TLC analysis

TLC analysis of the crude reaction product reveals no additional products. Similarly quantitative results are obtained using benzene, /-butanol and ether as the solvents in the irradiation of (39). The reaction is less sensitive to oxygen than most ketone photolyses resulting in products from a-cleavage processes. 

Nonyl aldehyde (32.66 g, 0.23 mol) and furan (200 mL, 187.2 g, 2.75 mol) were mixed in a 250-mL photolysis flask equipped with a quartz immersion well containing a Vycor filter and a 450-W Hanovia Lamp. The system was kept at -20° C with an isopropyl alcohol bath cooled by a Cryocool Immersion Cooler (CClOO). Nitrogen was bubbled throughout the duration of the reaction, and the solution was stirred vigorously. Additional furan (150 mL, 140.4 g, 2.06 mol) was added during the course of the reaction. TLC analysis indicated completion of the reaction after 20 h. After evaporation of excess furan and NMR analysis of the resultant oil (48.70 g, ca. 100%) indicated the desired photoadduct had been formed, without contamination from unreacted nonyl aldehyde. 

To a solution of dihydronaphthalene 41 (250 mg, 0.77 mmol) in CH2CI2 (5 mL) was added methyl trifluoromethanesulfonate (227 mg, 1.38 mmol). The mixture was stirred at rt until the starting material had been completely consumed as judged by TLC analysis (3 h). The mixture was cooled to 0°C and a solution of NaBHt (111 mg, 2.92 mmol) in 4 1 MeOH THF (3 mL) was slowly added. The mixture was warmed to rt then quenched with saturated aqueous ammonium chloride (50 mL). The resulting mixture was extracted with CH2CI2 (3 X 50 mL) and the combined organic extracts were dried over anhydrous sodium sulfate, filtered, and concentrated in vacuo. The resulting material was dissolved in 4 1 THF/H2O (5 mL) and oxalic acid (485 mg, 3.85 mmol) was added. The reaction... 

After anilide 30 (1.12 g, 4.46 mmol) is hydrolized in 6 M HCl at 100 °C (by TLC analysis), toluene (5 mL) is added and then aldehyde 5 (0.74 mL, 8.92 mmol) is added dropwise at the same temperature. The reaction was stirred for 2 h and then cooled to room, temperature. The aqueous layer is removed and neutralized with aqueous NaOH to afford 31 as a crystalline solid. The crude product is purified by silica gel chromatography (hexanesiethyl acetate, 5 1) to give 31 (802 mg, 70%) as colorless crystals, mp 103 °C. 

Thin-Layer Chromatography TLC) The function of TLC in organic synthesis is primarily one of allowing the experimenter to follow the progress of the reaction without actually interrupting the reaction. Since successful TLC can be carried out on a minute scale, only a very small fraction of the reaction mixture need be withdrawn and subjected to analysis. The following example of the TLC analysis of the chromic acid oxidation of borneol, described by Davis (3), is a useful model. 

TLC analysis of the crude product (elution with 50 1 pentane ether, visualization with iodine) showed three non-baseline spots Rf 0.65 (cis isomer), Rf 0.52 (unknown impurity), and Rf 0.32 (trans isomer). The unknown impurity is intensely sensitive to iodine and largely coelutes with the cw-isomer in the subsequent column chromatography. However, the ll NMR spectrum of this isomer shows excellent purity despite the presence of this spot on TLC. In 100 1 pentane ether, Rf values of the cis and trans isomers are about 0.50 and 0.15, respectively. 

TLC analysis (elution with 1 1 hexanes ethyl acetate) indicated that the reaction was not complete after 5 hr heating was continued overnight. 

TLC analysis indicated that the reaction was complete. TLC was performed on pre-coated plates with silica gel 60 F254 purchased from EM Sciences (Merck) using hexanes/ethyl acetate (1/1) as the eluent. 

TLC Analysis. Samples were examined by TLC using standard procedures. Rf values were determined and compared with those of authentic reference materials. Radioactive components were located by scanning (Vanguard Instrument Corp., North Haven, Conn., Model 885) or by autoradiography (Eastman Kodak, Rochester, N. Y., type AA film). The relative Rf value of DCDD on silica gel plates (Brinkmann Instruments, Inc., Westbury, N. Y., type For,4) when developed with n-hexane dioxane acetic acid, 90 10 4, V/V/V, was 0.90. The observed impurity had a relative Rf value of 0.40. On Brinkmann alumina plates, developed with n-hexane, DCDD had a relative Rf of 0.32. Neither system separated the chlorinated dibenzodioxin isomers. 

To test the quality of some synthetic dyes according to standardized procedures, a screening is recommended based on TLC analysis on silica plates 60 F 254 using elutions with an ethyl acetate pyridine water 25 25 20 (v v v) mixture. To determine purity and secondary dyes (components or by-products of a dye that are not allowed to be present), successive TLC separations are recommended or, for more accurate answers, HPLC-DAD using RP-18 columns and eluents like acetonitrile and phosphate buffer."... 

TLC analysis of oligomers was performed on Silica gel 60 aluminium sheet (Merk) using buthanol and formic acid (1 1.5) as solvent [26]. The dye reagent was prepared by dissolving 9.5 mg of 1,3 dihydroxynaphtalin (Aldrich) in 5 mL of ethanol/H2S04 mixture (1 0.05, V/V). The migration front (Rf) of each spot was measured and expressed as Rm, were ... 

Fractions rejected by 1.0 KDa (C>i) and permeated through 0.5 KDa (C0 5) membranes were also subjected to TLC analysis. In Figure 3 are reported the values relevant to the various spots detected in the two samples as a function of an arbitrary polymerisation degree (DP). The good linear correlation between these parameters allows to hypothesise a difference of one monomer units between the subsequent spots [32]. Consequently, C0.5 would correspond to the monomer, Cj to an homologous series fi om the monomer to the hexamer. 

Although TLC analysis of vitamin Bj has been reported in food and mammalian tissues, [3,4] we eould not find any arfieles for preparation of vitamin Bj and related compounds using TLC. 

Akhtar et al. [20] have studied the identification of photoproducts of fohc acid and their degradation pathways in aqueous solution using preparative TLC. An aqueous solution of folic acid irradiated with UV at pH 2.4 to 10.0 for 6 h was subjected to TLC analysis, which gave separation of fohc add (Rj 0.67), p-woi-nobenzolyl-L-glutamic acid (Figure 10.12). The photolyzed solutions were... 

Pukl, M. and Prosek, M. (1990). Rapid quantitative TLC analysis of sugars using an improved commonly used solvent system. /. Planar Chromatogr. 3,173-176. 

Plastic foils used for wrapping TLC plates were once reported to contain amides of oleic, stearic, or palmitic acid as antiblocking agents which may migrate from the wrapping material [28]. Similarly, Amos [447] has encountered interferences from contaminants in solvents in the TLC analysis of phenolic AOs in turbine oils. 

In the area of process monitoring TLC has been used for the study of the thermal decomposition of zinc di-isopropyl dithiophosphate (antiwear additive in lubricating oils) [458]. TLC analysis has been reported as a quality control tool for analysis of dispersing agents (alkylsalicylates, thioalkylphenolates), AOs (dithiophosphates, dialkyldithiophosphates) and their intermediates in lubricating oil (UV detection,... 

Thin-layer chromatography is employed in many areas of QC and routine monitoring of product quality [458]. Fluorescence scanning, densitometry or videodensitometry are used for quantification. Not all polymer additives are amenable to TLC analysis. Some fatty acid amides are virtually insoluble in organic solvents and cannot be isolated by thin-layer or column chromatography. 

The number of reports on on-line TLC analysis of extracts is quite limited. Stahl [16,29] described a device for supercritical extraction with deposition of the fluid extract on to a moving TLC plate. On-line SFE-TLC provides rapid and simple insight into the extraction performance. Its strength is that the extract is deposited on a plate, which means that detection is a static process. Limitations of SFE-TLC are that quantification is difficult, and that the stability of components on the support material or in the presence of oxygen may be a problem. For additives in beverages (such as benzoic... 

A series of 200-mL tractions was collected during flash chromatography. The product was eluted in fractions 3-8 as indicated by TLC analysis using 4% ethanolic phosphomolybdic acid stain. 

Figure 12.8 A. 2-PS reaction. B. Surface representations of the CHS (left) and 2-PS (right) active site cavities are shown. The catalytic cysteines (red), the three positions that convert CHS into 2-PS (green), and the substitution that does not affect product formation (blue) are highlighted. C. TLC analysis of CHS, 2-PS, and CHS mutant enzymes. The radiogram shows the radiolabeled products produced by incubation of each protein with [14C]malonyl-CoA and either p-coumaroyl-CoA (C) or acetyl-CoA (A). Numbering of mutants corresponds to CHS with 2-PS numbering in parenthesis. Positions of reaction products and their identities are indicated.

Reactions were carried out in a glass vessel closed with a septum cap. Neither molecular sieve nor drying gas was used. The glycosyl donor (0.41 mmol, 1 equiv) in CH2C12 (3 ml) was treated with Ph3P (3 equiv) and CBr4 (3 mol equiv) and stirred for 3h at room temperature. Then, the N,N-tetra-methylurea (300 pi) and the glycosyl acceptor (3 equiv) were added and stirred at room temperature. The reaction was monitored by TLC analysis until the bromide donor was... 

The reaction mixture was stirred for 2h at room temperature until TLC analysis indicated that the reaction was complete. The solution was filtered through Celite and washed with dichloromethane. The filtrate was washed with saturated aqueous NaHC03 and H20. The organic phase was dried (MgS04), filtered and the filtrate was concentrated to dryness. Purification of the crude product by column chromatography over silica gel afforded the target compound. 

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