1,2,3-Benzothiadiazole

1,2,3-Benzothiadiazole is readily prepared by the diazotisation reaction of 2-aminothiophenol or its disulfide with sodium nitrite, as originally reported in 1887{{cite journal |doi=10.1002/cber.188702001423 |title=Zur Kenntniss der orthoamidirten aromatischen Mercaptane |last1=Jacobson |first1=J. |journal=Berichte der Deutschen Chemischen Gesellschaft |year=1887 |volume=20 |pages=1895–1903 }} and reviewed in several subsequent publications.{{cite journal |doi=10.1111/j.1478-4408.1948.tb02498.x |title=A Review of the Chemistry of the Arylthiadiazoles or Internal Diazo–Sulphides |last1=Hodgson |first1=H.H. |last2=Dodoson |first2=D.P. |journal=Journal of the Society of Dyers and Colourists |year=1964 |volume=64 |issue=2 |pages=65–71 }}{{cite book |doi=10.1016/B978-008096519-2.00092-8 |chapter=1,2,3-Thiadiazoles and their Benzo Derivatives |title=Comprehensive Heterocyclic Chemistry |year=1984 |last1=Thomas |first1=E.W. |pages=447–462 |isbn=9780080965192 }}{{cite book |title= Science of Synthesis |volume= 13: Category 2, Hetarenes and Related Ring Systems |editor1-last= Storr |editor1-first= R. C. |editor2-last= Gilchrist |editor2-first= T. L. |year= 2004 |doi= 10.1055/sos-SD-013-00386 |chapter= Product Class 9: 1,2,3-Thiadiazoles|isbn= 9783131122810 }}{{cite book |isbn=9783131812445 |title=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 |date=14 May 2014 |pages=93–104 |chapter=1,2,3-Benzothiadiazole |publisher=Georg Thieme Verlag }}

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By the Herz reaction anilines can be converted to benzothiadiazole. The method is attractive since less elaborate precursors (merely anilines) are required. Upon treatment with disulfur dichloride, the anilines give the intermediate 1,3,2-benzothiazathiolium salt, which is diazotised to complete the formation of a 1,2,3-benzothiadiazole. The parent system cannot be made this way, since the use of aniline in this reaction leads to formation of the 6-chloro derivative.

The molecule is planar. The N-N and S-N distances are respectively 128 and 171 picometers, indicative of multiple bond character.{{cite journal |doi=10.1016/0022-328X(91)86290-7 |title=Transition metal heterocyclic chemistry: XI. Manganese cyclopentadienyldicarbonyl complexes of 1,2,3-selena- and thiadiazoles including structural comparison of free and complexed 1,2,3-benzothiadiazole and 4-phenyl-1,2,3-thiadiazole |year=1991 |last1=Mayr |first1=Armin J. |last2=Carrasco-Flores |first2=Benjamin |last3=Cervantes-Lee |first3=Francisco |last4=Pannell |first4=Keith H. |last5=Párkányi |first5=László |last6=Raghuveer |first6=Krishan |journal=Journal of Organometallic Chemistry |volume=405 |issue=3 |pages=309–322 }}

Like naphthalene, this heterocycle is a 10-electron system.

1,2,3-benzothiadiazole is much less nucleophilic than naphthalene. Nitration is slow.{{cite journal |doi=10.1039/JR9630004794 |title=1,2,3-Benzothiadiazole. Part II. Electrophilic substitution in 4- and 6-amino-1,2,3-benzothiadiazoles |year=1963 |last1=Ward |first1=E. R. |last2=Heard |first2=D. D. |journal=Journal of the Chemical Society (Resumed) |pages=4794–4803 }} For that reason, many of its simple derivatives have been made from 2-aminothiophenols already having additional substituents.{{cite journal |doi=10.1039/J39700002250 |title=1,2,3-Benzothiadiazoles. Part I. A simplified synthesis of 1,2,3-benzothiadiazoles |year=1970 |last1=Kirby |first1=P. |last2=Soloway |first2=S. B. |last3=Davies |first3=J. H. |last4=Webb |first4=Shirley B. |journal=Journal of the Chemical Society C: Organic |issue=16 |page=2250 }}

1,2,3-benzothiadiazole is a very weak base and alkylation reactions give exclusively the 3-amino quaternary salt.{{cite journal |doi=10.1039/J39700002060 |title=1,2,3-Benzothiadiazole. Part VI. Investigations on the quaternisation of 1,2,3-benzothiadiazole and 1,2,3-benzoselenadiazole |year=1970 |last1=Jaffari |first1=G. A. |last2=Nunn |first2=A. J. |last3=Ralph |first3=J. T. |journal=Journal of the Chemical Society C: Organic |issue=15 |page=2060 }}

1,2,3-benzothiadiazole has been claimed to synergise insecticides including dicrotophos{{cite journal |doi=10.1021/jf60170a011 |title=Benzothiadiazoles, a novel group of insecticide synergists |year=1970 |last1=Felton |first1=John C. |last2=Jenner |first2=Donald W. |last3=Kirby |first3=Peter. |journal=Journal of Agricultural and Food Chemistry |volume=18 |issue=4 |pages=671–673 }} but has not been commercialised for that application. The only derivative to have found significant use is the fungicide acibenzolar-S-methyl.

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Category:Benzothiadiazoles