Microwave assisted solvent-free synthesis and biological activities of novel imines (Schiff bases)

Abstract

Twelve new ortho-Hydroxyketimines were synthesized by conventional as well as microwave method and evaluated for their antinemic activity against Meloidogyne incognita [(Kofoid and White) Chitwood]. Conventional methods for synthesis of Schiff bases require refluxing at 140°C of the reactants in different solvents for at least 24 h or more, where as the microwave-assisted synthesis has brought down the reaction time from 24 h to 1 minute. The procedure reported is simple as it does not require any organic solvents and the time has been reduced to only 1 minute. Comparative yields of all compounds by different methods revealed that the yield was low in conventional method (79–87%) as compared to microwave assisted synthesis (94–97%). The bioassay revealed that all the test compounds exhibited promising nematicidal activity; N-propyl-2-hydroxypropiophenonimine being the most effective with LC₅₀ value of 74.46 mgL⁻¹ followed by N-hexyl-2-hydroxyacetophenonimine with LC₅₀ value of 99.60 mgL⁻¹ after 72 h of exposure. The results obtained from bioassay indicated that this class of compounds has not only given a lead with regard to potential of Schiff bases in pest control, but has suggested that a carbon chain length of 6 atoms in the side chain is optimum on the basis of structure activity relationship (SAR).

Keywords:

• Schiff's bases
• antinemic
• environmentally benign
• microwave
• Meloidogyne incognita [(Kofoid and White) Chitwood]

Acknowledgments

The first author is grateful to the Indian Council of Agricultural Research for a junior research fellowship.

This paper was presented at the IUPAC sponsored International Conference on Agrochemicals Protecting Crop, Health and Natural Environment held in New Delhi, India, January 8–11, 2008.