Silica saturator columns

Separation of Lipid Classes. Lipid classes were separated according to Singleton and Stikeleather (4) on a silica column (25 X 0.46 cm, 5 pm, Luna, silica (2), Phenomenex, Torrance, CA) with a linear gradient of 2-propanol/hexane (4 3, vol/vol) to 2-propanol/hexane/water (4 3 0.75, by vol) in 20 min, then isocratically for 20 min. A prepacked silica saturator column (3 x 0.46 cm, 15-25 pm, Phenomenex) was installed between the pump and injector to saturate the mobile phase with silica before it reached the column. 

Dibenzyl-14-crown-4 (lithium ionophore VI 6,6-dibenzyl-l,4,8,ll-tetra-oxa-cyclo-tetradecane) [106868-21-7] M 384.5, m 102-103°. Dissolve in CHCI3, wash with saturated aqueous NaCl, dry with MgSOa, evaporate and purify by chromatography on silica gel and gradient elution with C6Hg-MeOH followed by preparative reverse phase HPLC on an octadecyl silanised silica (ODS) column and eluting with MeOH. It can be crystd from MeOH (v Br 120 cm , C-O-C). [7 Chem Soc Perkin Trans 1 1945 1986.]... 

A mixture of 4.98 g of acetoacetic acid N-benzyl-N-methylaminoethyl ester, 2.3 g of aminocrotonic acid methyl ester, and 3 g of m-nitrobenzaldehyde was stirred for 6 hours at 100°C in an oil bath. The reaction mixture was subjected to a silica gel column chromatography (diameter 4 cm and height 25 cm) and then eluted with a 20 1 mixture of chloroform and acetone. The effluent containing the subject product was concentrated and checked by thin layer chromatography. The powdery product thus obtained was dissolved in acetone and after adjusting the solution with an ethanol solution saturated with hydrogen chloride to pH 1 -2, the solution was concentrated to provide 2 g of 2,6-dimethyl-4-(3 -nitrophenyl)-1,4-dihydropyridlne-3,5-dicarboxylic acid 3-methylester-5- -(N-benzyl-N-methylamino)ethyl ester hydrochloride. The product thus obtained was then crystallized from an acetone mixture, melting point 136°Cto 140°C (decomposed). 

This temperature is gradually raised to 95°C and the mixture kept at this temperature for 1 hour. The mixture is allowed to cool and added to 2 liters of water. The aqueous layer is extracted with ether, the ether solution washed twice with saturated sodium chloride solution, 5% Na2C03 solution, water, and then dried. The ether filtrate is concentrated with 200 grams silica-gel, and added to a five pound silica-gel column packed with 5% ether-petroleum ether. The column is eluted with 5 to 10% ether-petroleum ether and followed by TLC to give 6-fluoro-2-methylindanone. 

Resins 2 and 3 are treated with dichloromethane containg 3% and 1.5% trifluoroacetic acid (lOmL/g resin), respectively, for 18 h. The resin is filtered off and washed twice with dichloromethane (10 mL / g of resin). The filtrate is washed with saturated NaHCCL (5 mL) and brine (5 mL), and the organic phase is separated and filtered through a short path silica gel column to obtain a colourless solution. In the case of polymer-bound allyl esters giving rise to cleavage products of type 5f, the aqueous workup is omitted. The products obtained after removal of solvent under reduced pressure contain small amounts of silanol by-products (note 5), which is to be accounted for in the calculation of cleavage yields. 

Normal-phase liquid chromatography is thus a steric-selective separation method. The molecular properties of steric isomers are not easily obtained and the molecular properties of optical isomers estimated by computational chemical calculation are the same. Therefore, the development of prediction methods for retention times in normal-phase liquid chromatography is difficult compared with reversed-phase liquid chromatography, where the hydrophobicity of the molecule is the predominant determinant of retention differences. When the molecular structure is known, the separation conditions in normal-phase LC can be estimated from Table 1.1, and from the solvent selectivity. A small-scale thin-layer liquid chromatographic separation is often a good tool to find a suitable eluent. When a silica gel column is used, the formation of a monolayer of water on the surface of the silica gel is an important technique. A water-saturated very non-polar solvent should be used as the base solvent, such as water-saturated w-hexane or isooctane. 

Silica-based anion-exchangers tend to have short life-times. This may be extended somewhat by proper sample clean-up and by the use of a silica-gel-saturation column, but this rapid degradation remains the biggest disadvantage of these phases. The resin-based phases are very stable, unless operated above 65°. Unfortunately, because of the slow diffusion processes in these resins, they must be operated at higher temperatures in order to achieve good efficiencies. 

The effect of the quality of the solvent has also been investigated in terms of the saturates content (14). This was prompted by some similar work carried out by Kimber (15). The saturates content of the HAO is measured by the quantity of material passing through a silica gel column with n-pentane as eluent. Generally, as saturate levels increase, the amount of donatable hydrogen in the solvent decreases and the conversion decreases. However, it was also found that as saturate levels increase the ash level in the filtered extract solution decreases. Some results using Calverton coal are shown in Table 4. The HAO samples used were made up by mixing, in the required proportions, the 8 and 22 % samples. 

A 300-ml flask was charged with the step 1 product (1.00 g) suspended in 10 ml of THF and then cooled to 0°C and treated with the entire Grignard reagent and the mixture refluxed for 5 hours. The mixture was cooled and treated with 10 ml of water/hydrochloric acid and a two-phase solution obtained. The organic phase was isolated and washed with water and saturated saline, dried over Na2S04, concentrated, and 1.65 g of residue obtained. The residue was purified by silica gel column... 

A flask was charged with the step 3 product (6.1 mmol) and 50 ml diethyl ether and then cooled to — 90°C and treated with the dropwise addition of 8.4 ml -butyl lithium (1.6 M -hexane solution 13.4 mmol). After 1 hour of stirring the mixture was treated with sulfur (6.1 mmol). The temperature was then raised to ambient temperature for 1 hour and then treated with additional sulfur (6.1 mmol) and stirred for 3.5 hours. The mixture was then treated with the dropwise addition of 15 ml of 1M hydrochloric acid. The aqueous phase was extracted with diethyl ether, the organic layer collected, washed with water and saturated brine aqueous solution, and dried. The mixture was concentrated and the residue purified by silica gel column chromatography using hexane/ethyl acetate, 20 1, respectively, and 0.91 g of product isolated. 

To a stirred mixture of 14 [39] (493 mg, 1.0 mmol), NaCNBH, (383 mg, 6.0 mmol) and 3-A molecular sieves in MeCN (20 mL) at room temperature was added as solution, kept at 0°C, of MejSiCl (652 mg, 6.0 mmol) in MeCN (6 mL). The reaction mixture was stirred for 5 h at room temperature, filtered through Celite, and poured into ice-cold saturated aqueous NaHCOj. The aqueous phase was repeatedly extracted with CHjClj. The combined extracts were washed with saturated aqueous NaHC03, dried (MgSOj), filtered, and concentrated. The residue was subjected to silica gel column chromatography (toluene/ethyl acetate 2 1) to yield 15 (375 mg, 76%), [< ] +19.3° (c 1.0, CHClj). Regioisomer 16 (13%) was also obtained. 

To a solution cooled at -78°C containing 357 mg (0.596 mmol) of 2-azido-3-0-(2,3,4,6-tetra-0-acetyl-P D-galactopyranosyl)-4,6,0-isopropylidene-2-deoxy-D-galactopyranose 23 and 332 p,L (2.38 mmol) of EtjN in 10 mL of CH2C12, was added dropwise 89.3 j.L (0.894 mmol) of sulfuryl chloride over 10 min. The mixture was stirred at the same temperature for 30 min, 5 mL of saturated NaHCOj was added, and the organic layer was processed as usual. After drying in vacuo for 5 h, the crude product was purified by flash chromatography on silica gel column (EtOAc-hexane, 1 1 to 2 1) to afford 337 mg of pure a-chloride 24 in 92% yield. 

To a solution of2 (340 mg, 0.9 mmol) in THF (30 mL) cooled to —78°C K-Selectride (1.34 mL of a 1 -M solution in THF) was slowly added (1 h) under nitrogen atmosphere. The reaction mixture was stirred for an additional 1 h, quenched with an aqueous saturated solution of NaHC03 (20 mL) and allowed to attain room temperature. The product was extracted with ethyl acetate (4 x 20 mL), the combined extracts were dried (MgS04) and concentrated to dryness. The residue was dissolved in dichloromethane (30 mL), then triethylamine (500 p,L, 3.6 mmol), acetic anhydride (250 p.L, 2.6 mmol), and a crystal of AJA-dimethylaminopyridine (DMAP) were added, and the mixture was left under nitrogen at room temperature. After 24 h the solution was concentrated to dryness and the residue was chromatographed on a silica gel column with hexane-ethyl acetate (3 1) to give 25,35,4/ ,6/ -3,4-diacetoxy-2-(l-menthyloxy)-6-(2-furyl)-tetrahydropyran 4 (290 mg, 79%) mp 127°-129°C, [a]D - 5.3° (c 0.8, CHC13). 

To a suspension of sodium hydride (0.48 g, 20 mmol) in N,Al-dimethylformamide (DMF 20 mL) at — 5°C under nitrogen water (0.18 mL, 10 mmol) in 5 mL of DMF was added, followed by a larger portion of 5 and 6 (3.6 g, 9.1 mmol). After 2 h, a solution of benzyl bromide (2.38 mL, 20 mmol) in dry DMF (20 mL) was added and the mixture was left at room temperature. After 24 h, ethanol (2 mL) was added and the mixture was poured into aqueous saturated ammonium chloride solution (100 mL). The product was extracted with ethyl acetate, the extracts were dried (MgS04) and concentrated to dryness. The residue was purified by chromatography on silica gel column using toluene-ethyl acetate (9 1) for elution to yield 7 and 8 (3.37 g, 83%). 

To a solution of 2,3-O-isopropyIidene-D-glyceraldehyde (12.6 g, 97 mmol) in furan (20 mL), chloroacetic acid (5.7 g, 60 mmol) dissolved in furan (20 mL) was added and the mixture was refluxed for 8 h. After 12 h at room temperature saturated aqueous NaHCOj solution (50 mL) was added and the product was extracted with ether (3 x 100 mL). Combined ether extracts were dried (MgS04), concentrated to dryness, and the residue was chromatographed on a silica gel column with light petroleum-ether-methanol (6 4 0.5) to yield If ,2ft- and lS,2ft-l-C-(2-furyl)-2,3-0-isopropylidene-glycerols 1 (95 5, 7.0 g, 36.5%). 

Protected methyl ester 76 (0.14 g, 0.38 mmol) was dissolved in a soln of MeOH saturated with ammonia. This mixture was stirred for 3 h at rt, at which time the MeOH was removed under reduced pressure. The resulting residue was chromatographed (silica gel column, EtOAc/hexane 5 2) to give 77 as a white solid yield 0.1 g (76%) mp 162-163 °C [a]D +143.4 (c 1.0, MeOH) FABMS mlz [M+H]+ 350. 

Column chromatography is generally used for compositional analyses (ASTM D-2007 ASTM D-2549). The former method (ASTM D-2007) advocates the use of adsorption on clay and clay-silica gel followed by elution of the clay with pentane to separate saturates, elution of clay with acetone-toluene to separate polar compounds, and elution of the silica gel fraction with toluene to separate aromatic compounds. The latter method (ASTM D-2549) uses adsorption on a bauxite-silica gel column. Saturates are eluted with pentane aromatics are eluted with ether, chloroform, and ethanol. 

Keep the pH of bonded-phase silica column between 2.0 and 8.0 (better is pH 2.5-7.5). Solvents with a pH below 2.0 remove bonded phases all silica columns dissolve rapidly above pH 8.0 unless protected with a saturation column. 

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