Application of TLC and HPLC/MS methods in the study of the interaction of N-phenytaconimide with 3-methyl-1-phenyl-5-aminopyrazole

Abstract

The thin layer chromatography (TLC) method is widely used for the rapid analysis of reaction masses in fine organic synthesis. The use of this method allows not only assessing the purity of substances and identify individual components, but also to monitor the progress of synthesis [1-3]. To reliably identify a large number of substances in multicomponent systems and determine the degree of conversion of starting substances, the HPLC-MS analysis method can be used [4-6]. It was previously shown that N-arylitaconimides are easily recycled by various binucleophiles when they are boiled together in various solvents, but data on the choice of reaction conditions were scattered and unsystematized. The purpose of this study was to investigate the possibility of combining several chromatographic methods to control and optimize the synthesis of pyrazolo[3,4-b]pyridine formed during the reaction N-phenylitaconimide and 3-methyl-1-phenyl-pyrazol-5-amine. The interaction of the components was carried out in low-polar as well as polar protic and aprotic solvents. For the control of the completeness of the reaction, thin layer chromatography on TLC Silica gel 60 F254 (Merck) plates was used, chloroform, methanol and their mixtures in various ratios were used as eluents. The components of the reaction mass were correlated with the declared structures using HPLC/MS studies. It was shown that the interaction of N-phenylitaconimide with 3-methyl-1-phenylpyrazol-5-amine in all studied systems for 10-15 hours did not lead to the complete conversion of the reagents. The use of aprotic solvents, both polar and low-polar, did not allow obtaining preparatively significant yields of the target product. In protic solvents, the yields of pyrazolo[3,4-b]pyridine were significantly higher. It was also shown that an increase in the protonogenicity of the medium due to the addition of acetic acid led to a more complete conversion of the reagents. The TLC and HPLC/MS data correlated well with the data on the preparative yields of pyrazolo[3,4-b]pyridine. It was found that the most suitable medium for synthesis was a mixture of propan-2-ol and acetic acid in a ratio of 25:1.