Quantitative monitoring of the progress of organic reactions using multivariate image analysis-thin layer chromatography (MIA-TLC) method

A thin layer chromatographic method combined with an image processing system (MIA-TLC) was developed for quantitative monitoring of the progress of organic reactions. Two simple reactions including alkaline hydrolysis of phenyl benzoate and reduction of benzaldehyde derivatives were chosen as model reactions. Small aliquots of starting material as well as successive aliquots of the reaction mixture in the course of the reaction were spotted on the TLC plate by micropipette. Hexane-ethyl acetate (with volume ratios of 15 : 1 and 3 : 1 for alkaline hydrolysis and reduction reactions, respectively) was chosen as the mobile phase. After TLC development, images of the plates were recorded using a home-made imaging cabinet. A home-made program was able to covert image data into three and two dimensional chromatograms, from which changes in the amount of reactants as a function of reaction time was easily monitored. By analysis of obtained chromatograms as a function of reaction time we calculated the conversion percentage of the reactions. The conversion percentage for both reactions was almost 99.9%. Also, the data enabled us to monitor the kinetics of the reactions and estimate the rate constants. Conversion of visually interpretable information to color values for quantitative analysis by MIA-TLC is a rapid and inexpensive method recommended as a powerful tool for quantitative reaction monitoring as well as a good alternative for GC in organic laboratories.