3- Chloro- 1,2,4-benzotriazine 1 -oxide

Substitution of chlorine in 3-chloro-l,2,4-benzotiiazine 1-oxide 49 by treatment with NaCN in methanol affords 3-methoxy-l,2,4-benzotriazine 1-oxide 52 (77GEP2538179). 

Benzotriazines (442) and their 1-oxides have been subjected to nucleophilic displacements. 3-Chloro-l,2,4-benzotriazine is readily converted into the hydrazino analog (95°, 2 min, 50% yield). The amine exchange of 3-amino-7-chloro- to 3-benzylamino-7-chloro-... 

Chloro- and 3-ethoxy-l,2,4-benzotriazine are oxidized by hydrogen peroxide/maleic anhydride to the corresponding 1-oxides in 56 and 55% yield.244 l,2,4-Benzotriazin-3-amines are oxidized primarily to the 2-oxides, but prolonged oxidation at 50 =C affords the 1,4-dioxides. Oxidation of the 1-oxides also affords the 1,4-dioxides.245... 

Triazoxide belongs to the chemical class of 1,2,4-benzotriazines and was discovered in 1978 by Bayer [57]. The lUPAC chemical name is 7-chloro-3-(lH-imi-dazol-l-yl)-l,2,4-benzotriazine-l-oxide (CAS-RN. 72459-58-6). Although there are other 1,2,4-benzotriazine-l-oxides with fungicidal activity known from the literature, triazoxide is the only one to have been commercialized. Figure 21.5 shows the chemical structure of triazoxide. 

The most appropriate technical synthesis of triazoxide [60], as described in Scheme 21.5, starts with phosgenation of 2-nitro-4-chloroaniline, followed by am-monolysis of the isocyanate. Cyclization of the formed arylurea occurs by treatment with aqueous sodium hydroxide to obtain the sodium salt of 3-hydroxy-7-chloro-l,2,4-benzotriazine-l-oxide. After acidification, the hydroxy group can be converted into the corresponding imidazolyl derivative after being transformed into the chloro compound with thionyl chloride. 

---