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Di benzo [c,h] cinnol ine Oxides B y W. H. PoescheDibenzo[c,h] cinnoline 5-oxide has been synthesised. The compound is not identical with the hydrogen peroxide oxidation product of dibenzo[c,h]cinnoline and the sodium sulphide reduction product of 1 -nitro-2-o-nitrophenylnaphthalene, which must therefore be dibenzo[c,h]cinnoline 6-oxide, as previously supposed. Aside from steric interactions, electronic effects are made responsible for the exclusive formation of the 6-oxide in the latter two cases.[Note added in Proof.-The decomposition points of the N-oxides depend on the rate of heating and are therefore not suitable for identification. On very slow heating, the 5-and 6-oxide decomposed at 226 and 221", respectively].

4-and 6-Nitro-lJ2,3-benzothiadiazoles are prepared from the corresponding nitrobenzothiazoles by ring opening, followed by tetrazotisation (and decomposition) of the derived diaminodiphenyl disulphide, thus providing a convenient route to 4-and 6-derivatives of 1,2,3-benzothiadiazole. The method fails with 5-and 7-nitrobenzothiazole.By Fries and Reitz's method 1,2,3-benzothiadiazole yields 5-and 7-mononitro-derivatives, and not 4-and 7-isomers as previously believed.The four nitrobenzothiadiazoles are orientated for the first time, by relating elution behaviour to dipole moments. The structures of the aminobenzothiadiazoles follow .Diazotised 6-amino-1,2,3-benzothiadiazole yields the corresponding 6-hydroxy-compound but similar decompositions of the diazotised 4-and 7-amino-derivatives gave azo-dyes. THE only significant method for preparing 1,2 ,3-benzothiadiazoles is by diazotisation of o-aminothiophenols,l and a useful route to the latter is by ring opening of benzothiazoles. We recently described a method making all four nitrobenzothiazoles readily available and have now investigated the conversion of these into the corresponding nitrobenzothiadiazoles. Boggust and Cocker described an' improved method for the ring fission, using refluxing ethanolic hydrazine hydrate and employed it to prepare di-(o-amino-5-nitrophenyl) disulphide from 6-nitrobenzothiazole. We converted this disulphide into 6-nitro-lJ2,3-benzothiadiazole by Burawoy and Turner's procedure (used to prepare the Hodgson and Dodgson, J . SOC. Dyers and Colourists, 1948, 64, 65. 3 Ward and Poesche, J., 1961, 2825. 3 Boggust and Cocker, J., 1949, 355.