2,1,3-Benzothiadiazole Explained

2,1,3-Benzothiadiazole is a bicyclic molecule composed of a benzene ring that is fused to a 1,2,5-thiadiazole.

Preparation and structure

2,1,3-Benzothiadiazole has been known since the 19th century. It is readily prepared in at least 85% yield from o-phenylenediamine by reaction with two equivalents of thionyl chloride in pyridine. The by-products are sulfur dioxide and HCl.[1]

There are a number of alternative methods used to make this heterocycle and these have been reviewed.[2] [3] The crystal structure of the compound was determined in 1951, when it had the common name piazthiol(e).[4]

Reactions

The extent of the aromaticity of the compound was examined by a study of its proton NMR spectrum and comparison with naphthalene, which allowed the conclusion that it and related oxygen and selenium heterocycles did behave as 10-electron systems in which the 2-heteroatom contributed its lone pair to the ring current, in accordance with Hückel's rule.[5]

As a result, 2,1,3-benzothiadiazole undergoes the standard chemistry of aromatic compounds, for example readily forming nitro[1] and chloro derivatives.[6] The chemistry of this heterocycle and its simple derivatives has been reviewed.[7]

Under reducing conditions, 2,1,3-benzothiadiazoles can be converted back to the 1,2-diaminobenzene compounds from which they were prepared. This can be a useful way to protect a pair of reactive amino groups while other transformations are performed in the benzene ring to which they are attached.[8]

Bromination of 2,1,3-Benzothiadiazole is commonly performed to synthesize 4,7-dibromo-2,1,3-benzothiadiazole. This derivative is extensively used as building block in the design and synthesis of larger molecules and conductive polymers via Suzuki-Miyaura cross-coupling reactions.[9]

Derivatives

2,1,3-Benzothiadiazole derivatives containing carbazole units have been found to be luminiscent, with high emission intensity and quantum efficiency.[10]

Different π-extended molecular systems based on 2,1,3-benzothiadiazole have been built to study fundamental structure–property relationships. One example of this type of oligomer consist of extended thiophene building blocks as electron donors and 2,1,3-benzothiadiazole as electron aceptor. This oligomer was synthesized using a Sonogashira cross-coupling reaction and it showed low HOMO–LUMO gaps which could be interesting for organic semiconductor applications.[11]

Asymmetric derivatives with diphenylamine donors, cyanoacrylic acid acceptors and thiophene linkers bridged by a 2,1,3-benzothiadiazole have been designed as organic dyes with improved charge separation properties[12] when compared to classic cyanine[13] and hemicyanine[14] dyes.

Applications

2,1,3-Benzothiadiazole has been of interest as a redox-active organic component in flow batteries owing to its favourable solubility, low reduction potential and fast electrochemical kinetics.[15]

Such properties in derivatives containing this heterocycle have made it of growing interest in dyestuffs,[16] white light-emitting polymers,[8] [17] solar cells,[18] and in luminescence studies.[19]

Notes and References

  1. 10.1007/BF00468340 . Research on 2,1,3-thia- and selenadiazole . 1969 . Pesin . V. G. . Sergeev . V. A. . Chemistry of Heterocyclic Compounds . 3 . 5 . 662–666 . 98830770 .
  2. Book: 10.1055/sos-SD-013-00458 . Product Class 11: 1,2,5-Thiadiazoles and Related Compounds . Category 2, Hetarenes and Related Ring Systems . 2004 . 978-3-13-112281-0 . Storr . Gilchrist .
  3. 10.1055/s-0039-1690679 . Recent Developments in the Synthesis of 1,2,5-Thiadiazoles and 2,1,3-Benzothiadiazoles . 2019 . Rakitin . Oleg A. . Synthesis . 51 . 23 . 4338–4347 . 204128866 .
  4. Luzzati. Z.Z.. Structure cristalline de piasélénol, piazthiol et benzofurazane. Acta Crystallographica. 1951. 4. 3 . 193–200. 10.1107/S0365110X51000702. 1951AcCry...4..193L .
  5. 10.1007/BF00755265 . Studies in the field of aromatic heterocycles . 1970 . Fedin . E. I. . Todres . Z. V. . Chemistry of Heterocyclic Compounds . 4 . 3 . 308–313 . 91864834 .
  6. 10.1007/BF00944264 . Researches on 2,1,3-thia-and selenadiazole . 1969 . Pesin . V. G. . d'Yachenko . E. K. . Chemistry of Heterocyclic Compounds . 3 . 68–70 . 100997583 .
  7. Book: 978-3-13-181244-5 . Houben-Weyl Methods of Organic Chemistry Vol. E 8d, 4th Edition Supplement: Hetarenes III (Five-Membered Rings with Two and More Heteroatoms in the Ring System) - Part 4 . 14 May 2014 . Georg Thieme Verlag .
  8. Neto . Brenno A. D. . Lapis . Alexandre A. M. . da Silva Júnior . Eufrânio N. . Dupont . Jairton . January 2013 . 2,1,3-Benzothiadiazole and Derivatives: Synthesis, Properties, Reactions, and Applications in Light Technology of Small Molecules . . 2013. 2. 228–255 . 10.1002/ejoc.201201161.
  9. Huang . Jian . Niu . Yuhua . Yang . Wei . Mo . Yueqi . Yuan . Ming . Cao . Yong . 2002-07-01 . Novel Electroluminescent Polymers Derived from Carbazole and Benzothiadiazole . Macromolecules . en . 35 . 16 . 6080–6082 . 10.1021/ma0255130 . 2002MaMol..35.6080H . 0024-9297.
  10. Tao . Yun-Mei . Li . Hong-Yan . Xu . Qiu-Lei . Zhu . Yu-Cheng . Kang . Ling-Chen . Zheng . You-Xuan . Zuo . Jing-Lin . You . Xiao-Zeng . 2011 . Synthesis and characterization of efficient luminescent materials based on 2,1,3-benzothiadiazole with carbazole moieties . Synthetic Metals . en . 161 . 9–10 . 718–723 . 10.1016/j.synthmet.2011.01.020.
  11. Kitamura . Chitoshi . Saito . Kakuya . Ouchi . Mikio . Yoneda . Akio . Yamashita . Yoshiro . October 2002 . Synthesis and Crystal Structure of 4,7-bis (2-thienylethynyl)-2,1,3-benzothiadiazole . Journal of Chemical Research . en . 2002 . 10 . 511–513 . 10.3184/030823402103170565 . 1747-5198. free .
  12. Velusamy . Marappan . Justin Thomas . K. R. . Lin . Jiann T. . Hsu . Ying-Chan . Ho . Kuo-Chuan . 2005-05-01 . Organic Dyes Incorporating Low-Band-Gap Chromophores for Dye-Sensitized Solar Cells . Organic Letters . en . 7 . 10 . 1899–1902 . 10.1021/ol050417f . 15876014 . 1523-7060.
  13. Ehret . A. . Stuhl . L. . Spitler . M. T. . 2001-10-01 . Spectral Sensitization of TiO 2 Nanocrystalline Electrodes with Aggregated Cyanine Dyes . The Journal of Physical Chemistry B . en . 105 . 41 . 9960–9965 . 10.1021/jp011952+ . 1520-6106.
  14. Yao . Qiao-Hong . Meng . Fan-Shun . Li . Fu-You . Tian . He . Huang . Chun-Hui . 2003-04-16 . Photoelectric conversion properties of four novel carboxylated hemicyanine dyes on TiO2 electrode . Journal of Materials Chemistry . 13 . 5 . 1048–1053 . 10.1039/b300083b.
  15. 10.1021/acsenergylett.7b00261 . "Wine-Dark Sea" in an Organic Flow Battery: Storing Negative Charge in 2,1,3-Benzothiadiazole Radicals Leads to Improved Cyclability . 2017 . Duan . Wentao . Huang . Jinhua . Kowalski . Jeffrey A. . Shkrob . Ilya A. . Vijayakumar . M. . Walter . Eric . Pan . Baofei . Yang . Zheng . Milshtein . Jarrod D. . Li . Bin . Liao . Chen . Zhang . Zhengcheng . Wang . Wei . Liu . Jun . Moore . Jeffery S. . Brushett . Fikile R. . Zhang . Lu . Wei . Xiaoliang . ACS Energy Letters . 2 . 5 . 1156–1161 .
  16. Frizon . Tiago Elias Allievi . Valdivia Martínez . Julio César . Westrup . José Luiz . Duarte . Rodrigo da Costa . Zapp . Eduardo . Domiciano . Kelvin Guessi . Rodembusch . Fabiano Severo . Dal-Bó . Alexandre Gonçalves . December 2016 . 2,1,3-Benzothiadiazole-based fluorophores. Synthesis, electrochemical, thermal and photophysical characterization . Dyes and Pigments. 135. 26–35 . 10.1016/j.dyepig.2016.07.011.
  17. Book: 10.1007/978-3-642-14935-1_2 . White-Emitting Polymers and Devices . WOLEDs and Organic Photovoltaics . Green Energy and Technology . 2010 . Wu . Hongbin . Ying . Lei . Yang . Wei . Cao . Yong . 37–78 . 978-3-642-14934-4 . 54914788 .
  18. 10.1039/C6TC01860B . free . Benzothiadiazole and its π-extended, heteroannulated derivatives: Useful acceptor building blocks for high-performance donor–acceptor polymers in organic electronics . 2016 . Wang . Yang . Michinobu . Tsuyoshi . Journal of Materials Chemistry C . 4 . 26 . 6200–6214 .
  19. Sukhikh . Taisiya . Ogienko . D. . Bashirov . D. . Konchenkoa . S. . May 21, 2019 . Luminescent complexes of 2,1,3-benzothiadiazole derivatives . Russian Chemical Bulletin . 68. 4 . 651–661 . 10.1007/s11172-019-2472-9. 182415426 .

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