Thin-layer chromatography , organic synthesis

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 Since successful TLC can be carried out on a minute scale, only a very small fraction of the reaction mixture need be withdrawn and subjected to analysis.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. 

Classical peptide chemists were steeped in the tradition of organic chemistry in which intermediates are carefully analyzed and purified to homogeneity. Since the assembly of a desired peptide by solid-phase peptide synthesis occurs without purification of intermediates it is likely that truncated peptides and other impurities accumulate on the resin these are difficult to separate from the desired product. Prior to the 1970s, thin layer chromatography, paper chromatography, paper electrophoresis, and microchemical analysis were used to assess peptide homogeneity. None of these were sufficiently sensitive to distinguish the impurities that were expected from the solid-phase approach. 

Alkvl Azides from Alkvl Bromides and Sodium Azide General procedure for the synthesis of alkyl azides. In a typical experiment, benzyl bromide (360 mg, 2.1 mmol) in petroleum ether (3 mL) and sodium azide (180 mg, 2.76 mmol) in water (3 mL) are admixed in a round-bottomed flask. To this stirred solution, pillared clay (100 mg) is added and the reaction mixture is refluxed with constant stinring at 90-100 C until all the starting material is consumed, as observed by thin layer chromatography using pure hexane as solvent. The reaction is quenched with water and the product extracted into ether. The ether extracts are washed with water and the organic layer dried over sodium sulfate. The removal of solvent under reduced pressure affords the pure alkyl azides as confirmed by the spectra analysis."... 

Synthesis of 143 D-TA Anhydrous THF (80 mL) and Ti(0 Pr)4 were added to 140, and the mixture was stirred at ambient temperature for Ihour and cooled to —45°C. NaBH4 (6.4 g, 168 mmol) was added in one portion, and the mixture was stirred for 6 hours and warmed to 10 C, and the reaction was monitored on thin layer chromatography (TLC) for the disappearance of starting material. To the reaction mixture 142 was slowly added aqueous HCl dissolved in MeOH (60 mL, 4M), and the mixture was warmed to ambient temperature and stirred for 3 hours. After the mixture was cooled to 0°C, NaOH (5 M) was added slowly until the pH pa 12 the mixture was diluted with toluene (200 mL) and distilled under reduced pressure to remove the low-boiling-point solvents. The organic phase was allowed to separate for... 

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