Microwave assisted sulphated titania catalyzed aldol condensation: Synthesis of some ( E ) 3-(2-naphthyl)-1-(substituted phenyl)-2-propen-1-ones under solvent-free conditions

A series of titled chalcones were synthesized by aldol condensation between 2-naphthaldehyde and various substituted acetophenones using solid acidic solid sulphated titania catalyst under microwave irradiation. The yields of these chalcones are more than 90 %. The synthesized chalcones are characterized by their physical constants, analytical and spectroscopic data

Within the above view, there is no report available for synthesis of titled compound by sulphated titania assisted aldol condensation of 2-naphthaldehyde and substituted acetophenones under microwave irradiation. Therefore the authors have taken efforts for solvent-free synthesis of titled compounds and recorded their IR and NMR spectra for characterization.

1. General
All chemicals used were purchased from Sigma-Aldrich and E-Merck chemical companies. Melting points of all chalcones were determined in open glass capillaries on SUNTEX melting point apparatus and are uncorrected. The UV spectra of all synthesized chalcones were recorded in ELICO-BL222 SPECTROMETER ( max nm) in spectral grade methanol.
Infrared spectra (KBr, 4000-400 cm -1 ) were recorded on AVATAR-300 Fourier transform spectrophotometer. Bruker AV400 NMR spectrometer has been used for recording NMR spectra, operating at 400 MHz has been utilized for recording 1 H spectra and 100 MHz for 13 C spectra in CDCl 3 solvent using TMS as internal standard. Mass spectra were recorded on a SIMADZU GC-MS2010 Spectrometer using Electron Impact (EI) techniques.
After completion of the reaction, dichloromethane (20 mL) was added, followed by simple filtration. The filtrate was concentrated and the obtained solid was purified by recrystallization. The synthesized chalcones were characterized by their physical constants, UV, IR, 1 H and 13 C NMR and Mass spectral data. Analytical and Mass spectral data are presented in Table 1.

RESULTS AND DISCUSSION
In our organic chemistry research laboratory, we attempts to synthesize aryl chalcone derivatives by crossed-aldol condensation of electron withdrawing as well as electron donating group substituted acetophenone and benzaldehydes in the presence of vigorous acidic catalyst sulphated titania in microwave irradiation.
Hence the authors have synthesized the chalcone derivatives by the reaction between 2 mmol of 2-naphthaldehyde, 2 mmol substituted acetophenones in microwave irradiation with 0.15 g of sulphated titania catalyst (Scheme 1).
During the course of this reaction sulphated titania catalyzes aldol-condensation between aryl ketone and aldehydes and elimination of water gave the chalcones. The yields of the chalcones in this reaction are more than 90 %.

CONCLUSIONS
About eleven titled chalcones were synthesized by aldol condensation between 2naphthaldehyde and various substituted acetophenones using solid acidic solid sulphated titania catalyst under microwave irradiation. The yields of these chalcones are more than 90 %. The synthesized chalcones are characterized by their physical constants, analytical and spectroscopic data. These data are supported for the formation of chalcones.