Column chromatography separated compounds

As would be anticipated by the method of synthesis, two isomeric products were formed in a ratio of about 3 1 and these were easily separated by column chromatography. The compound formed in greater amount proved to be identical to th material isolated from the first preparation. A study of the C nmr spectra indicated that the more active isomer was the nicotinate 10 and this was based primarily on the coupling of the carboxyl carbon atom with the C-4 proton. 

Additional peaks and improved resolution of peaks were obtained after cleanup and column chromatography separations. The method of analysis is described by the flow diagram shown in Figure 3. An aliquot of the air-dried dust was slurried with water, adjusted to pH 3 with sulfuric acid, and then repeatedly extracted in a Waring blendor with a solvent mixture of hexane and diethyl ether, 1 + 1 (v./v.). A portion of the extract was used for herbicide analysis in which methylation with diazomethane and gas chromatography were employed for the detection of the methyl ester of the chloro-alkyl phenoxy compounds. 

US EPA published its initial list of 187 organic compounds found in US drinking water in 1975. Analyses were performed using GC-MS (gas chromatography with mass spectroscopy) and a packed column to separate organic compounds. Present-day analyses using a capillary column to separate compounds have increased the resolution of GC-MS detection several fold (7). 

The setup shown in Figure 2.19 is the simplest example of liquid chromatography. The column diameter for such chromatographs usually varies from 1 to 5 cm. The column is filled with fine adsorbent particles. The top of the column is open for the entire duration of the experiment. The sample dissolved in a small amount of the solvent is introduced first in the column. After this, the solvent is introduced slowly but continuously into the column and separated compounds or fractions of compounds exit the column at the bottom. In this method, the solvent flows only under the influence of gravitational force. The disadvantage of this... 

Ion-exchange chromatography separates compounds on the basis of their molecular charges. Compounds capable of ionization, particularly zwitterionic compounds, separate well on ion-exchange column. The separation proceeds because ions of opposite charge are retained to different extents. The resolution is influenced by ... 

Series of selenium-containing phosphorus compounds (137-139) have been reported by Kimura and Murai. Phosphinoselenoic amides 137 were prepared from racemic phosphinoselenoic chlorides (138) and chiral amines and the individual isomers could be separated by column chromatography in some cases.Reaction of 137 with tributylphosphine afforded the P(III) aminophosphines with retention of configuration at the phosphorus atom. (5)-methylbenzylamine was also used to prepare both enantiomers of phosphinoselenoic chlorides 138 in 96% ee. In contrast to the oxygen analogues, they were found to be stable and could be purified by column chromatography. Several compounds, such as 139 for example, were prepared by stereoselective nucleophilic substitutions of the Cl atom. ... 

Although we have emphasized that the fundamental principle of electrophoretic separation is different from that of chromatography, there are many similarities in the appearance of the separation. There is sample injection, flow of a carrier fluid along a column, similar detectors employed near the end of the column, and separated compounds being displayed as peaks emerging at characteristic times. Similar formulas can be used to describe the resolution of separations and to... 

The main difference between the first four methods [normal chamber RPC (N-RPC), microchamber RPC (M-RPC), ultra-microchamber RPC (U-RPC), and column RPC (C-RPC) 1 lies in the size of the vapor space, that is an essential criterion in rotation planar chromatography. The circular mode of development is always used for on-line preparative separations by all of these methods. The sample is applied near the center of the layer, and the mobile phase is forced through the stationary phase from the center to the outside of the round plate/planar column. The separated compounds are eluted from the layer/planar column as a result of the centrifugal force and collected in a fraction collector. 

Under the protection of nitrogen, compound 3.63 (88 mg, 0.19 mmol) was dissolved in benzene (10 mL) and heated to 80 °C, TEMPO (304 mg, 1.95 mmol), and tributyltin hydrogen peroxide (0.434 mL, 1.56 mmol) were introduced slowly within 30 min to the solution. The reaction was kept refluxing for 2 h. TLC showed that the reaction was completed. After cooled to room temperature, the mixture was filtered by sihca gel, the solvent was removed by rotary evaporator, and the resulting crude product was purified by flash column chromatography separation (PE/EA = 20 1), to give 77 mg white solid Rf = 0.65, PE/EA = 5 1), yield 75 %. 

It has already been described that a number of unsymmetrical tetrachalcogenafulvalenes can be prepared by a cross-coupling reaction of the corresponding l,3-dithiole-2-ones or 1,3-diselenoIe-2-ones, via triethyl phosphite, followed by column chromatography separation of the cross-coupled product (CCP) from the self-coupled byproducts (SCPs), if there is a considerable difference in the Rp values of the CCP and SCPs. For example, the Rf values of compounds (la -la ), (7b-7b), (8c-8c), (lOc-lOc), (12c-12c), (13a -13a ) and (29-29) are 0.75, 0.77, 0.55, 0.49, 0.25, 0.08, 0.05, respectively, on a silica gel plate using CH2CI2 as eluent, i.e., the polarity of the latter compounds is larger... 

The nitration of the 2-anilino-4-phenylselenazole (103) is much more complicated. Even careful nitration using the nitrate-sulfuric acid method leads to the formation of a mixture of variously nitrated compounds in an almost violent reaction. By the use of column chromatography as well as thin-layer chromatography a separation could be made, and the compounds could be partly identified by an independent synthesis. Scheme 33 shows a general view of the substances prepared. Ring fission was not obser ed under mild conditions. 

Acetaldehyde can be isolated and identified by the characteristic melting points of the crystalline compounds formed with hydrazines, semicarbazides, etc these derivatives of aldehydes can be separated by paper and column chromatography (104,113). Acetaldehyde has been separated quantitatively from other carbonyl compounds on an ion-exchange resin in the bisulfite form the aldehyde is then eluted from the column with a solution of sodium chloride (114). In larger quantities, acetaldehyde may be isolated by passing the vapor into ether, then saturating with dry ammonia acetaldehyde—ammonia crystallizes from the solution. Reactions with bisulfite, hydrazines, oximes, semicarb azides, and 5,5-dimethyl-1,3-cyclohexanedione [126-81 -8] (dimedone) have also been used to isolate acetaldehyde from various solutions. 

A mixture of 4,5-di(pentyloxy)phthalonitrile (A 69 mg, 0.23 mmol), 3,4,5,6-tetraphenylphthalonitrile (B lOOmg, 0.23 mmol), Ni(0Ac)2 (35 mg, 0.2mmol). and catalytic amounts of DBU in pentan-l-ol (3mL) was heated under N2 for 24 h under reflux. The cooled blue-green solution was poured into MeOH/H20 (5 1, 50 mL), and the precipitate formed was centrifuged, washed with MeOH, and dried in vacuo. The separation of the prepared compounds was performed by column chromatography (toluene/hexane 1 1). The fractions were collected and the solvent evaporated. The order of elution was ABBB (0.5 mg, 0.1 %), ABAB (7.5 mg, 1.4%), AABB (2 mg, 0.5%), AAAB (15 mg, 2.3%) and AAAA (9 mg, 1.6%). No BBBB-type phthalocyanine was formed. 

Next we studied high temperature bromination of benzobarrelene at 150 C. NMR analysis indicated that the reaction mixture was very complex and consisted of at least ten products. After repeated column chromatography combined with fractional crystallization we have been able to separate 18 compounds (Scheme 6). Four of them were bromoalcohol compounds 18, 12, 22 and 2fl. After high temperature bromination we expected three isomeric non-rearranged products with benzobarrelene skeleton and isolated 22, 22, and 24 in yields of 34, 9.3, and 6.2 %, respectively. Because of the very close structural similarity we were not able to make a clear-cut differentiation between the stereochemistry of 22 and 24-Therefore, we carried out an X-ray analysis (ref. 9) of the isomer 22-... 

Because of the instability of many of the compounds involved, it is necessary to determine the chemical recoveries in all cases. This requires the use of macro quantities (10 mg up to several hundred mg) of carriers and target compounds. This, in turn, makes it impractical to use the various thin-layer methods, such as paper and thin-layer chromatography and paper electrophoresis, although such methods have proved useful in identifying products and in checking the purity of fractions. The separation methods now most commonly used are column chromatography and sublimation. 

It is fruitless to attempt detailed study of a phenomenon whose products are not well identified. It is unfortunately frequently noted in the literature, especially in cases of column chromatography, that fractions are only identified as to the chemical operations which brought them to light. Fractions are identified, for example, only by the solvent used. Speculations as to the composition of the radioactive solutes in such solutions can seldom be really reliable, and the presence of an unexpected radioactive species is in such cases undetectable. It is also important in reading the literature to watch out for cases in which the chemical yields of the carriers have not been measured. Extensive decomposition can often occur on silica gel and alumina columns, especially when photosensitive or moisture sensitive compounds are used. For these reasons much of the information now existing in the literature must be regarded as only exploratory, awaiting the development of better analytical methods for separation, purification, identification and determination of the products —known or expected. 

This method requires about 40 g of tobacco which are extracted with ethyl acetate in the presence of ascorbic acid. A trace amount of C-NDELA is added as an internal standard for quantitative analytical work. The filtered extract is concentrated and NDELA is enriched by column chromatography of the concentrate on silica gel. The residues of fractions with p-activity are pooled and redissolved in acetonitrile. Initially, we attempted to separate NDELA on a 3% OV-225 Chromosorb W HP column at 210 C using a GC-TEA system with direct interface similar to the technique developed by Edwards a. for the analysis of NDELA in urine (18). We found this method satisfactory for reference compounds however, it was not useful for an optimal separation of NDELA from the crude concentrate of the tobacco extract (Figure 4). Therefore, we silylated the crude concentrate with BSTFA and an aliquot was analyzed by GC-TEA with direct interface. The chromatographic conditions were 6 ft glass column filled with 3% OV-... 

Applications Open-column chromatography was used for polymer/additive analysis mainly in the 1950-1970 period (cf. Vimalasiri et al. [160]). Examples are the application of CC to styrene-butadiene copoly-mer/(additives, low-MW compounds) [530] and rubbers accelerators, antioxidants) [531]. Column chromatography of nine plasticisers in PVC with various elution solvents has been reported [44], as well as the separation of CHCI3 solvent extracts of PE/(BHT, Santonox R) on an alumina column [532]. Similarly, Santonox R and Ionol CP were easily separated using benzene and Topanol CA and dilaurylthiodipropionate using cyclohexane ethyl acetate (9 1 v/v) [533]. CC on neutral alumina has been used for the separation of antioxidants, accelerators and plasticisers in rubber extracts [534]. Column chromatography of polymer additives has been reviewed [160,375,376]. 

Liquid Chromatography. - Diasteriomeric phosphonodipeptides have been separated by ion exchange column chromatography.267 H.p.l.c. has been used for the analysis of a variety of biologically active phosphorus compounds, such as aminoacid phosphate esters,26 phosphinothrycin,269 inositol triphosphate,270 fructose diphosphate,271 pyridoxal phosphate,272 and ATP.273... 

Other methylphenyl(2-phenylpropyl)stannyl-transition metal complexes are oily compounds 18). Fractional recrystallization could therefore not be applied to separate those diastereomers. For the irondicarbonylcyelopentadienyl compound (77), the diastereomeric ratio (77)A/(77)B = 45/55 could be reached by the standard route (see Fig. 9) but could not be modified by column chromatography. 

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