Synthesis, structural characterization and biological activity of fluorinated Schiff-bases of the type [C6H4-1-(OH)-3-(CHNArF)]

Mechanochemical Synthesis of Fluorinated Imines

A number of imines, including 12 new compounds, previously not reported in the literature, derived from variously fluorinated benzaldehydes and different anilines or chiral benzylamines were synthesized by a solvent-free mechanochemical method, which was based on the manual grinding of equimolar amounts of the substrates at the room temperature. In a very short reaction time of only 15 min, the method produced the expected products with good-to-excellent yields. The yields were comparable or significantly higher than those reported in the literature for the imines synthesized by other methods. Importantly, the conditions used for the reactions with aniline derivatives also resulted in the high yields of imines obtained from chiral benzylamines, and can be extended to the synthesis with other similar amines. Structures of all imines were confirmed by NMR spectroscopy: ¹H, ¹³C and ¹⁹F. For four compounds, X-ray structures were also obtained. The synthetic approach presented in this paper contributes to the prevention of environmental pollution and can be easily extended for larger-scale syntheses. The mechanochemical solvent-free method provides a convenient strategy particularly useful for the preparation of fluorinated imines being versatile intermediates or starting material in the synthesis of drugs and other fine chemicals.

A spectrophotometric study of impact of solvent, substituent and cross-conjugation in some 4-aminoantipyrine based Schiff bases

The influences of substituent and solvent polarity on the electronic transition of seven different 4-aminoantipyrine based Schiff bases have been investigated in 14 solvents of different polarity. Reichardt'sE_T(30) scale has been used to propose a quantitative approach towards the relative stability of the electronic ground and excited state species. The Schiff bases can sense the polarity changes of the solvents and accordingly there appear three categories of solvents: non-polar, dipolar aprotic and polar protic. The first two categories of solvents induce negative solvatochromism and the third one induces positive solvatochromism in the molecules. Cross conjugation and geometrical configuration have been proposed to play an important role in the extent of electronic transition of the Schiff bases in various solvent media. Out of various substituent effects, field effect and resonance significantly influence the electronic environment of the compounds, as evidenced from the regression models involving change in UV-Vis absorption wavelengths ¹HNMR chemical shifts and IR frequencies.