloride and 11.7 g (110 mMol) of butyric acid chloride in 100 ml of phosphorus oxychloride is refluxed for 2 h. Then about 80 ml of phosphorus oxychloride are distilled off and the residue is mixed with about 150 ml of water. The oily crude product precipitated is extracted three times with 50 ml of ethyl acetate and after evaporation purified by column chromatography (600 g of silica gel eluant methylene chloride/methanol (30 1)). Yield of methyl-2-n-propyl-benzimidazole-5-carboxylate 15.0 g of oil (69%). 

A solution of 6.7 g (25 mMol) of 2-n-propyl-benzimidazole-5-carboxylic acid-hemisulphate and 4.9 g (25 mMol) of 2-methylaminoaniline dihydrochloride in 200 g of polyphosphoric acid is stirred for 5 h at 150°C, then poured onto 600 ml of water and made alkaline with concentrated ammonia whilst cooling with ice. The resulting solution is extracted three times with 200 ml of ethyl acetate, the crude product thus obtained is purified by column chromatography (300 g of silica gel eluant methylene chloride/methanol = 15 1). Yield of 2-n-propyl-5-(l-methylbenzimidazol-2-yl)-benzimidazole 2.8 g of oil (39%). 

A solution of the alkene (10 mmol) and DIB (6.4 g, 20 mmol) in dry dichloro-methane (250 ml) was cooled to — 20°C. To this a solution of trimethylsilyl azide (4.6 g, 40 mmol) in dichloromethane (50 ml) was added slowly. The homogeneous mixture was allowed to stand at - 20°C for 12-16 h and for a further 12 h at room temperature. The reaction mixture was washed with water and a saturated solution of sodium bicarbonate, dried and concentrated. The azidoketone was obtained by column chromatography (silica gel, petroleum ether-acetone, 9 1 or other suitable eluant). 

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