Synthesis and study of mesomorphic properties of unsymmetrical cyclohexanone-derived bis-chalcones

ABSTRACT

A series of (2E,6E)-2-(4-n-alkoxybenzylidene)-6-((benzo[d][1,3]dioxol-6-yl)methylene)cyclohexanones were synthesised by stepwise condensation reactions from cyclohexanone. The optical and thermal analysis of the series indicated the mesomorphic properties of some derivatives. The compounds with C7–C16 substituents showed the nematic phases in the range of 90–73°C. The single crystal X-ray analysis confirms the head to tail packing arrangement.

GRAPHICAL ABSTRACT

KEYWORDS:

• Liquid crystals
• mesomorphic
• aldol condensation
• chalcogens

Acknowledgements

We are grateful to DST-PURSE for the single crystal X-ray diffraction and UGC for the polarising optical microscope facility of the Faculty of Science. We also thank Prof. Sandeep Kumar of Raman Research Institute, Bangalore, for the DSC analysis.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental data

Supplemental data for this article can be accessed here

Notes

1. (E)-2-((Benzo[d][1,3]dioxol-6-yl)methylene)cyclohexanone (6): A round-bottom flask was charged with piperonal (1.0 g, 6.66 mmol), cyclohexanone (0.98 g, 9.99 mmol), NaOH (0.53 g, 13.32 mmol) and water (70 mL). This mixture was stirred at room temperature (15 h). The reaction was quenched with water and dil. HCl and extracted with ethyl acetate (3 × 25 mL). The combined organic phase was washed with water and dried over anhydrous sodium sulphate. Solvent was removed in vacuum and the crude product was purified by column chromatography on silica gel to afford the product 6 as white solid (0.92 g, 60.0%); m.p. 87°C (Reported 87–88°C [16]).(2E,6E)-2-(4-Octyloxybenzylidene)-6-((benzo[d][1,3]dioxol-6-yl)methylene)cyclohexanone (3d): A round-bottom flask was charged with 6 (0.25 g, 1.086 mmol), 4-octyloxy benzaldehyde (0.25 g, 1.086 mmol), NaOH (0.065 g, 1.63 mmol) and MeOH (15 mL). This mixture was heated (60–70°C; 4 h). The reaction mixture was quenched with water and dil. HCl and extracted with ethyl acetate (3 × 25 mL). The combined organic phase was washed with water and dried over anhydrous sodium sulphate. Solvent was removed in vacuum and the crude product was purified by column chromatography on silica gel to afford 3d as yellow crystalline solid (0.407 g, 84.43%). ¹H-NMR (400 MHz, CDCl₃): δ 7.77 (s, 1H), 7.72 (s, 1H), 7.46 (d, J = 8.8 Hz, 2H), 7.02–7.01 (d, J = 7.6 Hz, 1H and one singlet of aromatic H merged with doublet), 6.94 (d, J = 6.8 Hz, 2H), 6.87 (d, J = 7.6 Hz, 1H), 6.02 (s, 2H), 4.01 (t, J = 6.8 Hz, 2H), 2.95–2.91 (m, 4H), 1.85–1.77 (m, 4H), 1.50–1.44 (m, 2H), 1.36–1.30 (m, 8H), 0.91 (t, J = 7.2 Hz, 3H)IR (KBr): υ 3061, 2924, 2850, 1656, 1591, 1556, 1508, 1491, 1259, 1160, 924, 560, 508 cm⁻¹Mass (EI): m/z (%) (M + 1) 447 (57), 446 (78), 445 (100), 444 (66), 431 (34), 333 (31), 332 (44). Other details about the experimental data and spectroscopic data are available in the Supplemental data.

2. Details of crystallographic analysis of 3d have been deposited with the Cambridge Crystallographic Data Centre (CCDC 1036816). Copies of the data can be obtained from http://www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CD21EZ, UK (fax: [phone]; e-mail: [email protected]).

Additional information

Funding

We thank Council of Scientific and Industrial Research (CSIR), New Delhi, for the award of Senior Research Fellowship to KNP.