Copper herbicidal action

It was already recognised by the turn of the century that high doses of fertilisers, such as Chile salpetre (NaNOj), ammonium sulfate, calciiun cyanamide and kainite (KCl, MgSO SHjO) exhibit herbicidal action. Remy and Vasters (1914) were the first to observe the phenomenon of synergism in combined preparations. They established that 10% of kainite mixed with calcium cyanamide was more active than double doses of the single components used alone. A similar enhancement of action was observed by Bolley (1901) in the case of mixtures of copper sulfate and sodium arsenite. 

A number of useful replacement reactions in the 2,1,3-benzothiadiazole series involve the production and reactions of their nitriles. 4,7-Dicyano-2,l,3-benzothiadiazole is of particular interest because of its potent herbicidal and defoliating activity. It is produced by the action of a pyridine-copper(n) cyanide complex on the readily available 4,7-dibromo-compound. Other nitriles of this series are similarly obtained. A second method, of more limited applicability, is the Sandmeyer reaction, which, in the present instance, gives improved results when the amino-2,1,3-benzothiadiazoles are diazotized with nitrosyl-sulphuric acid. The nitriles are convertible by conventional methods into other functional derivatives. Successive coupling with diazotized aniline, and... 

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