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Article

Photochemical behaviour of Schiff base liquid crystals based on isoxazole and isoxazoline ring. A kinetic approach

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Pages 1802-1812 | Received 04 Apr 2018, Accepted 10 Jun 2018, Published online: 27 Jun 2018
 

ABSTRACT

The kinetic study on the hydrolysis of Schiff bases (SBs) 1a-c and 2a-c induced by UV-vis was undertaken as a complementary study of the stability in solution and in bulk of the SBs. Solutions in chloroform were exposed to UV-vis and acquisition data occurred for 1a-c and for 2a-c in 21°C, 30 °C, 35°C and 40°C. Kinetic profile for 1a-c and 2a-c displayed the similar photochemical behaviour in that four temperature values. At 21°C, two kinetic regimes were observed where the decomposition of SBs is faster at the initial stage, with no linear plot of absorbance vs time, and after the kinetic profile obeyed a linear behaviour. A mathematical treatment of the experimental data was applied, which allowed associating the initial stage data with a second-order reaction, and the final stage of the hydrolysis with a first-order reaction. The mechanism of photochemical hydrolysis of SBs 1a and 2a was addressed. It was composed of three parts, the excitation, then the isomerisation and activation processes of tetrahedral intermediate and, the last process, a collapse of the intermediate to the yielded products of the hydrolysis aldehydes and amines which were detected by their UV-vis spectrum.

Graphical Abstract

Acknowledgments

V. L. thanks the facilities and kind help of IQ/UFRGS and CNANO/UFRGS. Special thanks to Dr. Alexsandro Dallegrave for the HRMS results.

Declaration of interest

The authors declare no conflict of interest. This paper is taken in part from the PhD thesis of Luma Fritsch, with a CAPES fellowship.

Supplementary Material

Supplemental data for this article can be accessed here.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by MCT/CNPq Edital Universal 01/2016 [Proc. no. 403075/2016-5]. L. F. thanks CAPES agency for her fellowship.

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