Issue 9, 2017, Issue in Progress

Isocyano compounds newly recognized in photochemical reaction of thiazole: matrix-isolation FT-IR and theoretical studies

Abstract

UV-induced photoreactions of thiazole isolated in low-temperature argon matrices have been investigated by a joint use of infrared spectroscopy and density-functional-theory calculations. Photoproducts have been identified by comparison of the observed infrared spectra with the corresponding calculated spectral patterns, leading to the conclusion that undetected open-chain molecules, syn-2-isocyanoethenethiol (C[triple bond, length as m-dash]N–CH[double bond, length as m-dash]CH–SH) and 2-isocyanothiirane, are initially produced by cleavage of the CS–CN bond with hydrogen-atom migration, when the matrix samples are exposed to UV radiation coming from a super high-pressure mercury lamp for 3 min. In the secondary photolysis, syn-2-isocyanoethenethiol and 2-isocyanothiirane change to another unknown molecule, 2-isocyanoethanethial (C[triple bond, length as m-dash]N–CH2–CH[double bond, length as m-dash]S), by hydrogen-atom migration with generation of the C[double bond, length as m-dash]S double bond. These photoreaction pathways are supported by kinetic analysis of the absorbance changes of IR bands against irradiation time. We have also found that HC[triple bond, length as m-dash]N and the ˙CH[double bond, length as m-dash]CH–S˙ biradical are photodecomposed from thiazole by cleavage of the CN–CC bond following the cleavage of the CS–CN bond, where the hydrogen atom on the center carbon atom of ˙CH[double bond, length as m-dash]CH–S˙ immediately migrates to the end carbon atom to form CH2[double bond, length as m-dash]C[double bond, length as m-dash]S or to the sulfur atom to form HC[triple bond, length as m-dash]C–SH. In addition, weak bands of the species of interest in astrophysics and astrochemistry such as HC[triple bond, length as m-dash]CH, N[triple bond, length as m-dash]C–SH, HN[double bond, length as m-dash]C[double bond, length as m-dash]S, HC[triple bond, length as m-dash]NS, and the ˙CN radical are detected, but the photoconversion from thiazole to isothiazole or Dewar thiazole is not found. The ring-opening photoreaction, photoisomerization and photodecomposition pathways of thiazole isolated in low-temperature argon matrices are discussed comprehensively.

Graphical abstract: Isocyano compounds newly recognized in photochemical reaction of thiazole: matrix-isolation FT-IR and theoretical studies

Supplementary files

Article information

Article type
Paper
Submitted
29 Nov 2016
Accepted
27 Dec 2016
First published
17 Jan 2017
This article is Open Access
Creative Commons BY-NC license

RSC Adv., 2017,7, 4960-4974

Isocyano compounds newly recognized in photochemical reaction of thiazole: matrix-isolation FT-IR and theoretical studies

J. Miyazaki, H. Takiyama and M. Nakata, RSC Adv., 2017, 7, 4960 DOI: 10.1039/C6RA27496J

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